Although IBM no longer seems in a
position to dictate the majority of PC standards (Intel and
Microsoft seem to have taken on that role), all of the
original PC specifications and standards were determined by
IBM and set forth in its original line of personal computers.
From these original IBM PC, XT, and AT systems came many of
the standards to which even today's systems must still
conform. This includes motherboard form factors, case and
power supply designs, ISA Bus architecture, system resource
usage, memory mapping and architecture, system interfaces,
connectors, pinouts, and more. As such, nearly every
PC-compatible system on the market today is based in some form
on one or more of the original IBM products. The original line
of systems are often called Industry Standard Architecture
(ISA) systems, or Classic PCs. IBM calls
them Family/1 systems.
This chapter serves as a technical
reference to IBM's original family of personal computer
systems. Much of the information in this chapter serves as a
sort of history lesson; it is easy to see how far
IBM-compatible computing has come when you look over the
specifications of the original systems the PC standard is
based on! I find the information valuable to teach others the
origins of what we call a PC-compatible system
today.
Because the PC compatibles are mostly
based on the IBM XT and especially AT systems, you can see
where things like the motherboard, case, and power supply
shapes came from, the positions of slots, connectors and other
components on the boards, and the levels of performance these
systems originally offered.
Although these systems have long since
been discontinued, I am amazed that I still find many of these
systems in use. From individuals to large corporations to the
government and military, I still occasionally encounter these
old systems in my training and consulting practice. Often the
only part that remains of the original system is the case and
power supply, because newer Baby-AT form factor motherboards
easily fit in most of the original IBM machines. In fact, I
still have several of the original IBM XT and AT cases around
which now sport modern Pentium motherboards, large hard
drives, and all new components!
System-Unit
Features by Model
The following sections discuss the
makeup of all the various versions or models of the original
IBM systems, and also technical details and specifications of
each system. Every system unit has a few standard parts. The
primary component is the motherboard, which has the CPU
(central processing unit, or microprocessor) and other primary
computer circuitry. Each unit also includes a case with an
internal power supply, a keyboard, certain standard adapters
or plug-in cards, and usually some form of disk
drive.
There is an explanation of each
system's various submodels and details about the differences
between and features of each model. Also shown are the changes
from model to model and version to version of each
system.
Included for your reference is
part-number information for some of the systems and options.
This information is for comparison and reference purposes
only; all these systems have been discontinued and generally
are no longer available. However, it is interesting to note
that IBM still stocks and sells component parts and assemblies
for even these discontinued units. IBM still stocks
replacement parts even for the original PC, XT, and AT
systems!
The original IBM systems can be
identified not only by their name, but by a number assigned to
each system. IBM normally put the name of the computer on a
small 1x1-inch square brushed metal plate on the front cover,
and the system number on a similar metal plate on the rear of
the chassis. The system names and numbers correspond as
follows:
System Number |
System Name |
4860 |
PCjr |
5140 |
PC Convertible (laptop) |
5150 |
PC |
5155 |
Portable PC (really a portable XT) |
5160 |
XT |
5162 |
XT-286 (really an AT) |
5170 |
AT |
Note that because modern PC components
are often designed to be physically compatible with the
original IBM systems, you can (and usually should) replace any
failed or obsolete components in the older IBM systems with
non-IBM replacement parts. Invariably, you will be able to
obtain upgraded or improved components compared to the
originals, and at a greatly reduced price. An example is one
original 286 IBM AT that I have that now sports a Pentium MMX
motherboard, 64M of RAM, 9G SCSI drive, 12x CD-ROM, and a host
of other options. Of course, the only original IBM parts left
in the system are the case and power supply, which are both
more than 14 years old!
An Introduction
to the PC (5150)
IBM introduced the IBM Personal
Computer on August 12, 1981, and officially withdrew the
machine from marketing on April 2, 1987. During the nearly
six-year life of the PC, IBM made only a few basic changes to
the system. The basic motherboard circuit design was changed
in April 1983 to accommodate 64K RAM chips. Three different
ROM BIOS versions were used during the life of the system;
most other specifications, however, remained unchanged.
Because IBM no longer markets the PC system, and because of
the PC's relatively limited expansion capability and power,
the standard PC is obsolete by most standards.
The system unit supports only floppy
disk drives unless the power supply is upgraded or an
expansion chassis is used to house the hard disk externally.
IBM never offered an internal hard disk for the PC, but many
third-party companies stepped in to fill this void with
upgrades. The system unit included many configurations with
single or dual floppy disk drives. Early on, one version even
was available with no disk drives, and others used
single-sided floppy drives.
The PC motherboard was based on the
16-bit Intel 8088 microprocessor and included the Microsoft
Cassette BASIC language built into ROM. For standard memory,
the PC offered configurations with as little as 16K of RAM
(when the system was first announced) and as much as 256K on
the motherboard. Two motherboard designs were used. Systems
sold before March 1983 had a motherboard that supported a
maximum of only 64K of RAM, and later systems supported a
maximum of 256K on the motherboard. In either case, you added
more memory (as much as 640K) by installing memory cards in
the expansion slots.
The first bank of memory chips in every
PC is soldered to the motherboard. Soldered memory is reliable
but not conducive to easy servicing because it prevents you
from easily exchanging failing memory chips located in the
first bank. The chips must be unsoldered and the defective
chip replaced with a socket so that a replacement can be
plugged in. When IBM services the defective memory, IBM
advises you to exchange the entire motherboard. Considering
today's value of these systems, replacing the mother-board
with one of the many compatible motherboards on the market may
be a better idea. Repairing the same defective memory chip in
the XT system is much easier because all memory in an XT is
socketed.
The only disk drive available from IBM
for the PC is a double-sided (320 or 360K) floppy disk drive.
You can install a maximum of two drives in the system unit by
using IBM-supplied drives, or four using half-height
third-party drives and mounting brackets.
The system unit has five slots that
support expansion cards for additional devices, features, or
memory. All these slots support full-length adapter cards. In
most configurations, the PC included at least a floppy disk
controller card. You need a second slot for a monitor adapter,
which leaves three slots for adapter cards.
All models of the PC have a fan-cooled,
63.5-watt power supply. This low-output power supply doesn't
support much in the way of system expansion, especially
power-hungry items such as hard disks. Usually, this
low-output supply must be replaced by a higher-output unit,
such as the one used in the XT. Figure 23.1 shows an interior
view of a PC system unit.
An 83-key keyboard with an adjustable
typing angle is standard equipment on the PC. The keyboard is
attached to the rear of the system unit by a six-foot coiled
cable. Figure 23.2 shows the back panel of the PC.
Most model configurations of the PC
system unit included these major functional components:
- Intel 8088
microprocessor
- One or two 360K floppy
drives
- ROM-based diagnostics
(POST)
- A 63.5-watt power
supply
- BASIC language interpreter in
ROM
- Five I/O expansion
slots
- 256K of dynamic RAM
- Socket for the 8087 math
coprocessor
- Floppy disk controller
PC Models and
Features
Although several configurations of the
IBM PC were available before March 1983, only two models were
available after that time. The later models differ only in the
number of floppy drives: one or two. IBM designated these
models as follows:
- IBM PC 5150 Model 166. 256K
RAM, one 360K drive.
- IBM PC 5150 Model 176. 256K
RAM, two 360K drives.
The IBM PC was never available with a
factory-installed hard disk (XT systems came with hard disks),
primarily because the system unit had limited room for
expansion and offered few resources with which to work. After
IBM started selling XTs with only floppy disk drives (on April
2, 1985), the PC essentially became obsolete. The XT offered
much more for virtually the same price, so investing in a PC
after the XT introduction was questionable.
FIG.
23.1 The IBM PC interior
view.
FIG.
23.2 The IBM PC rear
view.
IBM finally officially withdrew the PC
from the market on April 2, 1987. IBM's plans for the system
became obvious when the company didn't announce a new model
with the enhanced keyboard, as it did with other IBM systems.
In retrospect, it is amazing that the system was sold over a
period of nearly six years with few changes!
Table 23.1 shows the part numbers for
the IBM PC system units and options.
Table 23.1 IBM PC Models
and Part Numbers
Description |
Number |
PC system unit, 256K, one double-sided
drive |
5150166 |
PC system unit, 256K, two double-sided
drives |
5150176 |
Options |
Number |
PC expansion-unit Model 001 with 10M hard
disk |
5161001 |
Double-sided disk drive |
1503810 |
8087 math coprocessor option |
1501002 |
BIOS update kit (10/27/82 BIOS) |
1501005 |
With some creative purchasing, you
could make a usable system of a base PC by adding the
requisite components, such as a full 640K of memory as well as
hard disk and floppy drives. Only you can decide when your
money is better invested in a new system.
Before you think of expanding a PC
beyond even a simple configuration, and to allow for
compatibility and reliability, you must address the following
two major areas:
- ROM BIOS level
(version)
- 63.5-watt power supply
In most cases, the low output power
supply is the most critical issue because all PCs sold after
March 1983 already had the latest ROM BIOS. If you have an
earlier PC system, you also must upgrade the ROM because the
early versions lack some required capabilities, in particular
the ability to scan the memory range C0000-DFFFF in the Upper
Memory Area (UMA) for adapter card ROMs.
PC BIOS
Versions
There have been three different BIOS
versions used in the IBM PC. They can be identified by their
date and summarized as follows:
- April 24, 1981: The first PC BIOS
version would only support a maximum of 544K of RAM, plus it
would not scan the UMA for adapter card ROMs, such as are
found on EGA/VGA video adapters, hard disk controllers, and
SCSI adapters. This BIOS is very rare, and any such machine
is almost a collector's item as it represents one of the
first PCs ever made!
- October 19, 1981: The second PC BIOS
has the same 544K RAM and UMA scan limitations as the first
BIOS, but it does fix a couple of minor display bugs. Even
this BIOS is not very common.
- October 27, 1982: The third and
final PC BIOS has support for a full 640K of base RAM plus
the necessary UMA scan to support adapter cards with ROMs on
them. To be useful at all, a PC must have this BIOS
revision. If your PC BIOS is one of the older two versions,
note that IBM sells a BIOS update kit under part number
1501005.
Table 23.2 Lists the different IBM
Family/1 (PC, XT, and AT) BIOS versions. It also shows the ID,
Submodel, and Revision bytes that can be determined by a
software function call Int 15h, C0 = Return System Configuration Parameters
Some of the systems such as the PC and
earlier XT and AT systems only supports the ID byte; the
submodel and revision bytes had not been established when
those systems were developed. The table also shows the number
of drive types supported in the AT and XT-286 systems BIOS.
Table 23.2 IBM Family/1
(PC, XT, AT) System BIOS Dates
System |
CPU |
Speed |
BIOS Date |
ID, Submodel, Revision |
BIOS Drive Types |
PC |
8088 |
4.77MHz |
04/24/81 |
FF - - |
- |
PC |
8088 |
4.77MHz |
10/19/81 |
FF - - |
- |
PC |
8088 |
4.77MHz |
10/27/82 |
FF - - |
- |
PCjr |
8088 |
4.77MHz |
06/01/83 |
FD - - |
- |
PC-XT, PPC |
8088 |
4.77MHz |
11/08/82 |
FE - - |
- |
PC-XT |
8088 |
4.77MHz |
01/10/86 |
FB 00 01 |
- |
PC-XT |
8088 |
4.77MHz |
05/09/86 |
FB 00 02 |
- |
PC Convertible |
80C8 |
4.77MHz |
09/13/85 |
F9 00 00 |
- |
PC-AT |
286 |
6MHz |
01/10/84 |
FC - - |
15 |
PC-AT |
286 |
6MHz |
06/10/85 |
FC 00 01 |
23 |
PC-AT |
286 |
8MHz |
11/15/85 |
FC 01 00 |
23 |
PC-XT 286 |
286 |
6MHz |
04/21/86 |
FC 02 00 |
24 | The ID, Submodel, and Revision byte numbers
are in hexadecimal.
- = This feature is not
supported. The BIOS date is stored in all PC compatible
systems at memory address FFFF5h. To display the date of your
BIOS, a simple DEBUG command can be used to view this
address. DEBUG is a command program supplied with
MS-DOS. At the DOS prompt, execute the following commands to
run DEBUG, display the date stored in your BIOS, and
then exit back to DOS: C:\>DEBUG
-D FFFF:5 L 8
FFFF:0000 30 31 2F-32 32 2F 39 37 01/22/97
-Q
In this example, the system queried
shows a BIOS date of 01/22/97.
PC Technical
Specifications
Technical information for the Personal
Computer system and keyboard is described in this section.
Here, you find information about the system architecture,
memory configurations and capacities, standard system
features, disk storage, expansion slots, keyboard
specifications, and physical and environmental specifications.
This kind of information may be useful in determining what
parts you need when you are upgrading or repairing these
systems. Figure 23.3 shows the layout and components on the PC
motherboard.
FIG.
23.3 The IBM PC
motherboard.
System Architecture
Microprocessor |
8088 |
Clock speed |
4.77MHz |
Bus type |
ISA (Industry Standard
Architecture) |
Bus width |
8-bit |
Interrupt levels |
8 (6 usable) |
Type |
Edge-triggered |
Shareable |
No |
DMA channels |
4 (3 usable) |
Bus masters supported |
No |
Upgradable processor complex |
No |
Memory |
|
Standard on system board |
16K, 64K, or 256K |
Maximum on system board |
256K |
Maximum total memory |
640K |
Memory speed (ns) and type |
200ns dynamic RAM chips |
System board memory-socket type |
16-pin DIP |
Number of memory-module sockets |
27 (3 banks of 9 chips) |
Memory used on system board |
27 16Kx1-bit or 64Kx1-bit DRAM chips in 3
banks of 9, one soldered bank of 9 16Kx1-bit or
64Kx1-bit chips |
Memory cache controller |
No |
Wait states: |
|
System board |
1 |
Adapter |
1 |
Standard Features |
|
ROM size |
40K |
ROM shadowing |
No |
Optional math coprocessor |
8087 |
Coprocessor speed |
4.77MHz |
Standard graphics |
None standard |
RS232C serial ports |
None standard |
UART chip used |
NS8250B |
Maximum speed (bits per second) |
9,600 bps |
Maximum number of ports supported |
2 |
Pointing device (mouse) ports |
None standard |
Parallel printer ports |
None standard |
Bi-directional |
No |
Maximum number of ports supported |
3 |
CMOS real-time clock (RTC) |
No |
CMOS RAM |
None |
Disk Storage |
|
Internal disk and tape drive bays |
2 full-height |
Number of 3 1/2-/5 1/4-inch bays |
0/2 |
Standard floppy drives |
1x360K |
Optional floppy drives: |
|
5 1/4-inch 360K |
Optional |
5 1/4-inch 1.2M |
No |
3 1/2-inch 720K |
Optional |
3 1/2-inch 1.44M |
No |
3 1/2-inch 2.88M |
No |
Hard disk controller included |
None |
Expansion Slots |
|
Total adapter slots |
5 |
Number of long and short slots |
5/0 |
Number of 8-/16-/32-bit slots |
5/0/0 |
Available slots (with video) |
3 |
Keyboard Specifications |
|
101-key Enhanced keyboard |
No, 83-key |
Fast keyboard speed setting |
No |
Keyboard cable length |
6 feet |
Physical Specifications |
|
Footprint type |
Desktop |
Dimensions: |
|
Height |
5.5 inches |
Width |
19.5 inches |
Depth |
16.0 inches |
Weight |
25 pounds |
Environmental Specifications |
|
Power-supply output |
63.5 watts |
Worldwide (110/60,220/50) |
No |
Auto-sensing/switching |
No |
Maximum current: |
|
104-127 VAC |
2.5 amps |
Operating range: |
|
Temperature |
60-90° F |
Relative humidity |
8-80 percent |
Maximum operating altitude |
7,000 feet |
Heat (BTUs/hour) |
505 |
Noise (Average db, operating, 1m) |
43 |
FCC classification |
Class B |
Tables 23.3 and 23.4 show the Switch
Settings for the PC (and XT) motherboard. The PC has two
eight-position switch blocks (Switch Block 1 and Switch Block
2), whereas the XT has only a single Switch Block 1. The PC
used the additional switch block to control the amount of
memory the system would recognize, and the XT automatically
counted up the memory amount.
Table 23.3 IBM PC/XT
Motherboard Switch Settings
SWITCH BLOCK 1 (PC and
XT) |
|
Switch 1 |
IBM PC Function (PC Only): |
Off |
Boot From Floppy Drives |
On |
Do Not Boot From Floppy Drives |
Switch 1 |
IBM XT Function (XT Only): |
Off |
Normal POST (Power-On Self Test) |
On |
Continuous Looping POST |
Switch 2 |
Math Coprocessor (PC/XT): |
Off |
Installed |
On |
Not Installed |
Switch 4 |
Installed Motherboard Memory
(PC/XT): |
On |
On |
Bank 0 only |
Off |
On |
Banks 0 and 1 |
On |
Off |
Banks 0, 1 and 2 |
Off |
Off |
All 4 Banks |
Switch 5 |
Switch 6 |
Video Adapter Type (PC/XT): |
Off |
Off |
Monochrome (MDA) |
Off |
On |
Color (CGA) - 40x25 mode |
On |
Off |
Color (CGA) - 80x25 mode |
On |
On |
Any Video Card w/onboard BIOS
(EGA/VGA) |
Switch 7 |
Switch 8 |
Number of Floppy Drives
(PC/XT): |
On |
On |
1 floppy drive |
Off |
On |
2 floppy drives |
On |
Off |
3 floppy drives |
Off |
Off |
4 floppy drives |
Table 23.4 Switch Blocks 2
(PC Only) Memory Settings
|
Switch Number (Switch Block
2, PC Only) |
Memory |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
16K |
On |
On |
On |
On |
On |
Off |
Off |
Off |
32K |
On |
On |
On |
On |
On |
Off |
Off |
Off |
48K |
On |
On |
On |
On |
On |
Off |
Off |
Off |
64K |
On |
On |
On |
On |
On |
Off |
Off |
Off |
96K |
Off |
On |
On |
On |
On |
Off |
Off |
Off |
128K |
On |
Off |
On |
On |
On |
Off |
Off |
Off |
160K |
Off |
Off |
On |
On |
On |
Off |
Off |
Off |
192K |
On |
On |
Off |
On |
On |
Off |
Off |
Off |
224K |
Off |
On |
Off |
On |
On |
Off |
Off |
Off |
256K |
On |
Off |
Off |
On |
On |
Off |
Off |
Off |
288K |
Off |
Off |
Off |
On |
On |
Off |
Off |
Off |
320K |
On |
On |
On |
Off |
On |
Off |
Off |
Off |
352K |
Off |
On |
On |
Off |
On |
Off |
Off |
Off |
384K |
On |
Off |
On |
Off |
On |
Off |
Off |
Off |
416K |
Off |
Off |
On |
Off |
On |
Off |
Off |
Off |
448K |
On |
On |
Off |
Off |
On |
Off |
Off |
Off |
480K |
Off |
On |
Off |
Off |
On |
Off |
Off |
Off |
512K |
On |
Off |
Off |
Off |
On |
Off |
Off |
Off |
544K |
Off |
Off |
Off |
Off |
On |
Off |
Off |
Off |
576K |
On |
On |
On |
On |
Off |
Off |
Off |
Off |
608K |
Off |
On |
On |
On |
Off |
Off |
Off |
Off |
640K |
On |
Off |
On |
On |
Off |
Off |
Off |
Off |
An Introduction
to the PC Convertible (5140)
IBM marked its entry into the laptop
computer market on April 2, 1986, by introducing the IBM 5140
PC Convertible. The system superseded the 5155 Portable PC
(IBM's transportable system), which was discontinued. The IBM
5140 system wasn't a very successful laptop system. Other
laptops offered more disk storage, higher processor speeds,
more readable screens, lower cost, and more compact cases,
which pressured IBM to improve the Convertible. Because the
improvements were limited to the display, however, this system
never gained respect in the marketplace. It is significant in
two respects; the first is that it marked IBM's entry into the
laptop and notebook portable system market, a market they have
tremendous success in today with the ThinkPad systems. The
second is that the Convertible was the first IBM PC system
supplied with 3 1/2-inch floppy drives.
The PC Convertible was available in two
models. The Model 2 had a CMOS 80C88 4.77MHz microprocessor,
64K of ROM, 256K of Static RAM, an 80-columnx25-line
detachable liquid crystal display (LCD), two 3 1/2-inch floppy
disk drives, a 78-key keyboard, an AC adapter, and a battery
pack. Also included were software programs called Application
Selector, SystemApps, Tools, Exploring the IBM PC Convertible,
and Diagnostics. The Model 22 is the same basic computer as
the Model 2 but with the diagnostics software. You can expand
either system to 512K of RAM by using 128K RAM memory cards,
and you can include an internal 1,200 bps modem in the system
unit. With aftermarket memory expansion, the computers can
reach 640K.
Although the unit was painfully slow at
4.77MHz, one notable feature is the use of Static memory chips
for the system's RAM. Static RAM does not require the refresh
signal that normal Dynamic RAM (DRAM) requires, which would
normally require about 7 percent of the processor's time in a
standard PC or XT system. This means that the Convertible is
about 7 percent faster than an IBM PC or XT, even though they
all operate at the same clock speed of 4.77MHz. Because of the
increased reliability of the Static RAM (compared to DRAM)
used in the Convertible, as well as the desire to minimize
power consumption, none of the RAM in the Convertible is
parity checked.
At the back of each system unit is an
extendable bus interface. This 72-pin connector enables you to
attach the following options to the base unit: a printer, a
serial or parallel adapter, and a CRT display adapter. Each
feature is powered from the system unit. The CRT display
adapter operates only when the system is powered from a
standard AC adapter. A separate CRT display or a television
set attached through the CRT display adapter requires a
separate AC power source.
Each system unit includes a detachable
LCD. When the computer is not mobile, the LCD screen can be
replaced by an external monitor. When the LCD is latched in
the closed position, it forms the cover for the keyboard and
floppy disk drives. Because the LCD is attached with a
quick-disconnect connector, you can remove it easily to place
the 5140 system unit below an optional IBM 5144 PC Convertible
monochrome or IBM 5145 PC Convertible color display. During
the life of the Convertible, IBM offered three different LCD
displays. The first display was a standard LCD, which suffered
from problems with contrast and readability. Due to
complaints, IBM then changed the LCD to a Super Twisted type
LCD display, which had much greater contrast. Finally, in the
third LCD, IBM added a fluorescent backlight to the Super
Twisted LCD display, which not only offered greater contrast,
but made the unit usable in low light situations.
The PC Convertible system unit has
these standard features:
- Complementary Metal-Oxide
Semiconductor (CMOS) 80C88 4.77 MHz
micro-processor
- Two 32K CMOS ROMs containing these
items:
- POST (Power On Self Test) of
system components
- BIOS (basic input-output system)
support
- BASIC language
interpreter
- 256K CMOS Static RAM (expandable to
512K)
- Two 3 1/2-inch 720K (formatted)
floppy drives
- An 80-columnx25-line detachable LCD
panel (graphics modes: 640x200 resolution and 320x200
resolution)
- LCD controller
- 16K RAM display
buffer
- 8K LCD font RAM
- Adapter for optional printer
(#4010)
- Professional keyboard (78
keys)
- AC adapter
- Battery pack
The system-unit options for the 5140
are shown in this list:
- 128K Static RAM memory card
(#4005)
- Printer (#4010)
- Serial/parallel adapter
(#4015)
- CRT display adapter
(#4020)
- Internal modem
(#4025)
- Printer cable (#4055)
- Battery charger
(#4060)
- Automobile power adapter (#4065)
The following two optional displays
were available for the PC Convertible:
- IBM 5144 PC Convertible Monochrome
Display Model 1
- IBM 5145 PC Convertible Color
Display Model 1
PC Convertible
Specifications and Highlights
This section lists some technical
specifications for the IBM 5140 PC Convertible system. The
weights of the unit and options are listed because weight is
an important consideration when you carry a laptop system.
Figure 23.4 shows the PC Convertible mother-board components
and layout.
Dimensions |
|
Depth: |
360 mm (14.17 inches) 374 mm (14.72
inches) including handle |
Width: |
309.6 mm (12.19 inches) 312 mm (12.28
inches) including handle |
Height: |
67 mm (2.64 inches) 68 mm (2.68
inches) including footpads |
Weight |
|
Models 2 and 22 (including battery) |
5.5 kg (12.17 pounds) |
128K/256K memory card |
40 g (1.41 ounces) |
Printer |
1.6 kg (3.50 pounds) |
Serial/parallel adapter |
470 g (1.04 pounds) |
CRT display adapter |
630 g (1.40 pounds) |
Internal modem |
170 g (6 ounces) |
Printer cable |
227 g (8 ounces) |
Battery charger |
340 g (12 ounces) |
Automobile power adapter |
113 g (4 ounces) |
5144 PC Convertible monochrome display |
7.3 kg (16 pounds) |
5145 PC Convertible color display |
16.9 kg (37.04
pounds) |
FIG.
23.4 The PC Convertible
motherboard.
To operate the IBM 5140 PC Convertible
properly, you must have PC DOS version 3.2 or later. Previous
DOS versions aren't supported because they don't support the
720K floppy drive.
PC Convertible
Models and Features
This section covers the options and
special features available for the PC Convertible. Several
kinds of options were available, from additional memory to
external display adapters, serial/parallel ports, modems, and
even printers.
Memory Cards
A 128K or 256K memory card expands the
base memory in the system unit. You can add two of these
cards, for a system-unit total of 640K with one 256K card and
one 128K card.
Optional Printer
A special printer is available that
attaches to the back of the system unit or to an optional
printer-attachment cable for adjacent printer operation. The
printer's intelligent, microprocessor-based, 40cps, non-impact
dot-matrix design makes it capable of low-power operation. The
printer draws power from and is controlled by the system unit.
Standard ASCII 96-character, upper- and lowercase character
sets were printed with a high-resolution, 24-element print
head. A mode for graphics capability is provided also. You can
achieve near-letter-quality printing by using either a thermal
transfer ribbon on smooth paper or no ribbon on heat-sensitive
thermal paper.
A special printer cable is available
that is 22 inches (0.6 meters) long with a custom 72-pin
connector attached to each end. With this cable, you can
operate the Convertible printer when it is detached from the
system unit and place the unit for ease of use and
visibility.
Serial/Parallel
Adapter
A serial/parallel adapter attaches to
the back of the system unit, a printer, or other feature
module attached to the back of the system unit. The adapter
provides an RS-232C asynchronous communications interface and
a parallel printer interface, both compatible with the IBM
personal computer asynchronous communications adapter and the
IBM personal computer parallel printer adapter.
CRT Display Adapter
A CRT display adapter attaches to the
back of the system unit, printer, or other feature module
attached to the back of the system unit. This adapter enables
you to connect a separate CRT display to the system, such as
the PC Convertible monochrome display or PC Convertible color
display. By using optional connectors or cables, you can use
the CRT display adapter also to attach a standard Color
Graphics Adapter (CGA) monitor. Because composite video output
is available, you also can use a standard television
set.
Internal Modems
IBM offered two different internal
modems for the Convertible. Both run Bell 212A (1,200 bps) or
Bell 103A (300 bps) protocols. The modems came as a complete
assembly, consisting of two cards connected by a cable. The
entire assembly is installed inside the system unit. The
original first design modem was made for IBM by Novation, and
did not follow the Hayes standard for commands and protocols.
This rendered the modem largely incompatible with popular
software designed to use the Hayes command set. Later, IBM
changed the modem to one that was fully Hayes compatible; this
resolved the problems with software. IBM never introduced a
modem faster than 1,200 bps for the Convertible. Fortunately,
you can operate a standard external modem through the serial
port, although you lose the convenience of having it built
in.
Battery Charger/Auto Power
Adapter
The battery charger is a 110-volt input
device that charges the system's internal batteries. It does
not provide sufficient power output for the system to operate
while the batteries are being charged. An available automobile
power adapter plugs into the cigarette-lighter outlet in a
vehicle with a 12-volt, negative-ground electrical system. You
can use the system while the adapter also charges the
Convertible's battery
Optional Displays
The 5144 PC Convertible monochrome
display is a 9-inch (measured diagonally) composite video
display attached to the system unit through the CRT display
adapter. It comes with a display stand, an AC power cord, and
a signal cable that connects the 5144 to the CRT display
adapter. This display does not resemble--and is not compatible
with--the IBM monochrome display for larger PC systems. The
CRT adapter emits the same signal as the one supplied by the
Color Graphics Adapter for a regular PC. This display is
functionally equivalent to the display on the IBM Portable
PC.
The 5145 PC Convertible color display
is a 13-inch color display attached to the system unit through
the CRT display adapter. It comes with a display stand, an AC
power cord, a signal cable that connects the 5145 to the CRT
display adapter, and a speaker for external audio output. The
monitor is a low-cost unit compatible with the standard IBM
CGA display.
Table 23.5 shows the part numbers of
the IBM Convertible system units.
Table 23.5 IBM Convertible
Part Numbers
5140 PC Convertible System
Units |
Number |
Two drives, 256K with system
applications |
5140002 |
Two drives, 256K without system
applications |
5140022 |
An Introduction
to the XT (5160)
Introduced March 8, 1983, the PC XT
with a built-in 10M hard disk (originally standard, later
optional) caused a revolution in personal computer
configurations. At the time, having even a 10M hard disk was
something very special. XT stands for eXTended.
IBM chose this name because the IBM PC XT system includes many
features not available in the standard PC. The XT has eight
slots, allowing increased expansion capabilities; greater
power-supply capacity; completely socketed memory;
motherboards that support memory expansion to 640K without
using an expansion slot; and optional hard disk drives. To
obtain these advantages, the XT uses a different motherboard
circuit design than the PC.
The system unit was available in
several models, with a variety of disk drive configurations:
one 360K floppy disk drive, two 360K floppy disk drives, one
floppy disk and one hard disk drive, or two floppy disk drives
and one hard disk drive. The floppy disk drives were
full-height drives in the earlier models, and half-height
drives in more recent models. With the four available drive
bays, IBM had standard configurations with two floppy drives
and a single hard disk, with room for a second hard disk,
provided all half-height units were used.
IBM offered only 10M and 20M
full-height hard disks. In some cases, they also installed
half-height hard disks, but they were always installed in a
bracket and cradle assembly that took up the equivalent space
of a full-height drive. If you wanted half-height hard disks
(to install two of them stacked, for example), you had to use
non-IBM supplied drives or modify the mounting of the IBM
supplied half-height unit so that two could fit. Most
aftermarket sources for hard disks had mounting kits that
would work.
IBM also used double-sided (320/360K)
floppy disk drives in full- or half-height configurations. A 3
1/2-inch 720K floppy disk drive was available in more recent
models. The 3 1/2-inch drives were available in a normal
internal configuration or as an external device. You could
install a maximum of two floppy disk drives and one hard disk
drive in the system unit, using IBM-supplied drives. With
half-height hard disks, you could install two hard drives in
the system unit.
The XT is based on the same 8- and
16-bit Intel 8088 microprocessor (the CPU has 16-bit registers
but only an 8-bit data bus) as the PC and runs at the same
clock speed. Operationally, the XT systems are identical to
the PC systems except for the hard disk. All models have at
least one 360K floppy disk drive and a keyboard. For standard
memory, the XT offers 256K or 640K on the main board. The hard
disk models also include a serial adapter.
The system unit has eight slots that
support cards for additional devices, features, or memory. Two
of the slots support only short option cards because of
physical interference from the disk drives. The XT has at
least a disk drive adapter card in the floppy-disk-only
models, and a hard disk controller card and serial adapter in
the hard disk models. Either five or seven expansion slots
(depending on the model) therefore are available. Figure 23.5
shows the interior of an XT.
FIG.
23.5 The IBM PC XT
interior.
All XT models include a heavy-duty,
fan-cooled, 130-watt power supply to support the greater
expansion capabilities and disk drive options. The power
supply has more than double the capacity of the PC's supply,
and can easily support hard disk drives as well as the full
complement of expansion cards.
An 83-key keyboard was standard
equipment with the early XT models, but was changed to an
enhanced 101-key unit in the more recent models. The keyboard
is attached to the system unit by a six-foot coiled
cable.
All models of the PC XT system unit
contain these major functional components:
- Intel 8088
microprocessor
- ROM-based diagnostics
(POST)
- BASIC language interpreter in
ROM
- 256K or 640K of dynamic
RAM
- Floppy disk
controller
- One 360K floppy drive (full- or
half-height)
- 10M or 20M hard disk drive with
interface (enhanced models)
- Serial interface (enhanced
models)
- Heavy-duty, 135-watt power
supply
- Eight I/O expansion
slots
- Socket for 8087 math coprocessor
XT Models and
Features
The XT was available in many different
model configurations, but originally only one model was
available. This model included a 10M hard disk, marking the
first time that a hard disk was standard equipment in a
personal computer and was properly supported by the operating
system and peripherals. This computer helped change the
industry standard for personal computers from normally having
one or two floppy disk drives only to now including one or
more hard disks.
Today, most people wouldn't consider a
PC to be even remotely usable without a hard disk. The
original XT was expensive, however, and buyers couldn't
unbundle, or delete, the hard disk from the system at purchase
time for credit and add it later. This fact distinguished the
XT from the PC and misled many people to believe that the only
difference between the two computers was the hard disk. People
who recognized and wanted the greater capabilities of the XT
without the standard IBM hard disk unfortunately had to wait
for IBM to sell versions of the XT without the hard disk
drive.
The original Model 087 of the XT
included a 10M hard disk, 128K of RAM, and a standard serial
interface. IBM later increased the standard memory in all PC
systems to 256K. The XT reflected the change in Model 086,
which was the same as the preceding 087 except for a standard
256K of RAM.
On April 2, 1985, IBM finally
introduced new models of the XT without the standard hard
disk. Designed for expansion and configuration flexibility,
the new models enabled you to buy the system initially at a
lower cost and add your own hard disk later. The XT therefore
could be considered in configurations that previously only the
original PC could fill. The primary difference between the PC
and the XT is the XT's expansion capability, provided by the
larger power supply, eight slots, and better memory layout.
These models cost only $300 more than equivalent PCs,
rendering the original PC no longer a viable
option.
The extra expense of the XT can be
justified with the first power-supply replacement you make
with an overworked PC. The IBM PC XT is available in two
floppy disk models:
- 5160068 XT with one full-height 360K
disk drive
- 5160078 XT with two full-height 360K
disk drives
Both these models have 256K of memory
and use the IBM PC XT motherboard, power supply, frame, and
cover. The serial (asynchronous communications) port adapter
isn't included as a standard feature with these
models.
IBM introduced several more models of
the PC XT on April 2, 1986. These models were significantly
different from previous models. The most obvious difference,
the 101-key enhanced keyboard, was standard with these newer
computers. A 20M (rather than 10M) hard disk and one or two
half-height floppy disk drives were included. The new
half-height floppy disk drives allow for two drives in the
space that previously held only one floppy drive. With two
drives, backing up floppy disks became easy. A new 3 1/2-inch
floppy disk drive, storing 720K for compatibility with the PC
Convertible laptop computer, was released also. These newer XT
system units were configured with a slightly different memory
layout, allowing for 640K of RAM on the motherboard without an
expansion slot. This feature conserves power, improves
reliability, and lowers the cost of the system.
One 5 1/4-inch, half-height, 360K
floppy disk drive and 256K of system-board memory was standard
with the XT Models 267 and 268. Models 277 and 278 have a
second 5 1/4-inch floppy disk drive. Models 088 and 089 were
expanded PC XTs with all the standard features of the Models
267 and 268, a 20M hard disk, a 20M fixed disk drive adapter,
a serial port adapter, and an additional 256K of system-board
memory--a total of 512K.
The following list shows the highlights
of these new models:
- Enhanced keyboard standard on Models
268, 278, and 089; 101 keys, and no status LEDs (XT
interface cannot drive LEDs)
- Standard PC XT keyboard on Models
267, 277, and 088
- More disk capacity
(20M)
- Standard 5 1/4-inch, half-height,
360K floppy drive
- Available 3 1/2-inch, half-height,
720K floppy drive
- Capacity for four half-height
storage devices within the system unit
- Capacity to expand to 640K bytes
memory on system board without using expansion slots
These newest XT models have an
extensively changed ROM BIOS. The new BIOS is 64K and is
internally similar to the BIOS found in ATs. The ROM includes
support for the new keyboard and 3 1/2-inch floppy disk
drives. The POST also was enhanced.
The new XTs were originally
incompatible in some respects with some software programs.
These problems centered on the new 101-key enhanced keyboard
and the way the new ROM addressed the keys. These problems
weren't major and were solved quickly by the software
companies.
Seeing how much IBM changed the
computer without changing the basic motherboard design is
interesting. The ROM is different, and the board now could
hold 640K of memory without a card in a slot. The memory trick
is a simple one. IBM designed this feature into the board
originally and chose to unleash it with these models of the
XT.
During the past several years, I have
modified many XTs to have 640K on the mother-board, using a
simple technique designed into the system by IBM. A jumper and
chip added to the motherboard can alter the memory addressing
in the board to enable the system to recognize 640K. The new
addressing is set up for 256K chips, installed in two of the
four banks. The other two banks of memory contain 64K chips--a
total of 640K.
Complete instructions for how to
install 640K of memory on the XT motherboard can be found on
the CD which accompanies this book.
XT BIOS
Versions
There have been three different BIOS
versions used in the IBM PC-XT. They can be identified by
their date and summarized as follows:
- November 8, 1982: The original XT
BIOS had all of the features of the latest 10/27/82 PC BIOS,
including 640K base memory and UMA scan support. This BIOS
version was also used in the XT motherboards found in the
IBM Portable PC (PPC).
- January 10, 1986: The second
revision XT BIOS added support for the 101-key Enhanced
keyboard, plus full support for 3 1/2-inch 720K floppy
drives.
- May 9, 1986: This final revision
contained some fixes for minor keyboard bugs related mainly
to the enhanced keyboard.
Table 23.1 lists the different IBM
Family/1 (PC, XT, and AT) BIOS versions. It also shows the ID,
Submodel, and Revision bytes that can be determined by the
software function call Int 15h, C0 = Return System Configuration Parameters
Some of the systems, such as the PC and
earlier XT and AT systems, only supports the ID byte; the
submodel and revision bytes had not been established when
those systems were developed. The table also shows the number
of drive types supported in the AT and XT-286 systems
BIOS.
The BIOS date is stored in all PC
compatible systems at memory address FFFF5h. To display the
date of your BIOS, a simple DEBUG command can be used
to view this address. DEBUG is a command program
supplied with MS-DOS. At the DOS prompt, execute the following
commands to run DEBUG, display the date stored in
your BIOS, and then exit to DOS: C:\>DEBUG
-D FFFF:5 L 8
FFFF:0000 30 31 2F-32 32 2F 39 37 01/22/97
-Q
In this example, the system queried
shows a BIOS date of 01/22/97.
XT Technical
Specifications
Technical information for the XT
system, described in this section, provides information about
the system architecture, memory configurations and capacities,
standard system features, disk storage, expansion slots,
keyboard specifications, and also physical and environmental
specifications. Figure 23.6 shows the layout and components on
the XT motherboard.
FIG.
23.6 The XT motherboard.
System Architecture |
|
|
Microprocessor |
8088 |
|
Clock speed |
4.77MHz |
|
Bus type |
ISA (Industry Standard Architecture) |
|
Bus width |
8-bit |
|
Interrupt levels |
8 (6 usable) |
|
Type |
Edge-triggered |
|
Shareable |
No |
|
DMA channels |
4 (3 usable) |
|
Bus masters supported |
No |
|
Upgradable processor complex |
No |
|
Memory |
|
|
Standard on system board |
256K or 640K |
|
Maximum on system board |
256K or 640K |
|
Maximum total memory |
640K |
|
Memory speed (ns) and type |
200ns dynamic RAM chips |
|
System board memory-socket type |
16-pin DIP |
|
Number of memory-module sockets |
36 (4 banks of 9) |
|
Memory used on system board |
36 64Kx1-bit DRAM chips in 4 banks of 9,
or 2 banks of 9 256Kx1-bit and 2 banks of 9 64Kx1-bit
chips |
|
Memory cache controller |
No |
|
Wait states: |
|
|
System board |
1 |
|
Adapter |
1 |
|
Standard Features |
|
|
ROM size |
40K or 64K |
|
ROM shadowing |
No |
|
Optional math coprocessor |
8087 |
|
Coprocessor speed |
4.77MHz |
|
Standard graphics |
None standard |
|
RS232C serial ports |
1 (some models) |
|
UART chip used |
NS8250B |
|
Maximum speed (bits per second) |
9,600 bps |
|
Maximum number of ports supported |
2 |
|
Pointing device (mouse) ports |
None standard |
|
Parallel printer ports |
1 (some models) |
|
Bi-directional |
No |
|
Maximum number of ports supported |
3 |
|
CMOS real-time clock (RTC) |
No |
|
CMOS RAM |
None |
|
Disk Storage |
|
|
Internal disk and tape drive bays |
2 full-height or 4 half-height |
|
Number of 3 1/2 or 5 1/4-inch bays |
0/2 or 0/4 |
|
Standard floppy drives |
1x360K |
|
Optional floppy drives: |
|
|
5 1/4-inch 360K |
Optional |
|
5 1/4-inch 1.2M |
No |
|
3 1/2-inch 720K |
Optional |
|
3 1/2-inch 1.44M |
No |
|
3 1/2-inch 2.88M |
No |
|
Hard disk controller included: |
ST-506/412 (Xebec Model 1210) |
|
ST-506/412 hard disks available |
10/20M |
|
Drive form factor |
5 1/4-inch |
|
Drive interface |
ST-506/412 |
|
Drive capacity |
10M |
20M |
Average access rate (ms) |
85 |
65 |
Encoding scheme |
MFM |
MFM |
BIOS drive type number |
1 |
2 |
Cylinders |
306 |
615 |
Disk storage |
|
|
Heads |
4 |
4 |
Sectors per track |
17 |
17 |
Rotational speed (RPMs) |
3600 |
3600 |
Interleave factor |
6:1 |
6:1 |
Data transfer rate (kilobytes/second) |
85 |
85 |
Automatic head parking |
No |
No |
Expansion Slots |
|
|
Total adapter slots |
8 |
|
Number of long/short slots |
6/2 |
|
Number of 8-/16-/32-bit slots |
8/0/0 |
|
Available slots (with video) |
4 |
|
Keyboard Specifications |
|
|
101-key Enhanced keyboard |
Yes |
|
Fast keyboard speed setting |
No |
|
Keyboard cable length |
6 feet |
|
Physical Specifications |
|
|
Footprint type |
Desktop |
|
Dimensions: |
|
|
Height |
5.5 inches |
|
Width |
19.5 inches |
|
Depth |
16.0 inches |
|
Weight |
32 pounds |
|
Environmental Specifications |
|
|
Power-supply output |
130 watts |
|
Worldwide (110v/60Hz, 220v/50Hz) |
No |
|
Auto-sensing/switching |
No |
|
Maximum current: |
|
|
90-137 VAC |
4.2 amps |
|
Operating range: |
|
|
Temperature |
60-90 degrees F |
|
Relative humidity |
8-80 percent |
|
Maximum operating altitude |
7,000 feet |
|
Heat (BTUs/hour) |
717 |
|
Noise (Average db, operating, 1m) |
56 |
|
FCC classification |
Class B |
|
Table 23.6 shows the XT motherboard
switch settings. The XT motherboard uses a single
eight-position switch block to control various functions, as
detailed in the table.
Table 23.6 IBM PC/XT
Motherboard Switch Settings
SWITCH BLOCK 1 (PC and XT)
|
Switch 1 |
IBM PC Function (PC Only): |
|
Off |
Boot From Floppy Drives |
|
On |
Do Not Boot From Floppy Drives |
|
Switch 1 |
IBM XT Function (XT Only): |
|
Off |
Normal POST (Power-On Self Test) |
|
On |
Continuous Looping POST |
|
Switch 2 |
Math Coprocessor (PC/XT): |
|
Off |
Installed |
|
On |
Not Installed |
Switch 3 |
Switch 4 |
Installed Motherboard Memory
(PC/XT): |
On |
On |
Bank 0 only |
Off |
On |
Banks 0 and 1 |
On |
Off |
Banks 0, 1, and 2 |
Off |
Off |
All 4 Banks |
Switch 5 |
Switch 6 |
Video Adapter Type (PC/XT): |
Off |
Off |
Monochrome (MDA) |
Off |
On |
Color (CGA); 40x25 mode |
On |
Off |
Color (CGA); 80x25 mode |
On |
On |
Any Video Card w/onboard BIOS
(EGA/VGA) |
Switch 7 |
Switch 8 |
Number of Floppy Drives
(PC/XT): |
On |
On |
1 floppy drive |
Off |
On |
2 floppy drives |
On |
Off |
3 floppy drives |
Off |
Off |
4 floppy drives |
Table 23.7 shows the part numbers of
the XT system units.
Table 23.7 IBM XT Model
Part Numbers
Description |
Number |
XT system unit/83-key keyboard, 256K: |
|
one full-height 360K drive |
5160068 |
one half-height 360K drive |
5160267 |
two full-height 360K drives |
5160078 |
two half-height 360K drives |
5160277 |
XT system unit/101-key keyboard, 256K: |
|
one half-height 360K drive |
5160268 |
two half-height 360K drives |
5160278 |
XT system unit/83-key keyboard, 256K, one
serial, |
|
one full-height 360K drive, 10M hard
disk |
5160086 |
XT system unit/83-key keyboard, 640K, one
serial, |
|
one half-height 360K drive, 20M fixed
disk |
5160088 |
XT system unit/101-key keyboard, 640K,
one serial, |
|
one half-height 360K drive, 20M fixed
disk |
5160089 |
Option Numbers |
|
PC expansion-unit Model 002, 20M fixed
disk |
5161002 |
20M fixed disk drive |
6450326 |
20M fixed disk adapter |
6450327 |
10M fixed disk drive |
1602500 |
10M fixed disk adapter |
1602501 |
5 1/4-inch, half-height, 360K drive |
6450325 |
5 1/4-inch, full-height, 360K drive |
1503810 |
3 1/2-inch, half-height, 720K internal
drive |
6450258 |
3 1/2-inch, half-height, 720K external
drive |
2683190 |
8087 math coprocessor option |
1501002 |
Asynchronous serial adapter |
1502074 |
Enhanced Keyboard Accessories |
|
Clear keycaps (60) with paper inserts |
6341707 |
Blank light keycaps |
1351710 |
Blank dark keycaps |
1351728 |
Paper inserts (300) |
6341704 |
Keycap-removal tools (6) |
1351717 |
An Introduction
to the Portable PC
IBM introduced the Portable PC on
February 16, 1984. The IBM Portable PC, a "transportable"
personal computer, is a small suitcase-sized system that has a
built-in 9-inch, amber composite video monitor; one 5
1/4-inch, half-height floppy disk drive (with space for an
optional second drive); an 83-key keyboard; two adapter cards;
a floppy disk controller; and a CGA. The unit also has a
universal-voltage power supply capable of overseas operation
on 220-volt power. Figure 23.7 shows the Portable PC
exterior.
FIG.
23.7 The IBM Portable PC
The system board used in the IBM
Portable PC is the same board used in the original IBM XTs,
with 256K of memory. Because the XT motherboard was used,
eight expansion slots are available for the connection of
adapter boards, although only two slots can accept a
full-length adapter card due to internal space restrictions.
The power supply is basically the same as an XT's, with
physical changes for portability and a small amount of power
drawn to run the built-in monitor. In function and
performance, the Portable PC system unit has identical
characteristics to an equivalently configured IBM PC XT system
unit. Figure 23.8 shows the Portable PC interior
view.
IBM withdrew the Portable PC from the
market on April 2, 1986, a date that coincides with the
introduction of the IBM Convertible laptop PC. The Portable PC
is rare because not many were sold, although it compared to,
and in many ways was better than, the highly successful Compaq
Portable that was available at the time. The system was
largely misunderstood by the trade press and user community.
Most did not understand that the system was really a portable
XT and had more to offer than the standard IBM PC. Maybe if
IBM had called the system the Portable XT, it would have sold
better!
FIG.
23.8 The IBM Portable PC
interior.
The Portable PC system unit has these
major functional components:
- Intel 8088 4.77MHz
microprocessor
- ROM-based diagnostics
(POST)
- BASIC language interpreter in
ROM
- 256K of dynamic RAM
- Eight expansion slots (two long
slots, one 3/4-length slot, and five short
slots)
- Socket for 8087 math
coprocessor
- Color/Graphics Monitor
Adapter
- 9-inch, amber, composite video
monitor
- Floppy disk interface
- One or two half-height 360K floppy
drives
- 114-watt universal power supply
(115-230V, 50-60Hz)
- Lightweight 83-key
keyboard
- Enclosure with carrying
handle
- Carrying bag for the system unit
Seen previously, Figure 23.6 showed the
XT motherboard, which is also used in the Portable PC. The
following is the technical data for the Portable PC system:
System Architecture |
|
Microprocessor |
8088 |
Clock speed |
4.77MHz |
Bus type |
ISA (Industry Standard
Architecture) |
Bus width |
8-bit |
Interrupt levels |
8 (6 usable) |
Type |
Edge-triggered |
Shareable |
No |
DMA channels |
4 (3 usable) |
Bus masters supported |
No |
Upgradable processor complex |
No |
Memory |
|
Standard on system board |
256K |
Maximum on system board |
256K |
Maximum total memory |
640K |
Memory speed (ns) and type |
200ns dynamic RAM chips |
System board memory-socket type |
16-pin DIP |
Number of memory-module sockets |
36 (4 banks of 9) |
Memory used on system board |
36 64Kx1-bit DRAM chips in 4 banks of 9
chips |
Memory cache controller |
No |
Wait states: |
|
System board |
1 |
Adapter |
1 |
Standard Features |
|
ROM size |
40K |
ROM shadowing |
No |
Optional math coprocessor |
8087 |
Coprocessor speed |
4.77MHz |
Standard graphics |
CGA adapter with built-in 9-inch amber
CRT |
RS232C serial ports |
None standard |
UART chip used |
NS8250B |
Maximum speed (bits per second) |
9,600 bps |
Maximum number of ports supported |
2 |
Pointing device (mouse) ports |
None standard |
Parallel printer ports |
None standard |
Bi-directional |
No |
Maximum number of ports supported |
3 |
CMOS real-time clock (RTC) |
No |
CMOS RAM |
None |
Disk Storage |
|
Internal disk and tape drive bays |
2 half-height |
Number of 3 1/2-/5 1/4-inch bays |
0/2 |
Standard floppy drives |
1 or 2x360K |
Optional floppy drives: |
|
5 1/4-inch 360K |
Optional |
5 1/4-inch 1.2M |
No |
3 1/2-inch 720K |
Optional |
3 1/2-inch 1.44M |
No |
3 1/2-inch 2.88M |
No |
Hard disk controller included |
None |
Expansion Slots |
|
Total adapter slots |
8 |
Number of long/short slots |
2/6 |
Number of 8-/16-/32-bit slots |
8/0/0 |
Available slots (with video) |
6 |
Keyboard Specifications |
|
101-key Enhanced keyboard |
No |
Fast keyboard speed setting |
No |
Keyboard cable length |
6 feet |
Physical Specifications |
|
Footprint type |
Desktop |
Dimensions: |
|
Height |
8.0 inches |
Width |
20.0 inches |
Depth |
17.0 inches |
Weight |
31 pounds |
Environmental Specifications |
|
Power-supply output |
114 watts |
Worldwide (110/60,220/50) |
Yes |
Auto-sensing/switching |
No |
Maximum current: |
|
90-137 VAC |
4.0 amps |
Operating range: |
|
Temperature |
60-90° F |
Relative humidity |
8-80 percent |
Maximum operating altitude |
7,000 feet |
Heat (BTUs/hour) |
650 |
Noise (Average db, operating, 1m) |
42 |
FCC classification |
Class B |
Table 23.8 shows the part numbers for
the Portable PC.
Table 23.8 IBM Portable PC
Model Part Numbers
Description |
Number |
256K, one 360K half-height drive |
5155068 |
256K, two 360K half-height drives |
5155076 |
Half-height 360K floppy disk drive |
6450300 |
The disk drive used in the Portable PC
was a half-height drive, the same unit specified for use in
the PCjr. When the Portable PC was introduced, PCjr was the
only other IBM sold with the same half-height drive.
An Introduction
to the AT
IBM introduced the Personal Computer
AT (Advanced Technology) on August 14, 1984. The IBM AT
system included many features previously unavailable in IBM's
PC systems such as increased performance, an advanced 16-bit
microprocessor, high-density floppy disk and hard disk drives,
larger memory space, and an advanced coprocessor. Despite its
new design, the IBM AT incredibly retained compatibility with
most existing hardware and software products for the earlier
systems.
In most cases, IBM AT system
performance was from three to five times faster than the IBM
XT for single applications running DOS on both computers. The
performance increase is due to the combination of a reduced
cycle count for most instructions by the 80286 processor, an
increased system clock rate, 16-bit memory, and faster hard
disk and controller.
The AT system unit has been available
in several models: a floppy-disk-equipped base model (068) and
several hard-disk-enhanced models. Based on a
high-performance, 16-bit, Intel 80286 microprocessor, each
computer includes Cassette BASIC language in ROM and a CMOS
(Complementary Metal Oxide Semiconductor) clock and calendar
with battery backup. All models are equipped with a
high-density (1.2M) floppy disk drive, a keyboard, and a lock.
For standard memory, the base model offers 256K, and the
enhanced models offer 512K. In addition, the enhanced models
have a 20M or a 30M hard disk drive and a serial/parallel
adapter. Each system can be expanded through
customer-installable options. You can add memory (up to 512K)
for the base model by adding chips to the system board. You
can expand all models to 16M by installing memory
cards.
Besides the standard drives included
with the system, IBM only offered two different hard disks as
upgrades for the AT:
- 30M hard disk drive
- 20M hard disk drive
IBM also offered only three different
types of floppy drives for the AT:
- A second, high-density (1.2M) floppy
disk drive
- A double-density (320/360K) floppy
disk drive
- A new 3 1/2-inch 720K drive
The original 068 and 099 models of the
AT did not support the 720K drive in the BIOS; you had to add
a special driver (DRIVER.SYS--supplied with DOS) for the drive
to work properly. The later model ATs supported the 720K drive
directly in the BIOS, and also added support for the 1.44M
high-density 3 1/2-inch floppy drive, although IBM never sold
or officially supported such a drive in the AT.
You can install as many as two floppy
disk drives and one hard disk drive or one floppy disk drive
and two hard disk drives in the system unit. To use the
high-density 5 1/4-inch floppy disk drives properly, you must
have special floppy disks--5 1/4-inch, high-coercivity,
double-sided, soft-sectored disks. Due to track width problems
between the high-density (1.2M) drives and the double-density
(360K) drives, a double-density floppy disk drive (320/360K)
was available for compatibility with the standard PC or XT
systems. You can exchange disks reliably between the 1.2M and
the standard 360K drives if you use the proper method and
understand the recording process. For transferring data
between a system with a 1.2M drive to a system with a 360K
drive, you must start with a blank (never previously
formatted) 360K disk, which must be formatted and written only
by the 1.2M drive. No special precautions are needed to
transfer the data the other way. This information is covered
in Chapter 13, "Floppy Disk Drives." For complete interchange
reliability and to simplify the process however, IBM
recommends you purchase the 360K drive.
The AT motherboard has eight slots that
support cards for additional devices, features, or memory. Six
slots support the advanced 16-bit or 8-bit cards. Two slots
support only 8-bit cards. All system-unit models use one
16-bit slot for the fixed disk and floppy disk drive adapter.
The enhanced models use an additional 8-bit slot for the
serial/parallel adapter. The result is seven available
expansion slots for the base model and six available expansion
slots for enhanced models. Figure 23.9 shows the interior of
an AT system unit.
All AT models include a 192-watt
universal power supply; a temperature-controlled,
variable-speed cooling fan; and a security lock with key. The
user selects the power supply for a country's voltage range.
The cooling fan significantly reduces the noise in most
environments; the fan runs slower when the system unit is cool
and faster when the system unit is hot. When the system is
locked, no one can remove the system-unit cover, boot the
system, or enter commands or data from the keyboard, thereby
enhancing the system's security.
FIG.
23.9 The IBM AT unit
interior.
The keyboard is attached to the system
unit by a 9-foot coiled cable that enables the AT to adapt to
a variety of workspace configurations. The keyboard includes
key-location enhancements and mode indicators for improved
keyboard usability. Figure 23.10 shows the rear panel of an
AT.
FIG.
23.10 The IBM AT rear
panel.
Every system unit for the AT models has
these major functional components:
- Intel 80286 (6MHz or 8MHz)
microprocessor
- Socket for 80287 math
coprocessor
- Eight I/O expansion slots (six
16-bit, two 8-bit)
- 256K of dynamic RAM (base
model)
- 512K of dynamic RAM (enhanced
models)
- ROM-based diagnostics
(POST)
- BASIC language interpreter in
ROM
- Hard/floppy disk
controller
- 1.2M hard disk floppy
drive
- 20M or 30M hard disk drive (enhanced
models)
- Serial/parallel interface (enhanced
models)
- CMOS Clock-calendar and
configuration with battery backup
- Keylock
- 84-key keyboard or Enhanced, 101-key
keyboard (standard on newer models)
- Switchable worldwide power supply
AT Models and
Features
Since the introduction of the AT,
several models have become available. First, IBM announced two
systems: a base model (068) and an enhanced
model (099). The primary difference between the two
systems is the standard hard disk that came with the enhanced
model. IBM has introduced two other AT systems since the first
systems, each offering new features.
The first generation of AT systems has
a 6MHz system clock that dictates the processor cycle time.
The cycle time, the system's smallest interval of time,
represents the speed at which operations occur. Every
operation in a computer takes at least one or (usually)
several cycles to complete. Therefore, if two computers are
the same in every way except for the clock speed, the system
with the faster clock rate executes the same operations in a
shorter time proportional to the difference in clock speed.
Cycle time and clock speed are two different ways of
describing the same thing. Discussions of clock speed are
significant when you consider buying the AT because not all
models have the same clock speed.
All models of the AT included a
combination hard/floppy disk controller that was really two
separate controllers on the same circuit board. The board was
designed by IBM and Western Digital (WD), and manufactured for
IBM by WD. This controller had no on-board ROM BIOS like the
Xebec hard disk controller used in the XT. In the AT, IBM
built full support for the hard disk controller directly into
the motherboard ROM BIOS. To support different types of hard
disks, IBM encoded a table into the motherboard ROM that
listed the parameters of various drives that could be
installed. In the first version of the AT, with a ROM BIOS
dated 01/10/84, only the first 14 types in the table were
filled in. Type 15 itself was reserved for internal reasons,
and was not usable. Other table entries from 16 through 47
were left unused and were actually filled with zeros. Later
versions of the AT added new drive types to the tables,
starting from Type 16 and up.
The first two AT models were the 068
(base) model, which had 256K on the motherboard and a single
1.2M floppy disk drive; and the model 099 (enhanced), which
had a 20M hard disk drive, a serial/parallel adapter, and 512K
on the motherboard. IBM designated the motherboard on these
computers as Type 1, which is larger than the later Type 2
board and used an unusual memory layout. The memory is
configured as four banks of 128K chips--a total of 512K on the
board. This configuration sounds reasonable until you realize
that a 128K chip does not really exist in the physical form
factor that IBM used. IBM actually created this type of memory
device by stacking one 64K chip on top of another 64K chip and
soldering the two together. My guess is that IBM had many 64K
chips to use, and the AT was available to take
them.
On October 2, 1985, IBM announced a new
model of the AT, the Personal Computer AT Model 239. The
system has all the standard features of the AT Model 099, but
also has a 30M hard disk rather than a 20M hard disk. A
second, optional 30M hard disk drive expands the Model 239's
hard disk storage to 60M. This unit's motherboard, a
second-generation design IBM calls Type 2, is about 25 percent
smaller than the Type 1 but uses the same mounting locations
for physical compatibility. All important items, such as the
slots and connectors, remain in the same locations. Other
major improvements in this board are in the memory. The 128K
memory chips were replaced by 256K devices. Now only two banks
of chips were needed to get the same 512K on the
board.
The AT Model 239 includes these items:
- 512K of RAM
(standard)
- 6MHz Type 2 motherboard with 256K
memory chips
- Serial/parallel adapter
(standard)
- 30M hard disk
(standard)
- New ROM BIOS (dated 06/10/85). ROM
supports 3 1/2-inch 720K floppy drives without using
external driver programs, and 22 usable hard disk types (up
to Type 23), including the supplied 30M disk. POST "fixes"
clock rate to 6MHz.
The Type 2 motherboard's design is a
big improvement on Type 1's; the Type 2 mother- board improved
internal-circuit timing and layout. Improvements in the
motherboard indicated that the system would be pushed to
higher speeds--exactly what happened with the next round of
introductions.
In addition to obvious physical
differences, the Model 239 includes significantly different
ROM software from the previous models. The new ROM supports
more types of hard and floppy disks, and its new POST prevents
alteration of the clock rate from the standard 6MHz models.
Because support for the 30M hard disk is built into the new
ROM, IBM sold a 30M hard disk upgrade kit that included the
new ROM for the original AT systems. This $1,795 kit
represented the only legal way to obtain the newer
ROM.
The 30M hard disk drive upgrade kit for
the Personal Computer AT Models 068 and 099 included all the
features in the 30M hard disk drive announced for the AT Model
239. The upgrade kit also had a new basic input-output
subsystem (BIOS), essential to AT operation. The new ROM BIOS
supports 22 drive types (compared to the original 14 in
earlier ATs), including the new 30M drive. To support the 30M
hard disk drive, a new diagnostics floppy disk and an updated
guide-to-operations manual are shipped with this
kit.
The 30M update kit includes these
items:
- 30M hard disk drive
- Two new ROM BIOS
modules
- Channel keeper bar (a bracket for
the fixed disk)
- Data cable for the hard
disk
- Diagnostics and Setup
disk
- An insert to the AT
guide-to-operations manual
Some people were upset initially that
IBM had "fixed" the microprocessor clock to 6MHz in the new
model, thereby disallowing any possible "hot rod" or
overclocking modifications. Many people realized that the
clock crystal on the AT models was socketed so that the
crystal could be replaced easily by a faster one. More
importantly, because the AT circuit design is modular,
changing the clock crystal does not have repercussions
throughout the rest of the system, as is the case in the PC
and PC XT. For the price of a new crystal (from $1 to $30) and
the time needed to plug it in, someone easily could increase
an AT's speed by 30 percent, and sometimes more.
Unfortunately, due to the POST in the newer model's BIOS, you
no longer can implement a simple speedup alteration without
also changing the ROM BIOS as well.
Many people believed that this change
was made to prevent the AT from being "too fast" and therefore
competing with IBM's minicomputers. In reality, the earlier
motherboard was run intentionally at 6MHz because IBM did not
believe that the ROM BIOS software and critical system timing
was fully operational at a higher speed. Also, IBM used some
components that were rated only for 6MHz operation, starting
of course with the CPU. Users who increased the speed of their
early computers often received DOS error messages from timing
problems, and in some cases, total system lockups due to
components not functioning properly at the higher
speeds.
Many companies selling speedup kits
sold software to help smooth over some of these problems, but
IBM's official solution was to improve the ROM BIOS software
and motherboard circuitry, and to introduce a complete new
system running at the faster speed. If you want increased
speed no matter what model you have, several companies used to
sell clock-crystal replacements that were frequency
synthesizers rather than a fixed type of crystal. The units
can wait until the POST is finished and change midstream to an
increased operating speed. Unfortunately, I don't know of
anyone who is still making or selling these
upgrades.
If you really want to speed up your AT
by installing a faster clock crystal, instructions on how to
burn your own set of BIOS without the check can be found on
the CD accompanying this book. However, it requires the use of
a specialized PROM or EPROM burner, or access to
one.
On April 2, 1986, IBM introduced the
Personal Computer AT Models 319 and 339. These were the last
and best AT models, and were an enhancement of the earlier
Model 239. The primary difference from the Model 239 is a
faster clock crystal that provides 8MHz operation. The Model
339 has a new keyboard--the Enhanced keyboard--with 101 keys
rather than the usual 84. Model 319 is the same as Model 339,
but includes the original keyboard.
Highlights of the Models 319 and 339
are shown in this list:
- Faster processor speed
(8MHz)
- Type 2 motherboard, with 256K
chips
- 512K of RAM
(standard)
- Serial/parallel adapter
(standard)
- 30M hard disk
(standard)
- New ROM BIOS (dated 11/15/85). ROM
support for 22 usable types (up to type 23) of hard disks,
and 3 1/2-inch drives, at both 720K and 1.44M capacities.
POST "fixes" clock rate to 8MHz.
- 101-key Enhanced keyboard (standard
on Model 339)
The most significant physical
difference in these new systems is the Enhanced keyboard on
the Model 339. The keyboard, similar to a 3270 keyboard, has
101 keys. It could be called the IBM "corporate" keyboard
because it is standard on all new desktop systems. The 84-key
PC keyboard still was available, with a new 8MHz model, as the
Model 319.
These new 8MHz systems were available
only in an enhanced configuration with a standard 30M hard
drive. If you wanted a hard disk larger than IBM's 30M, you
could either add a second drive or simply replace the 30M unit
with something larger.
ROM support for 3 1/2-inch disk drives
at both 720K and 1.44M exists only in Models 339 and 319. In
particular, the 1.44M drive, although definitely supported by
the ROM BIOS and controller, was never offered as an option by
IBM. This means that the IBM Setup program found on the
Diagnostics and Setup disk did not offer the 1.44M floppy
drive as a choice when configuring the system! Anybody adding
such a drive had to use one of the many Setup replacement
programs available in the public domain, or "borrow" one from
an IBM-compatible system that used a floppy disk-based setup
program. Adding the 1.44M drive became one of the most popular
upgrades for the AT systems because many newer systems came
with that type of drive as standard equipment. Earlier AT
systems still can use the 720K and 1.44M drives, but they need
to either upgrade the ROM to support it (recommended) or
possibly use software drivers to make them work.
AT BIOS
Versions
There have been three different BIOS
versions used in the IBM AT. They can be identified by their
date and summarized as follows:
- January 1, 1984: The first AT BIOS
version supported only 1.2M and 360K floppy drives directly.
Only 14 hard disk types were supported. It came on the Model
068 and 099 systems with the Type 1
motherboard.
- June 10, 1985: The second AT BIOS
added support for 720K 3 1/2-inch drives directly (no
drivers required). Also more hard disk drive types were
added, for a total of 22 usable types. A new test was added
to the POST which causes the POST to fail if the clock speed
is altered from 6MHz. This BIOS was used on the Model 239
with a Type 2 motherboard.
- November 15, 1985: The third and
final AT BIOS added support for a 1.44M 3 1/2-inch drives
(no drivers required). Enhanced 101-key keyboard support was
added. The POST test checks for 8MHz operation, and fails if
the system is running at any other speed. This BIOS was used
on Model 319 and 339 systems, and came on a Type 2
motherboard.
Table 23.1 Lists the different IBM
Family/1 (PC, XT, and AT) BIOS versions. It also shows the ID,
Submodel, and Revision bytes which can be determined by the
software function call Int 15h, C0 = Return System Configuration Parameters
Some of the systems such as the PC and
earlier XT and AT systems only support the ID byte; the
submodel and revision bytes had not been established when
those systems were developed. The table also shows the number
of drive types supported in the AT and XT-286 systems
BIOS.
The BIOS date is stored in all
PC-compatible systems at memory address FFFF5h. To display the
date of your BIOS, a simple DEBUG command can be used
to view this address. DEBUG is a command program
supplied with MS-DOS. At the DOS prompt, execute the following
commands to run DEBUG, display the date stored in
your BIOS, and then exit back to DOS: C:\>DEBUG
-D FFFF:5 L 8
FFFF:0000 30 31 2F-32 32 2F 39 37 01/22/97
-Q
In this example, the system queried
shows a BIOS date of 01/22/97.
AT Motherboard BIOS Hard Drive
Tables
The AT BIOS contains a special table
that is used by the hard disk controller driver to determine
the hard drive parameters. When a hard disk is installed into
this type of system, the "type" of drive is entered into the
CMOS RAM by whoever has installed the drive. Then every time
the system boots, it looks up the parameters by consulting the
CMOS RAM for the particular type selected. Older systems were,
therefore, limited to what different drives they could support
or recognize by the entries burned into their BIOS table. The
table used in IBM AT and PS/2 systems is shown here in this
section.
The various IBM AT and PS/2 systems
that use a BIOS drive table do not necessarily have all of the
entries shown here. The number of table entries contained in a
particular system BIOS can vary from one version to the next.
For example, the original AT BIOS (01/10/84) only had Types
1-14 usable, while the later AT BIOS versions (06/10/85 and
11/15/85) had 1-14 and 16-23 usable. The XT-286 had 1-14 and
16-24 as usable types. Some of the PS/1 and PS/2 systems had
the table filled as far as Type 44.
Non-IBM systems quickly adopted special
"User Definable" or even "Auto-Detect" types where you could
either manually enter the complete table entry (rather than
selecting a predetermined "type"), or the system would
automatically read the type information directly from the
drive.
NOTE: If you have a non-IBM
PC-compatible system, the IBM table may be inaccurate for
many of the entries past Type 15. Instead, you should
consult your CMOS Setup program; most will show the
available types as you scroll through them. Another option
is to consult your system, motherboard, or BIOS
documentation to see if it shows what the correct table
entries are. A final alternative is a program such as the
Seagate FINDTYPE program which will scan your BIOS, locate
the table, and display or print it for viewing. This program
can be downloaded from the Seagate Web site or BBS. Most
compatibles follow the IBM table for at least the first 15
entries.
Most PS/2 systems have the drive's
defect map written as data on the drive one cylinder beyond
the highest reported cylinder. This special data is read by
the IBM PS/2 Advanced Diagnostics low-level format program.
This process automates the entry of the defect list and
eliminates the chance of human error, as long as you use only
the IBM PS/2 Advanced Diagnostics for hard disk low-level
formatting on those systems.
This type of table does not apply to
IBM Enhanced Small Device Interface (ESDI) or SCSI hard disk
controllers, host adapters, and drives. Because the ESDI and
SCSI controllers or host adapters query the drive directly for
the required parameters, no table-entry selection is
necessary. Note, however, that the table for the ST-506/412
drives can still be found currently in the ROM BIOS of most of
the PS/2 systems, even if the model came standard with an ESDI
or SCSI disk subsystem.
Table 23.9 shows the IBM motherboard
ROM BIOS hard disk parameters for AT or PS/2 systems using
ST-506/412 (standard or IDE) controllers.
Table 23.9 IBM AT and PS/2
BIOS Hard Disk Table
Type |
Cylinders |
Heads |
WPC |
Ctrl |
LZ |
S/T |
Meg |
M |
1 |
306 |
4 |
128 |
00h |
305 |
17 |
10.16 |
10.65 |
2 |
615 |
4 |
300 |
00h |
615 |
17 |
20.42 |
21.41 |
3 |
615 |
6 |
300 |
00h |
615 |
17 |
30.63 |
32.12 |
4 |
940 |
8 |
512 |
00h |
940 |
17 |
62.42 |
65.45 |
5 |
940 |
6 |
512 |
00h |
940 |
17 |
46.82 |
49.09 |
6 |
615 |
4 |
65535 |
00h |
615 |
17 |
20.42 |
21.41 |
7 |
462 |
8 |
256 |
00h |
511 |
17 |
30.68 |
32.17 |
8 |
733 |
5 |
65535 |
00h |
733 |
17 |
30.42 |
31.90 |
9 |
900 |
15 |
65535 |
08h |
901 |
17 |
112.06 |
117.50 |
10 |
820 |
3 |
65535 |
00h |
820 |
17 |
20.42 |
21.41 |
11 |
855 |
5 |
65535 |
00h |
855 |
17 |
35.49 |
37.21 |
12 |
855 |
7 |
65535 |
00h |
855 |
17 |
49.68 |
52.09 |
13 |
306 |
8 |
128 |
00h |
319 |
17 |
20.32 |
21.31 |
14 |
733 |
7 |
65535 |
00h |
733 |
17 |
42.59 |
44.66 |
15* |
0 |
0 |
0 |
00h |
0 |
0 |
0.00 |
0.00 |
16 |
612 |
4 |
0 |
00h |
663 |
17 |
20.32 |
21.31 |
17 |
977 |
5 |
300 |
00h |
977 |
17 |
40.55 |
42.52 |
18 |
977 |
7 |
65535 |
00h |
977 |
17 |
56.77 |
59.53 |
19 |
1024 |
7 |
512 |
00h |
1023 |
17 |
59.50 |
62.39 |
20 |
733 |
5 |
300 |
00h |
732 |
17 |
30.42 |
31.90 |
21 |
733 |
7 |
300 |
00h |
732 |
17 |
42.59 |
44.66 |
22 |
733 |
5 |
300 |
00h |
733 |
17 |
30.42 |
31.90 |
23 |
306 |
4 |
0 |
00h |
336 |
17 |
10.16 |
10.65 |
24 |
612 |
4 |
305 |
00h |
663 |
17 |
20.32 |
21.31 |
25 |
306 |
4 |
65535 |
00h |
340 |
17 |
10.16 |
10.65 |
26 |
612 |
4 |
65535 |
00h |
670 |
17 |
20.32 |
21.31 |
27 |
698 |
7 |
300 |
20h |
732 |
17 |
40.56 |
42.53 |
28 |
976 |
5 |
488 |
20h |
977 |
17 |
40.51 |
42.48 |
29 |
306 |
4 |
0 |
00h |
340 |
17 |
10.16 |
10.65 |
30 |
611 |
4 |
306 |
20h |
663 |
17 |
20.29 |
21.27 |
31 |
732 |
7 |
300 |
20h |
732 |
17 |
42.53 |
44.60 |
32 |
1023 |
5 |
65535 |
20h |
1023 |
17 |
42.46 |
44.52 |
33 |
614 |
4 |
65535 |
20h |
663 |
25 |
29.98 |
31.44 |
34 |
775 |
2 |
65535 |
20h |
900 |
27 |
20.43 |
21.43 |
35 |
921 |
2 |
65535 |
20h |
1000 |
33 |
29.68 |
31.12 |
36 |
402 |
4 |
65535 |
20h |
460 |
26 |
20.41 |
21.41 |
37 |
580 |
6 |
65535 |
20h |
640 |
26 |
44.18 |
46.33 |
38 |
845 |
2 |
65535 |
20h |
1023 |
36 |
29.71 |
31.15 |
39 |
769 |
3 |
65535 |
20h |
1023 |
36 |
40.55 |
42.52 |
40 |
531 |
4 |
65535 |
20h |
532 |
39 |
40.45 |
42.41 |
41 |
577 |
2 |
65535 |
20h |
1023 |
36 |
20.29 |
21.27 |
42 |
654 |
2 |
65535 |
20h |
674 |
32 |
20.44 |
21.43 |
43 |
923 |
5 |
65535 |
20h |
1023 |
36 |
81.12 |
85.06 |
44 |
531 |
8 |
65535 |
20h |
532 |
39 |
80.89 |
84.82 |
45 |
0 |
0 |
0 |
00h |
0 |
0 |
0.00 |
0.00 |
46 |
0 |
0 |
0 |
00h |
0 |
0 |
0.00 |
0.00 |
47 |
0 |
0 |
0 |
00h |
0 |
0 |
0.00 |
0.00 | *Table entry 15 is reserved to act as a
pointer to indicate that the type is greater than 15. Type
= Table entry number Cylinders = Total number of
cylinders Heads = Total number of heads WPC = Write
Pre-Compensation starting cylinder 65535 = No Write
Pre-Compensation (also shown as -1) 0 = Write
Pre-Compensation on all cylinders Ctrl = Control byte, with
values according to the following table:
Bit Number |
Hex |
Meaning |
Bit 0 |
01h |
Not used (XT = drive step rate) |
Bit 1 |
02h |
Not used (XT = drive step rate) |
Bit 2 |
04h |
Not used (XT = drive step rate) |
Bit 3 |
08h |
More than eight heads |
Bit 4 |
10h |
Not used (XT = imbedded servo
drive) |
Bit 5 |
20h |
OEM defect map at (cylinders + 1) |
Bit 6 |
40h |
Disable ECC retries |
Bit 7 |
80h |
Disable disk access
retries | LZ =
Landing-Zone cylinder used head parking S/T = Number of
Sectors per Track Meg = Drive capacity in Megabytes M =
Drive capacity in Millions of bytes
Modifying ROM BIOS Hard Disk Drive
Parameter Tables
Because the IBM tables in the AT and
XT-286 systems (as well as many of the compatibles of that
day) were fixed, technicians often found it necessary to
modify the BIOS in those systems to add drive types for new
drives I wanted to install. For example, I added two new drive
types to one of my old AT systems. Those types--25 and
26--have these parameters:
Type |
Cylinders |
Heads |
WPC |
Ctrl |
LZ |
S/T |
Meg |
M |
25 |
918 |
15 |
65535 |
08h |
918 |
17 |
114.30 |
119.85 |
26 |
918 |
15 |
65535 |
08h |
918 |
26 |
174.81 |
183.31 | WPC = Write Pre-Compensation start cylinder
Ctrl = Control Byte, 08h = More than 8 heads, else 00h
LZ = Landing Zone or head parking cylinder S/T =
Sectors per Track Meg = Megabytes M = Millions of
bytes
In my old AT system, these table
entries originally were unused (zeros), as are the remainder
of types from 27-47. By burning a new set of ROMs with these
two new completed entries, I was able to use a Maxtor XT-1140
drive to maximum capacity with an MFM 17-sector per track
controller (as Type 25) or an RLL 26-sector per track
controller (as Type 26). This method precluded the need for a
controller with its own separate on-board BIOS to override the
motherboard table values and therefore also saved memory in
the C000 or D000 UMA segments, where such a hard disk
controller ROM normally would reside.
TIP: If you are interested in
performing this modification, get the IBM AT Technical
Reference Manual (sold by IBM or Annabooks), which documents
the position and format of the drive tables in the BIOS.
Changing the Hard Disk Controller
Head Step Rate
Another more complicated modification
that you can perform to the AT BIOS is to increase the
stepping rate of the hard disk controller. The first edition
of this book briefly mentioned this modification, and a reader
wrote to me to express interest in it. Details of the
modification can be found on the CD; however, the performance
is relatively slight.
AT Technical
Specifications
Technical information for the AT system
is described in this section. You will find information about
the system architecture, memory configurations and capacities,
standard system features, disk storage, expansion slots, and
keyboard specifications, as well as physical and environmental
specifications. This type of information can be useful in
determining what types of parts are needed when you are
upgrading or repairing these systems. Figures 23.11 and 23.12
show the layout and components on the two different AT
motherboards.
FIG.
23.11 The IBM AT Type 1
motherboard.
System Architecture |
|
Microprocessor |
80286 |
Clock speed |
6 or 8MHz |
Bus type |
ISA (Industry Standard
Architecture) |
Bus width |
16-bit |
Interrupt levels |
16 (11 usable) |
Type |
Edge-triggered |
Shareable |
No |
DMA channels |
8 (7 usable) |
Bus masters supported |
Yes |
Upgradable processor complex |
No |
FIG.
23.12 The IBM AT Type 2
motherboard.
Memory |
|
|
Standard on system board |
512K |
|
Maximum on system board |
512K |
|
Maximum total memory |
16M |
|
Memory speed (ns) and type |
150ns dynamic RAM chips |
|
System board memory-socket type |
16-pin DIP |
|
Number of memory-module sockets |
18 or 36 (2 or 4 banks of 18) |
|
Memory used on system board |
36 128Kx1-bit DRAM chips in 2 banks of
18, or 18 256Kx1-bit chips in one bank |
|
Memory cache controller |
No |
|
Wait states: |
|
|
System board |
1 |
|
Adapter |
1 |
|
Standard Features |
|
|
ROM size |
64K |
|
ROM shadowing |
No |
|
Optional math coprocessor |
80287 |
|
Coprocessor speed |
4 or 5.33MHz |
|
Standard graphics |
None standard |
|
RS232C serial ports |
1 (some models) |
|
UART chip used |
NS16450 |
|
Maximum speed (bits per second) |
9,600 bps |
|
Maximum number of ports supported |
2 |
|
Pointing device (mouse) ports |
None standard |
|
Parallel printer ports |
1 (some models) |
|
Bi-directional |
Yes |
|
Maximum number of ports supported |
3 |
|
CMOS real-time clock (RTC) |
Yes |
|
CMOS RAM |
64 bytes |
|
Battery life |
5 years |
|
Disk Storage |
|
|
Internal disk and tape drive bays |
1 full-height and 2 half-height |
|
Number of 3 1/2-, 5 1/4-inch bays |
0/3 |
|
Standard floppy drives |
1x1.2M |
|
Optional floppy drives: |
|
|
5 1/4-inch 360K |
Optional |
|
5 1/4-inch 1.2M |
Standard |
|
3 1/2-inch 720K |
Optional |
|
3 1/2-inch 1.44M |
Optional (8MHz models3 1/2-inch 2.88M |
No |
Hard disk controller included: |
ST-506/412 (Western Digital WD1002-WA2 or
WD1003 WA2) |
|
ST-506/412 hard disks available |
20/30M |
|
Drive form factor |
5 1/4-inch |
|
Drive interface |
ST-506/412 |
|
Drive capacity: |
20M |
30M |
Average access rate (ms) |
40 |
40 |
Encoding scheme |
MFM |
MFM |
BIOS drive type number |
2 |
20 |
Cylinders |
615 |
733 |
Heads |
4 |
5 |
Sectors per track |
17 |
17 |
Rotational speed (RPMs) |
3600 |
3600 |
Disk storage |
|
|
Interleave factor |
3:1 |
3:1 |
Data transfer rate (K/sec) |
170 |
170 |
Automatic head parking |
Yes |
Yes |
Expansion Slots |
|
|
Total adapter slots |
8 |
|
Number of long and short slots |
8/0 |
|
Number of 8-/16-/32-bit slots |
2/6/0 |
|
Available slots (with video) |
5 |
|
Keyboard Specifications |
|
|
101-key Enhanced keyboard |
Yes (8MHz models) |
|
Fast keyboard speed setting |
Yes |
|
Keyboard cable length |
6 feet |
|
Physical Specifications |
|
|
Footprint type |
Desktop |
|
Dimensions: |
|
|
Height |
6.4 inches |
|
Width |
21.3 inches |
|
Depth |
17.3 inches |
|
Weight |
43 pounds |
|
Environmental Specifications |
|
|
Power-supply output |
192 watts |
|
Worldwide (110/60,220/50) |
Yes |
|
Auto-sensing/switching |
No |
|
Maximum current: |
|
|
90-137 VAC |
5.0 amps |
|
Operating range: |
|
|
Temperature |
60-90° F |
|
Relative humidity |
8-80 percent |
|
Maximum operating altitude |
7,000 feet |
|
Heat (BTUs/hour) |
1229 |
|
Noise (Average db, operating, 1m) |
42 |
|
FCC classification |
Class B |
|
Table 23.10 shows the AT system-unit
part-number information.
Table 23.10 IBM AT Model
Part Numbers
Description |
Number |
AT 6MHz/84-key keyboard, 256K |
|
one 1.2M floppy drive |
5170068 |
AT 6MHz/84-key keyboard, 512K,
serial/parallel |
|
one 1.2M floppy drive, 20M hard disk |
5170099 |
one 1.2M floppy drive, 30M hard disk |
5170239 |
AT 8MHz/84-key keyboard, 512K,
serial/parallel |
|
one 1.2M floppy drive, 30M hard disk |
5170319 |
AT 8MHz/101-keyboard, 512K,
serial/parallel |
|
one 1.2M floppy drive, 30M hard disk |
5170339 |
System Options |
|
20M fixed disk drive |
6450205 |
30M fixed disk drive |
6450210 |
30M fixed disk drive upgrade kit |
6450468 |
360K half-height floppy disk drive
(AT) |
6450207 |
1.2M high-density drive |
6450206 |
3 1/2-inch, half-height, 720K external
drive (AT) |
2683191 |
Serial/parallel adapter |
6450215 |
80287 math coprocessor option |
6450211 |
Floor-standing enclosure |
6450218 |
Enhanced Keyboard Accessories |
|
Clear keycaps (60) with paper inserts |
6341707 |
Blank light keycaps |
1351710 |
Blank dark keycaps |
1351728 |
Paper keycap inserts (300) |
6341704 |
Keycap-removal tools (6) |
1351717 |
An Introduction
to the XT Model 286
On September 9, 1986, IBM introduced a
new AT-type system disguised inside the chassis and case of an
XT. This XT Model 286 system featured increased memory, an
Intel 80286 microprocessor, and as many as three internal
drives standard. The computer combined an XT's
cost-effectiveness, flexibility, and appearance with the
high-speed, high- performance technology of the Intel 80286
microprocessor. This model looked like an XT, but underneath
the cover, it was all AT.
The IBM XT Model 286 can operate as
much as three times faster than earlier models of the XT in
most applications. It has a standard 640K of memory. Various
memory-expansion options enable users to increase its memory
to 16M.
Standard features in this system
include a half-height, 1.2M, 5 1/4-inch, high-density floppy
disk drive; a 20M hard disk drive; a serial/parallel adapter
card; and the IBM Enhanced keyboard. You can select an
optional, internal, second floppy disk drive from the
following list:
- Half-height, 3 1/2-inch, 720K floppy
drive
- Half-height, 3 1/2-inch, 1.44M
floppy drive
- Half-height, 5 1/4-inch, 1.2M floppy
drive
- Half-height, 5 1/4-inch, 360K floppy
drive
The IBM XT Model 286's performance
stems primarily from the AT motherboard design, with 16-bit
I/O slots and an Intel 80286 processor running at 6MHz. In
addition to the type of processor used, clock speed and memory
architecture are the primary factors in determining system
performance. Depending on the model, the IBM AT's clock speed
is 6 or 8MHz, with one wait state; and the XT Model 286
processes data at 6MHz, with zero wait states. The elimination
of a wait state improves performance by increasing processing
speed for system memory access. The zero-wait-state design
makes the XT Model 286 definitely faster than the original AT
models that ran at 6MHz and about equal in speed to the 8MHz
AT systems. Based on tests, the XT Model 286 also is about
three times faster than an actual XT.
Because the XT Model 286 is an AT-class
system, the processor supports both real and protected modes.
Operating in real address mode, the 80286 is 8088-compatible;
therefore, you can use most software that runs on the standard
PC systems. In real address mode, the system can address as
much as 1M of RAM. Protected mode provides a number of
advanced features to facilitate multitasking operations.
Protected mode provides separation and protection of programs
and data in multitasking environments. In protected mode, the
80286 can address as much as 16M of real memory and 1G of
virtual memory. In this mode, the XT Model 286 can run
advanced operating systems such as OS/2 and UNIX. When the XT
Model 286 was introduced, it was the least-expensive IBM
system capable of running a true multitasking operating
system.
The IBM XT Model 286 has a standard
640K of RAM. Memory options enable the system to grow to 15
1/2M, much higher than the 640K limit in other PC XTs. If you
add an operating system such as OS/2 or Windows, you can take
advantage of the larger memory capacities that the XT Model
286 provides.
A 20M hard disk drive is a standard
feature in the XT Model 286, as is a 5 1/4-inch, 1.2M,
high-density floppy disk drive. A similar floppy disk drive is
standard on all models of the AT. Floppy disks formatted on a
1.2M floppy disk drive therefore can be read by an AT or an XT
Model 286. The 1.2M floppy disk drive also can read floppy
disks formatted with PC-family members that use a 360K floppy
disk drive. Figure 23.13 shows the interior of an XT 286
system unit.
The XT Model 286 features the IBM
Enhanced keyboard with indicator lights. Many IBM personal
computers use the Enhanced keyboard, but the XT Model 286 was
the first PC XT to feature keyboard indicator
lights.
Five slots support the advanced 16-bit
cards or 8-bit cards; three support only 8-bit cards. Two of
the three 8-bit slots support only short cards.
A hard disk and floppy drive adapter
card are standard features in the XT Model 286. This
multifunction card takes only one 16-bit slot and supports as
many as four disk drives (two floppy disk drives and two hard
disk drives).
The serial/parallel adapter, another
standard feature, is a combination card that requires only one
slot (either type) and provides a serial and a parallel port.
The parallel portion of the adapter has the capacity to attach
devices, such as a parallel printer, that accept 8 bits of
parallel data. The fully programmable serial portion supports
asynchronous communications from 50 bps to 9,600 bps, although
even higher speeds are possible with the right software. The
serial portion requires an optional serial-adapter cable or a
serial-adapter connector. When one of these options is
connected to the adapter, all the signals in a standard EIA
RS-232C interface are available. You can use the serial port
for interfacing a modem, a remote display terminal, a mouse,
or other serial device. The XT Model 286 supports as many as
two serial/parallel adapters.
FIG.
23.13 The IBM XT-286
interior.
A standard IBM XT Model 286 offers
these features:
- 80286 processor at 6 MHz with 0 wait
states
- 640K of motherboard
memory
- 1.2M floppy drive
- 20M hard disk
- Five 16-bit and three 8-bit
expansion slots
- Fixed disk/floppy disk drive adapter
(occupies one 16-bit expansion slot)
- Serial/parallel adapter (occupies
one 16-bit expansion slot)
- Enhanced 101-key Keyboard with
indicator lights
- CMOS Time-and-date clock with
battery backup
XT Model 286
Models and Features
The XT Model 286 processor is as much
as three times faster internally than the preceding XT family
and as much as 25 percent faster than the AT Model 239,
depending on specific applications. A 20M fixed disk and a
1.2M, 5 1/4-inch floppy disk drive were standard on the XT
Model 286. One additional floppy disk drive can be installed
internally as drive B. Any type of floppy drive can be added
as a second half-height floppy drive, including both the
double and high-density versions of the 5 1/4- and 3 1/2-inch
drives.
If you want to be able to read standard
5 1/4-inch data or program floppy disks created by the XT
Model 286 on other PC systems, you might want to add a 5
1/4-inch 360K floppy disk drive, which provides full
read/write compatibility with those systems. This is due to
the fact that the 1.2M drives write a narrower track than the
360K drives, and are unable to properly overwrite a floppy
disk written on first by a 360K drive. If full read/write
compatibility with 360K drives is not important, you can add a
second 1.2M high-density floppy disk drive.
You can add any 3 1/2-inch drive,
including the 720K and 1.44M versions. Because the 1.44M does
not have any read/write compatibility problems with the 720K
drives, however, and the 1.44M drives always can operate in
720K mode, I suggest adding only the 1.44M 3 1/2-inch drives
rather than the 720K versions. The higher-density drive is
only a small extra expense compared to the double-density
version. Most people do not know that full ROM BIOS support
for these 1.44M drives is provided in the XT Model 286.
Unfortunately, because IBM never offered the 1.44M drive as an
option, the supplied Setup program does not offer the 1.44M
drive as a choice in the Setup routine. Instead, you have to
use one of the many available public domain AT type setup
programs, or "borrow" such a program from an AT-compatible
system.
XT Model 286
Technical Specifications
The technical information for the XT
286 system described in this section covers the system
architecture, memory configurations and capacities, standard
system features, disk storage, expansion slots, keyboard
specifications, and also physical and environmental
specifications. You can use this information to determine the
parts you need when you are upgrading or repairing these
systems. Figure 23.14 shows the layout and components on the
XT 286 motherboard.
System Architecture
Microprocessor |
80286 |
Clock speed |
6MHz |
Bus type |
ISA (Industry Standard
Architecture) |
Bus width |
16-bit |
Interrupt levels |
16 (11 usable) |
Type |
Edge-triggered |
Shareable |
No |
DMA channels |
8 (7 usable) |
Bus masters supported |
Yes |
Upgradable processor complex |
No |
Memory |
|
Standard on system board |
640K |
Maximum on system board |
640K |
Maximum total memory |
16M |
Memory speed (ns) and type |
150ns dynamic RAM chips/SIMMs |
System board memory-socket type |
30-pin (9-bit) SIMM |
Number of memory-module sockets |
2 |
Memory used on system board |
One bank of 4 64Kx4-bit and 2 64Kx1-bit
DRAM parity chips, and one bank of 2 9-bit SIMMs |
Memory cache controller |
No |
Wait states: |
|
System board |
0 |
Adapter |
1 |
FIG.
23.14 The IBM XT-286
motherboard.
Standard Features |
|
ROM size |
64K |
ROM shadowing |
No |
Optional math coprocessor |
80287 |
Coprocessor speed |
4.77MHz |
Standard graphics |
None standard |
RS232C serial ports |
1 |
UART chip used |
NS16450 |
Maximum speed (bits per second) |
9,600 bps |
Maximum number of ports supported |
2 |
Pointing device (mouse) ports |
None standard |
Parallel printer ports |
1 |
Bi-directional |
Yes |
Maximum number of ports supported |
3 |
CMOS real-time clock (RTC) |
Yes |
CMOS RAM |
64 bytes |
Battery life |
5 years |
Disk Storage |
|
Internal disk and tape drive bays |
1 full-height and 2 half-height |
Number of 3 1/2-/5 1/4-inch bays |
0/3 |
Standard floppy drives |
1x1.2M |
Optional floppy drives: |
|
5 1/4-inch 360K |
Optional |
5 1/4-inch 1.2M |
Standard |
3 1/2-inch 720K |
Optional |
3 1/2-inch 1.44M |
Optional |
3 1/2-inch 2.88M |
No |
Hard disk controller included: |
ST-506/412 (Western Digital
WD1003-WA2) |
ST-506/412 hard disks available |
20M |
Drive form factor |
5 1/4-inch |
Drive interface |
ST-506/412 |
Drive capacity |
20M |
Average access rate (ms) |
65 |
Encoding scheme |
MFM |
BIOS drive type number |
2 |
Cylinders |
615 |
Heads |
4 |
Sectors per track |
17 |
Rotational speed (RPMs) |
3600 |
Interleave factor |
3:1 |
Data transfer rate (K/sec) |
170 |
Automatic head parking |
No |
Expansion Slots |
|
Total adapter slots |
8 |
Number of long and short slots |
6/2 |
Number of 8-/16-/32-bit slots |
3/5/0 |
Available slots (with video) |
5 |
Keyboard Specifications |
|
101-key Enhanced keyboard |
Yes |
Fast keyboard speed setting |
Yes |
Keyboard cable length |
6 feet |
Physical Specifications |
|
Footprint type |
Desktop |
Dimensions: |
|
Height |
5.5 inches |
Width |
19.5 inches |
Depth |
16.0 inches |
Weight |
28 pounds |
Environmental Specifications |
|
Power-supply output |
157 watts |
Worldwide (110v/60Hz, 220v/50Hz) |
Yes |
Auto-sensing/switching |
Yes |
Maximum current: |
|
90-137 VAC |
4.5 amps |
Operating range: |
|
Temperature |
60-90° F |
Relative humidity |
8-80 percent |
Maximum operating altitude |
7,000 feet |
Heat (BTUs/hour) |
824 |
Noise (Average db, operating, 1m) |
42 |
FCC classification |
Class B |
Table 23.11 lists the XT Model 286
system-unit part numbers.
Table 23.11 IBM XT-286
Model Part Numbers
Description |
Number |
XT Model 286 system unit, 6 MHz 0 wait
state, 640K, serial/parallel, 1.2M floppy drive, one 20M
hard disk |
5162286 |
Optional Accessories |
|
5 1/4-inch, half-height 360K drive |
6450325 |
3 1/4-inch, half-height 720K internal
drive |
6450258 |
3 1/2-inch, half-height 720K external
drive |
2683190 |
80287 math coprocessor option |
6450211 |
Enhanced Keyboard Accessories |
|
Clear keycaps (60) with paper inserts |
6341707 |
Blank light keycaps |
1351710 |
Blank dark keycaps |
1351728 |
Paper keycap inserts (300) |
6341704 |
Keycap removal tools (6) |
1351717 |
|