Many different types and styles of portable systems have been manufactured and sold over the past 18 to 20 years, including the following:

• Suitcase computers: Many of the earlier portable systems by Compaq, Osborne, Hewlett-Packard, etc. were in cases.
  
  
• Laptop computers: These computers were in cases and provided some external ports, many still used the same microdot monitors as the suitcase computers.
  
  
• Notebook computers: The currently popular type of portable system. These compuers provide all the capablilites of desktop computers with large, bright, and clear displays.
  
  
• Palmtop computers: The computers are also known as personal digital assistants or PDAs. The are currently only popular amoung high-tech businesses. The palmtop computers support sammler versions of word processors, spreadsheet applications, and other software and modem capabilities.
  
  

There are essentially three sources of power for portable PCs.

• Battery: An integral part of any portable PC, this is the primary source of power for portable computers.
  
  
• AC/DC adapter: Works like the power supply in a desktop PC. AC adapters are used to recharge the PC's battery system.
  
  
• Docking station: Provides power and more to the PC. In addition to the power, the docking station enables the PC to connect to full-sized expansion cards and additional ports. The docking station allows a portable PC to work as a desktop PC.
  
  

Portable PC battery types:

• Alkaline: This type of battery is used in some palmtop computers.
  
  
• NiCad: The standard of portable PC batteries, it is the heaviest, yet least expensive of the battery types used in notebooks. You must recharge NiCad batteries every 3 to 4 hours, which can take up to 12 hours. NiCad batteries have a charge/recharge cycle life around 1000 cycles.
  
  
• NiMH: The batteries are environmentally friendly because they don't contain heavy metals that can be toxic. These batteries store up to 50 percent more power than a NiCad of the same weight. The disadvantage of NiMH batteries is that they have a shorter life cycle: around 500 charge/discharge cycles.
  
  
• Li-Ion: Lithium is one of the lighter metals and is used to produce a very lightweight, long-life battery. It holds twice as much power as an NiCad battery for about half the weight.
  
  

     You can change PCMCIA or PC Cards without shutting down the portable system. This procedure is called hot-swapping. Two layers of software exist in the portable PC to detect and support a PCMCIA card when it is inserted into the portable PC:

• Socket services: A layer of BIOS level software that detects when a card is inserted or removed.
  
  
• Card services: Software that manages the assignment and allocation of system resources to the PC card, such as IRQ and I/O addresses, after the socket services has detected the card.
  
  

     A liquid crystal display (LCD) is used for the display output on portable PCs. An LCD has lower power requirements than the CRT monitors used on desktop compuers. This, combined with their ability to be configured into a flat panel are why they are used on notebook PCs. The two main types of LCD displays are:

• Active matrix: This is the type of LCD used on digital watches. This type of LCD display has a transistor for each pixel and creates a very crisp image that is easy to read from any angle with very good resolution. The downside is that all those transistors use power and can discharge a battery in less than two hours.
  
  
• Passive matrix: This type of LCD display has two groups of transistors: one along the top edge with one transistor for each vertical column of pixels, and the other along the left side of the display with one transistor for each horizontal row of pixels. Wires form a matrix interconnecting the transistor rows and columns. To darken a pixel, power is sent to the transistors on the same row and column as the pixel and down the wires to the intersection point where the pixel is located. This method uses less power but is slower and has a lower quality than Active matrix.