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Portable System Components

Portable computers have two ideal characteristics: They are compact and lightweight. Portable computer designers work constantly to decrease the size and power consumption of all the computer's components. Special low-power–consumption ICs and disk drives have been developed to extend their battery life.

Likewise, their cases have been designed to be as small as possible while providing as many standard features as possible. Figure 3.1 shows the inside of a typical portable computer. Notice how the components are interconnected by the design. The system board is designed so that it wraps around other components whose form factors cannot be altered—such as the disk-drive units. The components also tend to be layered in portable designs. Disk drives cover portions of the system board, while the keyboard unit covers nearly everything. The internal battery may slide into a cutout area of the system board, or more likely, it may be located beneath the system board.

Figure 3.1Figure 3.1 Inside a portable computer.

Portable System Boards

A typical notebook system board is depicted in Figure 3.2. The first thing you should notice about it is its unusual shape. As noted earlier, system boards for portable computers are not designed to fit a standardized form factor. Instead, they are designed to fit around all the components that must be installed in the system. Therefore, system boards used in portable computers tend to be proprietary to the model they are designed for. Mounting hole positions are determined by where they will best suit the placement of the other system components.

Figure 3.2Figure 3.2 Typical notebook system board.

The second item to notice is that none of the "standard" expansion slots or adapter cards are present on the portable's system board. These system-board designs typically include the standard I/O and video circuitry as an integral part of the board. They also provide the physical connections for the unit's parallel and serial I/O ports, as well as onboard connectors for the disk drives, display unit, and keyboard units.

The computer's external I/O connections, such as serial- and parallel-port connectors, are arranged on the system board so that they align with the corresponding openings in the portable case. It would be highly unlikely that a system board from another portable would match these openings. On the maintenance side, a blown parallel-port circuit would require that the entire system board be replaced to correct the problem. In a desktop unit, a simple I/O card could be installed in an expansion slot to overcome such a situation.

Installing Portable Memory

It is not a common practice for notebook and other portable computer manufacturers to use traditional SIMM and DIMM modules in their designs. Instead, These types of computers routinely use smaller SODIMM and MicroDIMM form-factor memory modules. Both of these memory formats are described in more detail in Chapter 14, "Random Access Memory."

The key to upgrading or replacing internal RAM in a portable computer can be found in its documentation. Only memory modules recommended by the portable manufacturer should be installed, and only in the configurations suggested.

The voltage-level support for the memory devices in portable computers is critical. Using RAM devices that electrically overload this supply causes memory errors to occur.

If the type of RAM device being installed is not one of the recommended types, the notebook might not be able to recognize the new memory. If the new RAM is being added to expand the existing banks of memory, the system might not recognize this additional RAM. The problem will show up in the form of a short memory count during the POST routines. However, if only the new RAM type is installed, the system could present a number of different symptoms, including

  • Not working at all

  • Giving beep-coded error messages

  • Producing soft memory errors

  • Producing short memory counts in the POST

  • Locking up while booting the operating system

As with disk drives, changing memory in a portable PC involves disassembling the computer case. Figure 3.3 shows the replacement of a SODIMM module in a particular notebook computer. The location and process of accessing the memory in the unit vary from manufacturer to manufacturer and model to model.


Know why notebook computers show short memory counts during the bootup process.

Figure 3.3Figure 3.3 Replacing a SODIMM module.

In notebook computers, you can increase memory capabilities by installing PC Card–based memory cards, described later in this chapter. These memory units can increase the portable computer's memory capabilities without your taking it apart. In addition, they can be removed when additional memory space is not in high demand. A newer memory add-on technology that has found some favor in the notebook computer arena is the USB plug-in memory module.

Portable Display Types

Portable computers continue to gain popularity due to their ability to travel with the user. This has been made possible by the development of different flat-panel display technologies. Notebook and laptop computers use non-CRT displays, such as liquid crystal display (LCD) and gas-plasma panels. These display systems are well suited to the portability needs of portable computers. They are much lighter and more compact than CRT monitors and require much less electrical energy to operate. Both types of display units can be operated from batteries.


Know that notebook display panels are powered by low-voltage DC power sources such as a battery or converter.

Liquid Crystal Displays

The most common flat-panel displays used with portable PCs are liquid crystal displays. They are relatively thin, flat, and lightweight, and require very little power to operate. In addition to reduced weight and improved portability, these displays offer better reliability and longer life than CRT units.

The LCD panel is constructed by placing thermotropic liquid crystal material between two sheets of glass. A set of electrodes is attached to each sheet of glass. Horizontal (row) electrodes are attached to one glass plate; vertical (column) electrodes are fitted to the other plate. These electrodes are transparent and let light pass through. A picture element, or pixel, is created in the liquid crystal material at each spot where a row and a column electrode intersect. A special plate called a polarizer is added to the front and back of the display.

The complete LCD panel is mounted in a frame that also contains the control circuitry for the panel's electrode matrix. In a notebook computer, the frame is mounted between the two halves of its flip-up display housing, as illustrated in Figure 3.4. The display physically attaches to the body of the notebook by a pair of built-in hinges. The display is free to rotate around a pair of rods in the main body. Electrically, a single cable is generally used to connect the entire panel assembly to the system board using a plug-and-socket arrangement.

Figure 3.4Figure 3.4 LCD panel connections.

When an LCD panel fails, the most common repair is to replace the entire display panel/housing assembly. To replace the LCD panel, you must use an identical panel to ensure that it fits the plastic display housing. The upper half of the notebook body must be removed to provide access for plugging the display's signal cable into the system board.


Be aware that the most common LCD repair is replacement.


A typical notebook keyboard is illustrated in Figure 3.5.

Figure 3.5Figure 3.5 A typical 84-key notebook keyboard.

Because portable keyboards tend to be more compact than the detachable models used with desktop units, many of its keys are typically given dual or triple functions. The portable keyboard normally contains an Fn function key. This key activates special functions on the portable, such as display brightness and contrast. Other common Fn functions include Suspend mode activation and LCD/external-CRT device selection.

Newer keyboard models may also include left and right Windows keys (Win keys) and an application key, as identified in Figure 3.6. The WIN keys are located next to the Alt keys and provide specialized Windows functions, as described in Table 3.1. Similarly, the application key is located near the right Win key, or the Ctrl key, and provides context-sensitive help for most applications.

Figure 3.6Figure 3.6 Win and application keys.

Table 3.1 Win Key Definitions

Win Key Definitions

Most portables offer standard connectors to enable full-size keyboards and VGA monitors to be plugged in, as shown in Figure 3.7. The VGA connector is usually the standard 15-pin D-shell type, whereas the external keyboard connector is generally the 6-pin mini-DIN (PS/2) type. When an external keyboard is plugged in, the built-in keyboard is disabled. The portable's software may allow both displays to remain active while the external monitor is connected.

Figure 3.7Figure 3.7 Attaching standard I/O devices.


In some applications, such as notebook computers, it is desirable to have a pointing device that does not require a surface to be moved across. You can think of the trackball as an inverted mouse that allows the user to directly manipulate it. Trackballs, like the one depicted in Figure 3.8, may be separate units that sit on a desk or clip to the side of the computer and connect to one of the system's serial ports. In many laptop and notebook computers, trackballs are frequently built directly into the system housing and connected directly to its I/O circuitry. Like mice, trackballs may come with one to three buttons.

Figure 3.8Figure 3.8 A trackball unit.

Touch Pads

Hewlett-Packard introduced the first touch screen monitor in 1983. These screens divide the display into rows and columns that correspond to x and y coordinates on the screen. This technology has been adapted to notebook computers in the form of touch-pad pointing devices, like the one illustrated in Figure 3.9.

Figure 3.9Figure 3.9 A touch pad.

This pointing device normally takes the place of the mouse as the pointing device in the system. The user controls the screen cursor by moving a finger across the pad surface. Small buttons are included near the pad to duplicate the action of the mouse buttons. With some touch pads, single and double button clicking can be simulated by tapping a finger on the pad.

The touch pad contains a gridwork of electric conductors that organize it in a row-and-column format, as depicted in Figure 3.10. When the user presses the touch pad, the protective layer over the grid flexes and causes the capacitance between the two grids within the pad to change. This produces a signal change that is detected by the touch-pad controller at one x-grid line and one y-grid line. The controller converts the signal generated between the two strips into an approximate x,y position on the video display.

Figure 3.10Figure 3.10 Inside a touch pad.

The human fingertip is broad and does not normally provide a fine enough pointing device to select precise points on the screen. Therefore, accurately locating a small item on the screen may be difficult due to the relative size of the fingertip. The touch-pad software designers have created drivers that take this possibility into account and compensate for it.

Touch pads are available as built-in units in some portables, whereas others are designed as add-ons to existing units. These units clip onto the body of the computer, or sit on a desktop, and plug into one of the system's serial ports, just as a mouse or trackball does.

Portable Drives

Smaller 2 1/2" form-factor hard drives, low-profile 3 1/2" floppy drives, and combination FDD/CD-ROM drives have been developed to address the portable computer market's need for compact devices. Older portables included one FDD and one HDD as standard equipment. Newer models tend to include a CD-ROM drive and an HDD as standard internal units.

More expensive notebook computers may substitute a DVD or CD-RW drive for the standard CD-ROM drive. Although internal DVD-RW drives can be installed in portable computers, they tend to be installed in only very high-end versions. On the other hand, external CD-RW and DVD-RW units are also widely used with portable computers. These drive units are described in greater detail later in this chapter. Figure 3.11 shows the placement of drives in a high-end notebook unit that includes one of each drive type.

Figure 3.11Figure 3.11 Portable disk drives.

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