Portables Computers

You should be aware of not only the technology of a notebook or portable system, but any special power and communications specifications that come with it.

Separating The Formats

There are a couple different types of portable computers.  The first to arrive was called the suitcase computer, but were only for limited use because of their bulk and limited screen size.  Next came the Laptop computer, which were really misnamed as they were too bulky to be used on your lap.  They were however quite useful for mobile computing.

The current formats used in portable computing are the Notebook and Palmtop computers, or PDAs. (Personal Digital Assistant)  Notebooks are fully-functional computer systems meant for mobile computing, while PDAs are scaled-down versions that run limited operating systems and software applications.

These systems have different requirements and options from a normal system.  They differ in their power systems, their motherboards and peripherals, their expandability, and their viewing screens.  We will look at each one of these differences individually.

Power

The biggest difference with a portable system is it's power systems.  The idea of a portable is to make a computer that can go anywhere.  This involves cutting the leash, or in the case of a computer, the power cord.  This is done through the use of batteries.

Batteries for portable systems come in many types, although most are sticking with two common formats.  The oldest format is the Alkaline battery, which is now only used in PDAs.  Alkaline batteries are non-rechargeable, and are therefore ill-suited to work in notebooks.

In order to make batteries rechargeable, manufacturers began using Nickel-Cadmium (NiCad) batteries.  They can be recharged up to 1000 times (called it's life cycle), and are the cheapest and heaviest form of battery.

A step up from NiCad is Nickel-Metal Hydride.  NiMH batteries can give 40-60% longer battery life than NiCad, but only have about 500 charge cycles and cost about 35% more.  They are more environmentally-friendly than NiCad batteries.

The newest form of battery is the Lithium-Ion battery.  It holds about twice the charge of a NiCad battery and is lighter than a NiMH or NiCad battery.  It has the same number of charge cycles as a NiMH battery, but is about 50% more expensive.

Although it is common practice to run a portable on it's AC cord while recharging the battery, this is not recommended for NiCad batteries, and can shorten the life of NiMH batteries.  This is due to battery memory.  I'm going to use your cordless phone as an example, as we've all had one and cursed at one because of it's battery.

Let's say you charge your cordless phone, and then talk for a couple minutes.  You then but the phone back down on the charger.  It recharges the tiny portion of the battery used, and stops until it needs more.  You then make another quick call and replace the receiver.  It charges up a tiny portion, and stops.  After 15 to 20 charges in this manner, the battery will only charge the small portion that you've been using, neglecting the larger section of battery not used.  After a month or so, your battery will appear to be dead within minutes after a charge.  The battery has memorized the portion of the charge capacity being used, and doesn't acknowledge the charge in the other section.  This is called battery memory.

The only way to combat battery memory is to fully discharge a rechargeable battery before you charge it.  For a $15 cordless phone battery this is a mere inconvenience, but a $150 notebook battery will make you think twice.  Always use all the battery power you can, and fully charge the battery before using it again.

Motherboards And Peripherals

95% of the time you won't look inside a portable unless you have a specific task in mind.  This is because the motherboards of portable systems are generally non-upgradeable, and have few parts that can be replaced.  The only internal components you will ever change are the RAM and the Hard Drives.

To get at these parts, you'll be required to remove the top panel that holds the keyboard on the notebook.  This will expose the inner workings of the computer, and give you access to the RAM and Hard Drives.  You install these parts much the same way you would with a desktop computer, but the mounts and cabling will be different on each computer you see.

Portables are generally restricted to one hard drive and a small amount of RAM.  The motherboard that is inside the case is the only one that will fit, so the only time you'll be doing any more extensive work on the motherboard is to replace it with an identical motherboard.  The CPU and video card are soldered onto the board.

Expandability

As we said above, you can add RAM and Hard Drives to a notebook internally.  Notebooks also come with a system that allows you to add peripherals externally.  These systems are called Personal Computer Memory Card International Association cards, or PCMCIA (pic-um-see-ya) cards.  These cards allow you to add modems, memory, and other peripherals without having to crack the case on the notebook.

PCMCIA cards come in three varieties.  These three varieties differ by the thickness of the cards, as well as the number of pins they use to connect to the motherboard with.  PCMCIA cards are referred to as Hot-Swappable, meaning they can be inserted and removed without turning off the computer.  (Much like USB)  The three types of PCMCIA cards are;

PCMCIA uses two operating-system services to handle PCMCIA cards.  The first is called socket services (BIOS-Level), which detects when a component is added into the computer.  The second service is card services (OS-Level), which handles assigning I/O Addresses, IRQ's, and other system resources after the socket service detects the card.

Viewing Screens

Where a desktop system uses a monitor, a notebook or portable uses a Liquid Crystal Display, or LCD screen.  It uses much less power than a Cathode-Ray Tube (CRT) and is only an inch or so thick, as opposed to 12 to 16 inches for a CRT monitor.

There are two major forms of LCD screens used on notebooks.  The first is called Passive Matrix, which uses rows of wires horizontally and vertically that interconnect to form a matrix.  As power is sent through a horizontal and vertical wire, they light a pixel when they meet.  This uses very little power, but is slow to update and doesn't have the best image quality.

The second type is Active Matrix.  Each pixel has it's own transistor, and each pixel is controlled individually.  This gives the ability to to create fast-updating and high-quality images, but uses more power than a passive matrix.

There are different types of Active Matrix screens, but 90% are TFT (Thin-Film Transistor) models.  TFT screens are brighter and use less power than the other types, but are more expensive to produce.