Portable computers, like their desktop counterparts, have
evolved enormously since the days when the word portable could
mean as little as a case with a handle on it. Today, portable
systems can rival the performance of their desktop
counterparts in nearly every way, to the point at which many
systems are now being marketed as "desktop replacements" that
companies are providing to traveling employees as primary
systems. This chapter examines the types of portable computers
available and the technologies designed specifically for use
in mobile systems.
Portables started out as suitcase-sized systems that
differed from desktops mainly in that all of the components
were installed into a single case. Compaq was among the first
to market portable computers like these in the 1980s, and
although their size, weight, and appearance were almost
laughable when compared to today's portables, they were
cutting-edge technology for the time. The components
themselves were not very different from those in standard
computers. Most portable systems are now built using the
clamshell design that has become an industry standard (see
Figure 20.1), with nearly every component developed
specifically for use in mobile systems.
The computers have settled into a number of distinct roles
that now determine the size and capabilities of the systems
available. Traveling users have specific requirements of
portable computers, and the added weight and expense incurred
by additional features makes it less likely for a user to
carry a system more powerful than is needed.
Form Factors
There are three basic form factors that describe most of
the portable computers on the market today: laptops,
notebooks, and subnotebooks. The definitions of the three
types are fluid, however, with the options available on some
systems causing particular models to ride the cusp of two
categories. The categories are based primarily on size and
weight, but these factors have a natural relationship to the
capabilities of the system, because a larger case obviously
can fit more into it. The three form factors are described in
the following sections.
Laptops
As the original name coined for the clamshell-type portable
computer, the laptop is the largest of the three basic form
factors (see Figure 20.1). Typically, a laptop system weighs
seven pounds or more, and is approximately 9x12x2 inches in
size, although the larger screens now arriving on the market
are causing all portable system sizes to increase. Originally
the smallest possible size for a computer, laptops have today
become the high-end machines, offering features and
performance that are comparable to a desktop system.
FIG.
20.1 A laptop.
Indeed, many laptops are being positioned in the market
either as desktop replacement or as multimedia systems
suitable for delivering presentations on the road. Because of
their weight, they are typically used by sales people and
other travelers who require the features they provide,
although many laptops are now being issued to users as their
sole computer, even if they only travel from the office to the
home. Large displays, 16M or more of RAM, and hard drives up
to 2G in size are all but ubiquitous, with many systems now
carrying CD-ROM drives, on-board speakers, and connectivity
options that enable the use of external display, storage, and
sound systems.
As a desktop replacement, many laptops can be equipped with
a docking station that functions as the user's "home base,"
allowing connection to a network and the use of a full-size
monitor and keyboard. For a person that travels frequently,
this arrangement often works better than separate desktop and
portable systems, on which data must continually be kept in
sync. Naturally, you pay a premium for all of this
functionality. Cutting-edge laptop systems can now cost as
much as $6,000 to $7,000, more than three times the price of a
comparable desktop.
Notebooks
A notebook system is designed to be somewhat smaller than a
laptop in nearly every way: size, weight, features, and price.
Weighing 5 to 7 pounds, notebooks typically have smaller and
less capable displays and lack the high-end multimedia
functions of laptops, but they need not be stripped-down
machines. Many notebooks have hard drive and memory
configurations comparable to laptops, and some are equipped
with CD-ROM drives or sound capabilities.
Designed to function as an adjunct to a desktop system,
rather than a replacement, a notebook probably won't impress
your clients but can be a completely serviceable road machine.
Notebooks typically have a wide array of options, as they are
targeted at a wider audience, from the power user that can't
quite afford the top-of-the-line laptop, to the bargain hunter
that requires only basic services. Prices can range from less
than $2,000 to more than $4,000.
Subnotebooks
Subnotebooks are substantially smaller than both notebooks
and laptops, and are intended for users who must enter and
work with data on the road, as well as connect to the office
network. Weighing four to five pounds, and often less than an
inch thick, the subnotebook is intended for the traveler that
feels overburdened by the larger machines and doesn't need
their high-end capabilities.
Usually, the first component omitted in a subnotebook
design is the internal floppy drive, although some include
external units. You also will not find CD-ROM drives and other
bulky hardware components. However, many subnotebooks do
include large high-quality displays, plenty of hard drive
space, and a full-size keyboard (by portable standards).
As is common in the electronics world, devices become more
inexpensive as they get smaller, but only up to a certain
point, at which small size becomes a commodity and prices go
up. Some subnotebooks are intended (and priced) for the
high-end market, such as the executive that uses the system
for little else but e-mail and scheduling, but wants a
lightweight, elegant, and impressive-looking system.
Subnotebooks can cost as much as $4,000. Others are much
cheaper.
Portable System Designs
Obviously, portable systems are designed to be smaller and
lighter than desktops, and much of the development work that
has been done on desktop components has certainly contributed
to this end. The 2 1/2-inch hard drives typically used in
portables today are a direct extension of the size reductions
that have occurred in all hard drives over the past few years.
However, the other two issues that have created a need for the
development of new technologies specifically for portables are
power and heat.
Obviously, operating a computer from a battery imposes
system limitations that designers of desktop systems have
never had to consider. What's more, the demand for additional
features like CD-ROM drives and ever faster processors has
increased the power drain on the typical system enormously.
The problem of conserving power and increasing the system's
battery life is typically addressed in three ways:
- Low power components. Nearly all of the
components in today's portable systems are specifically
designed to use less power than their desktop
counterparts.
- Increased battery efficiency. Newer battery
technologies like lithium ion, while not keeping up with the
power requirements of increasingly loaded systems, are
making power supplies more consistent and reliable.
- Power management. Operating systems and utilities
that turn off specific system components, such as disk
drives when they are not in use, can greatly increase
battery life.
Perhaps a more serious problem than battery life is heat.
The moving parts in a computer, such as disk drives, generate
heat through friction, which must somehow be dissipated. In
desktop systems, this is usually accomplished by using fans to
continuously ventilate the empty spaces inside the system.
The worst culprit by far, however, as far as heat is
concerned, is the system processor. When they were first
released, the amount of heat generated by Intel's 80486 and
Pentium processors was a problem even in desktop systems. Heat
sinks and tiny fans mounted on top of the chip became standard
components in most systems.
Because many portable systems are now being designed as
replacements for desktops, users are not willing to compromise
on processing power, so the chips being manufactured for use
in portables have all of the speed and capabilities of the
desktop models. However, for reasons of power consumption,
noise, and space, there are often no fans in portable
computers and very little empty space within the case for
ventilation.
To address this problem, Intel has created a special method
for packaging its mobile processors that is designed to keep
heat output to a minimum. Other components are also designed
to withstand the heat within a portable computer, which is
usually greater than that of a desktop, in any case.
Upgrading and Repairing
Portables
The portable systems manufactured today are generally as
upgradeable and repairable as traditional desktop systems. In
fact, the process of replacing a device is often simpler than
on a desktop, because portable systems use modular components
with snap-in connectors that eliminate the need for ribbon
cables, mounting rails, and separate electrical connections.
Thus, common upgrades like adding memory and swapping out a
hard drive can usually be accomplished in seconds.
The problem with replacing components in portables is that
the hardware tends to be much less generic in portable systems
than it is in desktops. Except for PC Cards, which are
interchangeable by definition, and in some cases hard drives,
purchasing a component that is not specifically intended for
use in your exact system model can be risky.
In some cases, these compatibility problems are a matter of
simple logistics. Portable system manufacturers jam a great
deal of machinery into a very small case, and sometimes a new
device just will not fit in the space left by the old one.
This is particularly true of devices that must be accessible
from the outside of the case, like CD-ROM and floppy drives.
Keyboards and monitors, the most easily replaceable of desktop
components, are so completely integrated into the case of a
portable system that they may not be practically removed at
all.
In other cases, your upgrade path may be deliberately
limited by the options available in the system BIOS. For
example, a manufacturer may limit the hard drive types
supported by the system in order to force you to buy a
replacement drive from them, and not a third party. This is
something that you should check when shopping for a system by
asking whether the BIOS is upgradeable and finding out how
much the vendor charges for replacement components.
Most of the time, components for portable systems are sold
by referencing the system model numbers, even when third
parties are involved. If you look through a catalog for
desktop memory, for example, you see parts listed generically
by attributes like chip speed, form factor, and parity or
non-parity. The memory listings for portable systems, on the
other hand, will very likely consist of a series of systems
manufacturers' names and model numbers, plus the amount of
memory in the module.
There are always exceptions to the rule, of course. It is
even possible to purchase a basic laptop case and populate it
with individual components from various manufacturers.
However, purchasing compatible components that fit together
properly is certainly more of a challenge than it is for a
desktop system.
NOTE: Generally speaking, purchasing a
pre-assembled system from a reputable manufacturer is
strongly recommended, as is purchasing only replacement
components that are advertised as being specifically
designed for your system.
Portable System Hardware
From a technical standpoint, some of the components used in
portable systems are very similar to those in desktop
computers, while others are completely different. The
following sections examine the various subsystems found in
portable computers and how they differ from their
counterparts, discussed in the rest of this book.
Displays
Perhaps the most obvious difference between a portable
system and a desktop is the display screen. Gone is the box
with an emitter bombarding a concave glass tube with
electrons, In its place is a flat screen, the whole assembly
for which is more than half an inch thick. This is called an
LCD, or liquid crystal diode display.
Virtually all of the screens in portable systems today are
color, although monochromes were at one point the industry
standard, just as in standard monitors.
The display is usually the single most expensive component
in a portable system, often costing the manufacturer $1,000 or
more. In fact, it is sometimes more economical to replace the
entire computer rather than have a broken display replaced. In
the first laptops with color screens, the display was a poor
replacement for a standard VGA monitor. Today's portable
screens are much improved, and while not quite up to the
standards of a good monitor, provide excellent performance,
suitable even for graphic-intensive applications like bitmap
editing and videoconferencing.
The LCD display in a portable system is designed to operate
at a specific resolution. This is because the size of the
pixels on an LCD panel cannot be changed. On a desktop system,
the signal output from the video adapter can change the
resolution on the monitor, thus changing the number of pixels
created on the screen. Obviously, as you switch from a
resolution of 640x480 to 800x600, the pixels must be smaller
in order to fit into the same space.
An LCD panel, on the other hand, should be thought of as a
grid ruled off to a specified resolution, with transistors
controlling the color that is displayed by each individual
pixel. The arrangement of the transistors defines the two
major types of LCD displays used in portable systems today:
dual scan and active matrix.
Dual Scan Displays
The dual scan display, sometimes called a passive
matrix display, has an array of transistors running down
the x- and y-axes of two sides of the screen. The number of
transistors determines the screen's resolution. For example, a
dual scan display with 640 transistors along the x-axis and
480 along the y creates a grid like that shown in Figure 20.2.
Each pixel on the screen is controlled by the two transistors
representing its coordinates on the x- and y-axes.
FIG.
20.2 Dual scan LCD displays use a
combination of two transistors on intersecting axes to control
the color of each pixel.
If a transistor in a dual scan display should fail, a whole
line of pixels is disabled, causing a black line across the
screen. There is no solution for this problem other than to
replace the display or just live with it. The term dual
scan comes from the fact that the processor redraws half
of the screen at a time, which speeds up the refresh process
somewhat.
Dual scan displays are decidedly inferior to active matrix
screens. Dual scan displays tend to be dimmer, because the
pixels work by modifying the properties of reflected light
(either room light or, more likely, a white light source
behind the screen), rather than generating their own. Dual
scan panels are also prone to ghost images, and are difficult
to view from an angle, making it hard for two or more people
to share the same screen.
Of course, they are also far less expensive than active
matrix screens. These drawbacks are most noticeable during
video-intensive applications, such as presentations,
full-color graphics, video, or fast-moving games. For
computing tasks that consist largely of reading words on the
screen, like word processing and e-mail, the display is quite
serviceable, even for long periods of time.
The standard size for a dual scan display is 10 1/2 inches
(measured diagonally), running at 640x480, but there are now
some systems with 12.1-inch displays that run at 800x600
resolution. If you are familiar with the dual scan display of
an older portable, you will find that today's models are
greatly improved.
Active Matrix Displays
An active matrix display, also known as a TFT (thin film
transistor) display, differs from a dual scan in that it
contains a transistor for every pixel on the screen, rather
than just at the edges. The transistors are arranged on a grid
of conductive material, with each connected to a horizontal
and a vertical member (see Figure 20.3). Selected voltages are
applied by electrodes at the perimeter of the grid in order to
address each pixel individually.
FIG.
20.3 Active matrix LCD displays contain
a transistor for each pixel on the screen.
The pixels generate their own light for a brighter display.
Because every pixel is individually powered, each one
generates its own light of the appropriate color, creating a
display that is much brighter and more vivid than a dual scan
panel. The viewing angle is also greater, allowing multiple
viewers to gather around the screen; and refreshes are faster
and crisper, without the fuzziness of the dual scans, even in
the case of games or full-motion video.
On the downside, it should be no surprise that, with
480,000 transistors rather than 1,400 (on a 800x600 screen),
an active matrix display requires a lot more power than a dual
scan. It also drains batteries faster, and costs a great deal
more as well.
With all of these transistors, it is not uncommon for
failures to occur, resulting in displays with one or more
"dead pixels," due to malfunctioning transistors. Unlike a
dual scan display, in which the failure of a single transistor
causes an immediate and obvious flaw, a single black pixel is
far less noticeable. However, many buyers feel (and rightly
so) that a computer costing thousands of dollars should be
perfect and have attempted to return systems to the
manufacturer solely for this reason.
This has occurred often enough that many portable computer
manufacturers refuse to accept returns of systems for less
than a set number of bad pixels. This is another part of the
vendor's purchasing policy that you should check before
ordering a system with an active matrix display.
The 12.1-inch active matrix screen has become a standard on
high-end laptops, running at a resolution of 800x600 or even
1,024x768. Many portable systems now also include PCI bus
video adapters with 2M of RAM, providing extra speed, even at
16- or 24-bit color depths. These displays come very close to
rivaling that of a quality monitor and video adapter in a
desktop system.
Not to be accused of dragging their feet, however,
manufacturers are now bringing new systems to market with 13-
and even 14-inch TFT screens.
NOTE: Another flat screen technology, called
the gas plasma display, has been used in large display
screens and a few portables. Plasma displays provide a
CRT-quality picture on a thin flat screen using two glass
panes filled with a neon/xenon gas mixture. Unfortunately,
the displays require far more power than LCDs and have never
become a practical alternative for the portable computer
market.
Screen Resolution
The screen resolution of a portable system's display can be
an important factor in your purchasing decision. If you are
accustomed to working on desktop systems running at 800x600 or
1,024x768 pixels or more, you will find a 640x480 laptop
screen to be very restrictive. Remember that an LCD screen's
resolution is determined as much by the screen hardware as by
the drivers and the amount of video memory installed in the
system.
Some portables can use a virtual screen arrangement
to provide an 800x600 (or larger) display on a 640x480 pixel
screen. The larger display is maintained in video memory while
the actual screen displays only the portion that fits into a
640x480 window (see Figure 20.4). When you move the cursor to
the edge of the screen, the image pans, moving the 640x480
window around within the 800x600 display. The effect is
difficult to get used to, rather like a "scan and pan" video
tape of a wide-screen movie. The most serious problem with
this arrangement is that some manufacturers have advertised it
as an 800x600 display, without being more clear about the
actual nature of the display.
Color depth, on the other hand, is affected by video
memory, just as in a desktop system. To operate any LCD screen
in 16- or 24-bit color mode, you must have sufficient video
memory available. Portables typically have the video adapter
hardware permanently installed on the motherboard, leaving
little hope for a video memory upgrade. There are, however, a
few PC Card video adapters that you can use to connect to an
external monitor and increase the system's video
capabilities.
FIG.
20.4 A virtual screen lets you use a
small display to view a portion of a larger screen.
Processors
As with desktop systems, the majority of portables use
Intel multiprocessors, and the creation of chips designed
specifically for portable systems is a major part of the
company's development effort. The heat generated by Pentium
processors has been a concern since the first chips were
released. In desktop systems, the heat problem is addressed,
to a great extent, by computer case manufacturers. The use of
multiple cooling fans and better internal layout designs can
keep air flowing through the system to cool the processor,
which is usually also equipped with its own fan and heat
sink.
For developers of portable systems, however, not as much
can be accomplished with the case arrangement. So it was up to
Intel to address the problem in the packaging of the chip
itself. At the same time, users became increasingly unwilling
to compromise on the clock speed of the processors in portable
systems. Running a Pentium at 133 or 166MHz requires more
power and generates even more heat than the 75MHz Pentiums
that were originally designed for mobile use.
Tape Carrier Packaging
Intel's solution to the size and heat problems is the
tape carrier package (TCP), a method of
packaging Pentium processors for use in portable systems that
reduces the size, the power consumed, and the heat generated
by the chip. A Pentium mounted onto a motherboard using TCP is
much smaller and lighter than the standard PGA (pin grid
array) processors used in desktop systems. The 49mm square of
the PGA is reduced to 29mm in the TCP processor, the thickness
to approximately 1mm, and the weight from 55 grams to under 1
gram.
Instead of metal pins inserted into a socket on the
motherboard, a TCP processor is bonded to an oversized piece
of polyimide film, not unlike photographic film, using a
process called tape automated bonding (TAB), the same
process used to connect electrical connections to LCD panels.
The film, called the tape, is laminated with copper
foil that is etched to form the leads that will connect the
processor to the motherboard (see Figure 20.5). This is
similar to the way that electrical connections are
photographically etched onto a printed circuit board. Once the
leads are formed, they are plated with gold to guard against
corrosion, bonded to the processor chip itself, and then the
whole assembly is coated with a protective resin.
FIG.
20.5 A processor that is mounted using
the tape carrier package is attached to a piece of
copper-laminated film that replaces the pins used in standard
desktop processors.
After testing, the processor ships to the motherboard
manufacturer in this form. To mount the processor on a
motherboard, the tape is cut to the proper size and the ends
are folded into a modified gull wing shape that allows the
leads to be soldered to the motherboard while the processor
itself is suspended slightly above it (see Figure 20.6).
Before the actual soldering takes place, a thermally
conductive paste is added between the actual processor chip
and the motherboard. Heat can therefore be dissipated through
a sink on the underside of the motherboard itself while it is
kept away from the soldered connections. Because TCP
processors are soldered to the motherboard, they are not
usually upgradeable.
It should be noted that there are manufacturers of portable
systems who use standard desktop PGA processors, sometimes
accompanied by fans. Apart from a greatly diminished battery
life, systems like these can sometimes be too hot to touch
comfortably. For this reason, it is a good idea to determine
the exact model processor used in a system that you intend to
purchase, and not just the speed.
FIG.
20.6 The tape keeps the processor's
connections to the motherboard away from the chip itself and
allows the underside of the processor to be thermally bonded
to the motherboard.
Voltage Reduction
Intel has also taken measures to reduce the amount of power
used by its mobile processors, which extends battery life and
helps to reduce the output of heat. The pinouts of mobile
Pentiums have operated at 3.3v since the original 75MHz chip,
but the newer and faster models now incorporate a voltage
reduction technology that uses only 2.9v for the chip's
internal operations while retaining the 3.3v interface with
the motherboard.
This results in processors that use up to 40 percent less
power than their desktop counterparts without forcing systems
manufacturers to modify the electrical standards that they use
to design their machines.
Memory
Adding memory is one of the most common upgrades performed
on computers, and portables are no exception. However, most
portable systems are exceptional in the design of their memory
chips. Unlike desktop systems, in which there are only three
basic types of slots for additional RAM, there are literally
dozens of different memory chip configurations that have been
designed to shoehorn memory upgrades into the tightly packed
cases of portable systems.
Some portables use extender boards like the SIMMs and DIMMs
in desktop systems, while others use memory cartridges that
look very much like PC Cards, but which plug into a dedicated
IC (integrated circuit) memory socket. In any case, appearance
is not a reliable measure of compatibility. It is strongly
recommended that you install only memory modules that have
been designed for your system, in the configurations specified
by the manufacturer.
This recommendation does not necessarily limit you to
purchasing memory upgrades only from the manufacturer. There
are now many companies that manufacture memory upgrade modules
for dozens of different portable systems, by
reverse-engineering the original vendor's products. This adds
a measure of competition to the market, usually making
third-party modules much cheaper than those of a manufacturer
that is far more interested in selling new computers for
several thousand dollars rather than memory chips for a few
hundred.
NOTE: Some companies have developed memory
modules that exceed the original specifications of the
system manufacturer, allowing you to install more memory
than you could with the maker's own modules. Some
manufacturers, such as IBM, have certification programs to
signify their approval of these products. Otherwise, there
is an element of risk involved in extending the system's
capabilities in this way.
Inside the memory modules, the components are not very
different from those of desktop systems. Portables use the
same types of DRAM and SRAM as desktops, including the new
memory technologies like EDO (Enhanced Data Out). At one time,
portable systems tended not to have memory caches because the
SRAM chips typically used for this purpose generate a lot of
heat. Advances in thermal management have now made this less
of an issue, however, and you expect a high-end system to
include SRAM cache memory.
Hard Disk Drives
Hard disk drive technology is also largely unchanged in
portable systems, except for the size of the disks and their
packaging. Enhanced IDE drives are all but universal in
portable computers, with the exception of Macintosh, which
uses SCSI. Internal hard drives typically use 2 1/2-inch
platters, and are 12.5mm or 19mm tall, depending on the size
of the system.
As with memory modules, systems manufacturers have
different ways of mounting hard drives in the system, which
can cause upgrade compatibility problems. Some systems use a
caddy to hold the drive and make the electrical and data
connections to the system. This makes the physical part of an
upgrade as easy as inserting a new drive into the caddy and
then mounting it in the system. In other cases, you might have
to purchase a drive that has been specifically designed for
your system, with the proper connectors built into it.
In many portables, replacing a hard drive is much simpler
than in a desktop system. Multiple users can share a single
machine by snapping in their own hard drives, or you can use
the same technique to load different operating systems on the
same system.
The most important aspect of hard drive upgrades that you
must be aware of is the drive support provided by the system's
BIOS. The BIOS in some systems, and particularly older ones,
may offer limited hard drive size options. This is
particularly true if your system was manufactured before 1995
or so, when EIDE hard drives came into standard use. BIOSes
made before this time support a maximum drive size of 508M. In
some cases, flash BIOS upgrades may be available for your
system, which provide support for additional drives.
Another option for extending hard drive space is PC Card
hard drives. These are devices that fit into a type III PC
Card slot that can provide as much as 450M of disk space in a
remarkably tiny package (usually with a remarkably high
price). You can also connect external drives to a portable PC,
using a PC Card SCSI host adapter or specialized parallel port
drive interface. This frees you from the size limitations
imposed by the system's case, and you can use any size SCSI
drive you want, without concern for BIOS limitations.
Removable Media
Apart from hard disk drives, portable systems are now being
equipped with other types of storage media that can provide
access to large amounts of data. CD-ROM drives are now
available in many laptop and notebook systems while a few
include removable cartridge drives, such as Iomega's Zip
drive. This has been made possible by the Enhanced IDE
specifications that let other types of devices share the same
interface as the hard drive.
Another important issue is that of the floppy drive. Small
subnotebook systems usually omit the floppy drive to save
space, sometimes including an external unit. For certain types
of users, this may or may not be an acceptable inconvenience.
Many users of portables, especially those that frequently
connect to networks, have little use for a floppy drive. This
is becoming increasingly true even for the installation of
applications, as more and more software now ships on
CD-ROMs.
One of the features that is becoming increasingly common in
laptop and notebook systems is swappable drive bays that you
can use to hold any one of several types of components. This
arrangement lets you customize the configuration of your
system to suit your immediate needs. For example, when
traveling you might remove the floppy drive and replace it
with an extra battery, or install a second hard drive when
your storage needs increase.
PC Cards
In an effort to give laptop and notebook computers the kind
of expandability that users have grown used to in desktop
systems, the Personal Computer Memory Card International
Association (PCMCIA) has established several standards for
credit card-size expansion boards that fit into a small slot
on laptops and notebooks. The development of the PC Card
interface is one of the few successful feats of hardware
standardization in a market full of proprietary designs.
The PC Card standards, which were developed by a consortium
of more than 300 manufacturers (including IBM, Toshiba, and
Apple), have been touted as being a revolutionary advancement
in mobile computing. PC Card laptop and notebook slots enable
you to add memory expansion cards, fax/modems, SCSI adapters,
network interface adapters, and many other types of devices.
If your computer has PC Card slots that conform to the
standard developed by the PCMCIA, you can insert any type of
PC Card (built to the same standard) into your machine and
expect it to be recognized and usable.
Detailed online information about the standard is available
at
http://www.pccard.com
The promise of PC Card technology is enormous. There are
not only memory expansion cards, tiny hard drives, and
wireless modems, but also ISDN adapters, MPEG decoders,
network interface adapters, sound cards, CD-ROM controllers,
and even GPS systems that use global positioning satellites to
locate your exact position on the earth.
Originally designed as a standard interface for memory
cards, the PCMCIA document defines both the PC Card hardware
and the software support architecture used to run it. The PC
Cards defined in version 1 of the standard, called Type I, are
credit card size (3.4x2.1 inches) and 3.3mm thick. The
standard has since been revised to support cards with many
other functions. The third version, called PC Card
Specification--February 1995, defines three types of cards;
the only difference between each one is their thickness. This
was done to support the hardware for different card
functions.
Most of the PC Cards on the market today, such as modems
and network interface adapters, are 5mm thick Type II devices.
Type III cards are 10.5mm thick and are typically used for PC
Card hard drives. All of the card types are backwards
compatible; you can insert a Type I card into a Type II or III
slot. The standard PC Card slot configuration for portable
computers is two Type II slots, with one on top of the other.
This way, a single Type III card can be inserted, taking up
both slots but using only one of the connectors.
NOTE: There is also a Type IV PC Card, thicker
still than the Type III, that was designed for
higher-capacity hard drives. This card type is not
recognized by the PCMCIA, however, and is not included in
the standard document. There is, therefore, no guarantee of
compatibility between Type IV slots and devices, and they
should probably be avoided.
The latest version of the standard, published in March
1997, includes many features designed to increase the speed
and efficiency of the interface, such as:
- DMA (direct memory access) support
- 3.3v operation
- Support for APM (Advanced Power Management)
- Plug and Play support
- The PC Card ATA standard, which lets manufacturers use
the AT Attachment protocols to implement PC CARD hard disk
drives.
- Support for multiple functions on a single card (such as
a modem and a network adapter)
- The Zoomed Video (ZV) interface, a direct video bus
connection between the PC Card adapter and the system's VGA
controller, allowing high-speed video displays for
videoconferencing applications and MPEG decoders
- A thermal ratings system that can be used to warn users
of excessive heat conditions
- CardBus, a 32-bit interface that runs at 33MHz and
provides 32-bit data paths to the computer's I/O and memory
systems, as well as a new shielded connector that prevents
CardBus devices from being inserted into slots that do not
support the latest version of the standard. The first PC
Cards that use CardBus, in the form of network interface
cards made by 3com and others, are just now being released
to market. If you connect your portable computer to a
100Mbps network, CardBus will provide the high-speed
interface that, in a desktop system, would use PCI.
The PC Card itself usually has a sturdy metal case, and is
sealed except for the interface to the PCMCIA adapter in the
computer at one end, which consists of 68 tiny pinholes. The
other end of the card may contain a connector for a cable
leading to a telephone line, a network, or some other external
device.
The pinouts for the PC Card interface are shown in Table
20.1.
Table 20.1 Pinouts for a PCMCIA Card
Pin |
Signal Name |
1 |
Ground |
2 |
Data 3 |
3 |
Data 4 |
4 |
Data 5 |
5 |
Data 6 |
6 |
Data 7 |
7 |
-Card Enable 1 |
8 |
Address 10 |
9 |
-Output Enable |
10 |
Address 11 |
11 |
Address 9 |
12 |
Address 8 |
13 |
Address 13 |
14 |
Address 14 |
15 |
-Write Enable/-Program |
16 |
Ready/-Busy (IREQ) |
17 |
+5V |
18 |
Vpp1 |
19 |
Address 16 |
20 |
Address 15 |
21 |
Address 12 |
22 |
Address 7 |
23 |
Address 6 |
24 |
Address 5 |
25 |
Address 4 |
26 |
Address 3 |
27 |
Address 2 |
28 |
Address 1 |
29 |
Address 0 |
30 |
Data 0 |
31 |
Data 1 |
32 |
Data 2 |
33 |
Write Protect (-IOIS16) |
34 |
Ground |
35 |
Ground |
36 |
-Card Detect 1 |
37 |
Data 11 |
38 |
Data 12 |
39 |
Data 13 |
40 |
Data 14 |
41 |
Data 15 |
42 |
-Card Enable 2 |
43 |
Refresh |
44 |
RFU (-IOR) |
45 |
RFU (-IOW) |
46 |
Address 17 |
47 |
Address 18 |
48 |
Address 19 |
49 |
Address 20 |
50 |
Address 21 |
51 |
+5V |
52 |
Vpp2 |
53 |
Address 22 |
54 |
Address 23 |
55 |
Address 24 |
56 |
Address 25 |
57 |
RFU |
58 |
RESET |
59 |
-WAIT |
60 |
RFU (-INPACK) |
61 |
-Register Select |
62 |
Battery Voltage Detect 2 (-SPKR) |
63 |
Battery Voltage Detect 1 (-STSCHG) |
64 |
Data 8 |
65 |
Data 9 |
66 |
Data 10 |
67 |
-Card Detect 2 |
68 |
Ground |
PC Card Software Support
PC Cards are by definition hot-swappable, meaning
that you can remove a card from a slot and replace it with a
different one without having to reboot the system. If your PC
Card devices and your operating system conform to the Plug and
Play standard, simply inserting a new card into the slot
causes the appropriate drivers for the device to be loaded and
configured automatically.
To make this possible, two separate software layers are
needed on the computer that provide the interface between the
PCMCIA adapter (that controls the card slots) and the
applications that use the services of the PC Card devices (see
Figure 20.7). These two layers are called Socket
Services and Card Services. A third module, called
an enable, actually configures the settings of the PC
Cards themselves.
FIG.
20.7 The Card and Socket Services allow
an operating system to recognize the PC Card inserted into a
slot and configure the appropriate system hardware resources
for the device.
Socket Services
The PCMCIA adapter that provides the interface between the
card slots and the rest of the computer is one of the only
parts of the PCMCIA architecture that is not standardized.
There are many different adapters available to portable
systems manufacturers and, as a result, an application or
operating system cannot address the slot hardware directly, as
it can a parallel or serial port.
Instead, there is a software layer called Socket Services
that is designed to address a specific make of PCMCIA adapter
hardware. The Socket Services software layer isolates the
proprietary aspects of the adapter from all of the software
operating above it. The communications between the driver and
the adapter may be unique, but the other interface, between
the Socket Services driver and the Card Services software, is
defined by the PCMCIA standard.
Socket Services can take the form of a device driver, a TSR
program run from the DOS prompt (or the AUTOEXEC.BAT file), or
a service running on an operating system like Windows 95 or
Windows NT. It is possible for a computer to have PC Card
slots with different adapters, as in the case of a docking
station that provides extra slots in addition to those in the
portable computer itself. In this case, the computer can run
multiple Socket Services drivers, all of which communicate
with the same Card Services program.
Card Services
The Card Services software communicates with Socket
Services and is responsible for assigning the appropriate
hardware resources to PC Cards. PC Cards are no different from
other types of bus expansion cards, in that they require
access to specific hardware resources in order to communicate
with the computer's processor and memory subsystems. If you
have ever inserted an ISA network interface card into a
desktop system, you know that you must specify a hardware
interrupt, and maybe an I/O port or memory address in order
for the card to operate.
A PC Card network adapter requires the same hardware
resources, but you do not manually configure the device using
jumpers or a software utility as you would an ISA card. The
problem is also complicated by the fact that the PCMCIA
standard requires that the computer be able to assign hardware
resources to different devices as they are inserted into a
slot. Card Services addresses this problem by maintaining a
collection of various hardware resources that it allots to
devices as needed, and reclaims as the devices are
removed.
If, for example, you have a system with two PC Card slots,
the Card Services software might be configured to use two
hardware interrupts, two I/O ports, and two memory addresses,
whether any cards are in the slots at boot time or not. No
other devices in the computer can use those interrupts. When
cards are inserted, Card Services assigns configuration values
for the settings requested by the devices, ensuring that the
settings allotted to each card are unique.
Card Services is not the equivalent of Plug and Play,
although the two may seem similar. In fact, in Windows 95,
Card Services obtains the hardware resources that it assigns
to PC Cards using Plug and Play. For other operating systems,
the resources may be allotted to the Card Services program
using a text file or command-line switches. In a non-Plug and
Play system, you must configure the hardware resources
assigned to Card Services with the same case that you would
configure an ISA board. Although Card Services won't allow two
PC Cards to be assigned the same interrupt, there is nothing
in the PCMCIA architecture to prevent conflicts between the
resources assigned to Card Services and those of other devices
in the system.
You can have multiple Socket Services drivers loaded on one
system, but there can be only one Card Services program.
Socket Services must always be loaded before Card
Services.
Enablers
One of the oldest rules of PC configuration is that the
software configuration must match that of the hardware. For
example, if you configure a network interface card to use
interrupt 10, then you must also configure the network driver
to use the same interrupt, so that it can address the device.
Today, this can be confusing because most hardware is
configured not by physically manipulating jumpers or DIP
switches, but by running a hardware configuration utility.
In spite of their other capabilities, neither Socket
Services nor Card Services are capable of actually configuring
the hardware settings of PC Cards. This job is left to a
software module called an enabler. The enabler receives
the configuration settings assigned by Card Services and
actually communicates with the PC Card hardware itself to set
the appropriate values.
Like Socket Services, the enabler must be designed to
address the specific PC Card that is present in the slot. In
most cases, a PCMCIA software implementation includes a
generic enabler, that is, one that can address many
different types of PC Cards. This, in most cases, lets you
insert a completely new card into a slot and have it be
recognized and configured by the software.
The problem with a generic enabler, and with the PCMCIA
software architecture in general, is that it requires a
significant amount of memory to run. Because it must support
many different cards, a generic enabler can require 50K of RAM
or more, plus another 50K for the Card and Socket Services.
For systems running DOS (with or without Windows 3.1), this is
a great deal of conventional memory, just to activate one or
two devices. Once installed and configured, the PC Card
devices may also require additional memory, for network, SCSI,
or other device drivers.
NOTE: Windows 95 is definitely the preferred
operating system for running PC Card devices. The
combination of its advanced memory management, its Plug and
Play capabilities, and the integration of the Card and
Socket Services into the operating system makes the process
of installing a PC Card usually as easy as inserting it into
the slot.
When memory is scarce, there can be an alternative to the
generic enabler. A specific enabler is designed to
address only a single specific PC Card, and uses much less
memory for that reason. Some PC Cards ship with specific
enablers that you can use in place of a generic enabler.
However, it is also possible to use a specific enabler when
you have a PC Card that is not recognized by your generic
enabler. You can load the specific enabler to address the
unrecognized card, along with the generic enabler to address
any other cards that you may use. This practice, of course,
increases the memory requirements of the software.
Finally, you can avoid the overhead of generic enablers and
the Card and Socket Services entirely, by using what is known
as a point enabler. A point enabler is a software
module that is included with some PC Cards that addresses the
hardware directly, eliminating the need for Card and Socket
Services. As a result, the point enabler removes the
cap-ability to hot swap PC Cards and have the system
automatically recognize and configure them. If, however, you
intend to use the same PC Cards all of the time, and have no
need for hot swapping, point enablers can save you a
tremendous amount of memory.
Keyboards
Unlike desktop systems, portables have keyboards that are
integrated into the one-piece unit. This makes them difficult
to repair or replace. The keyboard should also be an important
element of your system purchasing decision, because
manufacturers are forced to modify the standard 101-key
desktop keyboard layout in order to fit in a smaller case.
The numeric keypad is always the first to go in a portable
system's keyboard. Usually, its functionality is embedded into
the alphanumeric keyboard and activated by a Function key
combination. The Function (or Fn) key is an additional control
key used on many systems to activate special features like the
use of an alternate display or keyboard.
Most systems today have keyboards that approach the size
and usability of desktop models. This is a vast improvement
over some older designs in which keys were reduced to a point
at which you could not comfortably type with both hands.
Standard conventions like the "inverted T" cursor keys were
modified, causing extreme user displeasure.
Some systems still have half-sized function keys, but one
of the by-products of the larger screens found in many of
today's portable systems is more room for the keyboard. Thus,
many manufacturers are taking advantage of the extra space.
Pointing Devices
As with the layout and feel of the keyboard, pointing
devices are a matter of personal taste. Most portable systems
have pointing devices that conform to one of the three
following types (see Figure 20.8):
- Trackball. A small ball (usually about 1/2-inch)
embedded partially in the keyboard below the space bar, that
is rolled by the user. While serviceable and accurate,
trackballs have become unpopular, primarily due to their
tendency to gather dust and dirt in the well that holds the
ball, causing degraded performance.
- Trackpoint. Developed by IBM and adopted by many
other manufacturers, the trackpoint is a small (about
1/4-inch) rubberized button located between the G, H, and B
keys of the keyboard. It looks like a pencil eraser and can
be nudged in any direction to move the cursor around the
screen. The trackpoint is very convenient because you can
manipulate it without taking your hands off of the keyboard.
On some earlier models, the rubber cover tended to wear off
after heavy use, and replacements were mysteriously
unavailable. Newer versions are made of sturdier
materials.
- Trackpad. The most recent development of the
three, the trackpad is an electromagnetically sensitive pad,
usually about 1x2 inches, that responds to the movement of a
finger across its surface. Mouse clicks are simulated by
tapping the pad. Trackpads have great potential, but tend to
be overly sensitive to accidental touches, causing undesired
cursor movements and especially unwanted mouse clicks.
Trackpads are also sensitive to humidity and moist fingers,
resulting in unpredictable performance.
FIG.
20.8a Portable systems are usually equipped with
one (or two) of these three pointing devices.
FIG.
20.8b
FIG.
20.8c
The trackpad is still a relatively new innovation to the
portable system market (although the technology has been
around for years), and some systems allow users a choice by
providing both a trackpoint and a trackpad. Unfortunately, on
most of the systems that do this, the two devices use the same
interrupt, forcing you to select one device or the other in
the system BIOS, rather than letting you use both at the same
time.
Another important part of the pointer arrangement is the
location of the primary and secondary buttons. Some systems
locate the buttons in peculiar configurations that require
unnatural contortions to perform a click-and-drag operation.
Pointing devices are definitely a feature of a portable system
that you should test drive before you make a purchase. As an
alternative, remember that nearly all portables have a serial
port that you can use to attach an external mouse to the
system, when your workspace permits.
Batteries
Battery life is one of the biggest complaints that users
have about portable systems. Although a great deal has been
done to improve the power management capabilities of today's
portable computers, the average hardware configuration has
grown enormously at the same time. The efficiency of a
computer's power utilization may have doubled in the last two
years, but the power required by the system in order to run a
faster processor and a CD-ROM drive has also doubled, leaving
the battery life the same as it was before.
Battery Types
The battery technology also has a role in the issue, of
course. Most portable systems today use one of three battery
types:
- Nickel Cadmium (NiCad). As the oldest of the
three technologies, nickel cadmium batteries are rarely used
in portable systems today, because of their shorter life and
their sensitivity to improper charging and discharging.
NiCad batteries hold a charge well when not in use, but the
life of the charge can be severely shortened if the battery
is not fully discharged before recharging, or if it is
overcharged.
- Nickel Metal-Hydride (NiMH). More expensive than
NiCads, NiMH batteries have a slightly longer life (about 50
percent), and are less sensitive to improper charging and
discharging. They do not hold a charge as well as NiCad
batteries when not used, and usually cannot be recharged as
many times. NiMH batteries are still used in most portable
systems, usually those in the lower end of the price
range.
- Lithium-Ion (Li-Ion). As the current industry
standard, Li-Ion batteries are longer-lived than either of
the other two technologies, cannot be overcharged, and hold
a charge well when not in use. Li-Ion batteries can also
support the heavy duty power requirements of today's
high-end systems. Unlike NiCad and NiMH batteries, which can
be used in the same system without modification to the
circuitry, Li-Ion batteries can only be used in systems
specifically designed for them. Inserting a Li-Ion battery
into a system designed for a NiCad or NiMH can result in a
fire. As the most expensive of the three technologies,
Li-Ion batteries are usually found in high-end
systems.
- Lithium Polymer. This is a fourth battery type
that has been in development for several years, but which
has not yet appeared on the market. Lithium polymer
batteries can be formed into thin flat sheets and placed
behind the LCD panel of a portable computer, thus providing
a battery life 40 percent longer than that of Li-Ion
batteries with far less weight. If this technology is
implemented in portable systems, it will represent a sorely
needed innovation in mobile computing.
NOTE: All of the battery types in use today
function best when they are completely discharged before
being recharged. Lithium Ion batteries are affected the
least by incomplete discharging, but the effect on the life
of future charges is still noticeable. When storing charged
batteries, refrigerating them helps them to retain their
charges for longer periods.
Unfortunately, buying a portable computer with a Li-Ion
battery does not necessarily mean that you will realize a
longer charge life. Power consumption depends on the
components installed in the system, the power management
capabilities provided by the system software, and the size of
the battery itself. Some manufacturers, for example, when
moving from NiMH to Li-Ion batteries, see this as an
opportunity to save some space inside the computer. They
decide that since they are using a more efficient power
storage technology, they can make the battery smaller and
still deliver the same performance.
Unfortunately, battery technology trails behind nearly all
of the other subsystems found in a portable computer, as far
as the development of new innovations is concerned. Power
consumption in mobile systems has risen enormously in recent
years, and power systems have barely been able to keep up. On
a high-end laptop system, a battery life of two hours is very
good, even with all of the system's power management features
activated.
One other way that manufacturers are addressing the battery
life problem is by designing systems that are capable of
carrying two batteries. The inclusion of multipurpose bays
within the system's case enables users to replace the floppy
or CD-ROM drive with a second battery pack, effectively
doubling the computer's power supply.
Power Management
There are various components in a computer that do not need
to run continuously while the system is turned on. Mobile
systems often conserve battery power by shutting down these
components based on the activities of the user. If, for
example, you open a text file in an editor, the entire file is
read into memory and there is no need for the hard drive to
spin while you are working on the file.
After a certain period of inactivity, a power management
system can park the drive heads and stop the platters from
spinning until you save the file to disk or issue any other
call that requires its service. Other components, such as
floppy and CD-ROM drives and PC Cards, can be powered down
when not in use, resulting in a significant reduction of the
power needed to run the system.
Most portables also have systemic power saver modes that
suspend the operation of the entire system when it is not in
use. The names assigned to these modes can differ, but there
are usually two system states that differ in that one
continues to power the sys-tem's RAM while one does not.
Typically, a "suspend" mode shuts down virtually the entire
system after a preset period of inactivity except for the
memory. This re- quires only a small amount of power and
allows the system to be re-awakened almost
instantaneously.
Portable systems usually have a "hibernate" mode as well,
which writes the current contents of the system's memory to a
special file and then shuts down the system, erasing memory as
well. When the computer is reactivated, the contents of the
file are read back into memory and work can continue. The
reactivation process takes a bit longer in this case, but the
system conserves more power by shutting down the memory array.
NOTE: The memory swap file used for hibernate
mode may, in some machines, be located in a special
partition on the hard drive, dedicated to this purpose. If
you inadvertently destroy this partition, you may need a
special utility from the system manufacturer to re-create
the file.
In most cases, these functions are defined by the APM
(Advanced Power Management) standard, a document developed
jointly by Intel and Microsoft that defines an interface
between an operating system power management policy driver and
the hardware-specific software that addresses devices with
power management capabilities. This interface is usually
implemented in the system BIOS.
However, as power management techniques continue to
develop, it becomes increasingly difficult for the BIOS to
maintain the complex information states needed to implement
more advanced functions. There is, therefore, another standard
under development by Intel, Microsoft, and Toshiba called
ACPI (the Advanced Configuration and Power Interface),
which is designed to implement power management functions in
the operating system.
Placing power management under the control of the OS allows
for a greater interaction with applications. For example, a
program can indicate to the operating system which of its
activities are crucial, forcing an immediate activation of the
hard drive, and which can be delayed until the next time that
the drive is activated for some other reason.
Peripherals
There are a great many add-on devices available for use
with portable systems, which provide functions that cannot
practically or economically be included inside the system
itself. Many of the most common uses for portable systems may
require additional hardware, either because of the computer's
location or the requirements of the function itself. The
following sections discuss some of the most common peripherals
used with portable systems.
External Displays
High-end laptop systems are often used to host
presentations to audiences that can range in size from the
boardroom to the auditorium. For all but the smallest groups
of viewers, some means of enlarging the computer display is
needed. Most portable systems are equipped with a standard VGA
jack that allows the connection of an external monitor.
Systems typically allow the user to choose whether the
display should be sent to the internal, the external, or both
displays, as controlled by a keystroke combination or the
system BIOS. Depending on the capabilities of the video
display adapter in the computer, you may be able to use a
greater display resolution on an external monitor than you
would on the LCD panel.
For environments where the display of a standard monitor is
not large enough, there are several alternatives, as discussed
in the following sections.
Overhead LCD Display Panels
An LCD display panel is something like the LCD screen in
your computer except that there is no back on it, making the
display transparent. The display technologies and screen
resolution options are the same as those for the LCD displays
in portable systems, although most of the products on the
market use active matrix displays.
You use an LCD panel by placing it on an ordinary overhead
projector, causing the image on the panel to be projected onto
a screen (or wall). Because they are not intended solely for
use with portable systems, these devices typically include a
pass-through cable arrangement, allowing a connection to a
standard external monitor, as well as the panel.
While they are serviceable for training and internal use,
overhead display panels do not usually deliver the depth and
vibrancy of color that can add to the excitement of a sales
presentation. The quality of the image is also dependent on
the brightness of the lamp used to display it. While the panel
itself is fairly small and lightweight, overhead projectors
frequently are not. If a projector is already available at the
presentation site, the LCD panel is a convenient way of
enlarging your display. If, however, you are in a position
where you must travel to a remote location and supply the
overhead projector yourself, you are probably better off with
a self-contained LCD projector.
Overhead display panels are not cheap. You will probably
have to pay more for one than you paid for your computer.
However, on a few models of the IBM ThinkPad, you can remove
the top cover that serves as the back of the display and use
the LCD screen as an overhead panel.
LCD Projectors
An LCD projector is essentially a self-contained
unit that is a combination of a transparent display panel and
a projector. The unit connects to a VGA jack like a regular
monitor and frequently includes speakers that connect with a
separate cable. Not all LCD projectors are portable; some are
intended for permanent installations. The portable model
varies in weight, display technologies, and the brightness of
the lamp, which is measured in lumens.
A 16-pound unit delivering 300-400 lumens is usually
satisfactory for a conference room environment; a larger room
may require a projector delivering 500 lumens or more,
weighing up to 25 pounds. LCD projectors tend to deliver
images that are far superior to those of overhead panels; and
they offer a one-piece solution to the image-enlargement
problem. However, you have to pay dearly for the convenience.
Prices of LCD projectors can range from $4,000 to well over
$10,000, but if your business relies on your presentations,
the cost may be justified.
TV-Out
One of the simplest display solutions is a feature that is
being incorporated into many of the high-end laptop systems on
the market today. It allows you to connect the computer to a
standard television set. Called TV-out, various systems
provide support for either the North American NTSC television
standard, the European PAL standard, or both. Once connected,
a software program lets you calibrate the picture on the TV
screen.
TV-out is becoming a popular feature on high-end video
adapters for desktop systems, as well as portables. There are
also some manufacturers that are producing external boxes that
plug into any computer's VGA port and a television set, to
provide an external TV display solution. The products convert
the digital VGA signal to an analog output that typically can
be set to use the NTSC or PAL standard.
Obviously, TV-out is an extremely convenient solution, as
it provides an image size that is limited only by the type of
television available, costs virtually nothing, and adds no
extra weight to the presenter's load (unless you have to bring
the TV yourself). You can also connect your computer to a VCR
and record your presentation on standard videotape. However,
the display resolution of a television set does not approach
that of a computer monitor, and the picture quality suffers as
a result. This is particularly noticeable when displaying
images that contain a lot of text, such as presentation slides
and Web sites. It is recommended that you test the output
carefully with various size television screens before using
TV-out in a presentation environment.
Docking Stations
Now that many portable systems are being sold as
replacements for standard desktop computers, docking stations
are becoming increasingly popular. A docking station is a
desktop unit to which you attach (or dock) your portable
system when you are at your home or office. At the very least,
a docking station provides an AC power connection, a full-size
keyboard, a mouse, a complete set of input and output ports,
and a VGA jack for a standard external monitor.
Once docked, the keyboard and display in the portable
system are deactivated, but the other components, particularly
the processor, memory, and hard drive, remain active. You are
essentially running the same computer, but using a standard
full-size desktop interface. Docking stations can also contain
a wide array of other features, such as a network interface
adapter, external speakers, additional hard disk or CD-ROM
drives, additional PC Card slots, and a spare battery
charger.
An operating system like Windows 95 can maintain multiple
hardware profiles for a single machine. A hardware profile is
a collection of configuration settings for the devices
accessible to the system. To use a docking station, you create
one profile for the portable system in its undocked state, and
another that adds support for the additional hardware
available while docked.
The use of a docking station eliminates much of the tedium
involved in maintaining separate desktop and portable systems.
With two machines, you must install your applications twice,
and continually keep the data between the two systems
synchronized. This is traditionally done using a network
connection or the venerable null modem cable (a crossover
cable used to transfer files between systems by connecting
their parallel or serial ports). With a docking station and a
suitably equipped portable, you can achieve the best of both
worlds.
Docking stations are highly proprietary items that are
designed for use with specific computer models. Prices vary
widely depending on the additional hardware provided, but
since a docking station lacks a CPU, memory, and a display,
the cost is usually not excessive.
Connectivity
One of the primary uses for portable computers is to keep
in touch with the home office while traveling by using a
modem. Because of this, many hotels and airports are starting
to provide telephone jacks for use with modems, but there are
still many places where finding a place to plug into a phone
line can be difficult. There are products on the market,
however, that can help you to overcome these problems, even if
you are traveling overseas.
Line Testers
Many hotels use digital PBXs for their telephone systems,
which typically carry more current than standard analog lines.
This power is needed to operate additional features on the
telephone itself, such as message lights and LCD displays.
This additional current can permanently damage your modem
without warning, and unfortunately, the jacks used by these
systems are the same standard RJ-11 connectors used by
traditional telephones.
To avoid this problem, you can purchase a line-testing
device for about $50 that plugs into a wall jack and measures
the amount of current on the circuit. It then informs you
whether or not it is safe to plug in your modem.
Acoustic Couplers
On those occasions when you cannot plug your modem into the
phone jack, or when there is no jack available, such as at a
pay phone, the last resort is an acoustic coupler. The
acoustic coupler is an ancient telecommunications device that
predates the system of modular jacks used to connect
telephones today. To connect to a telephone line, the coupler
plugs into your modem's RJ-11 jack at one end and clamps to a
telephone handset at the other end. A speaker at the
mouthpiece and a microphone at the earpiece allow the audible
signals generated by the modem and the phone system to
interact.
The acoustic coupler may be an annoying bit of extra
baggage to have to carry with you, but it is the one foolproof
method for connecting to any telephone line without having to
worry about international standards, line current, or
wiring.
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