THE MICROCOMPUTER

In this section, we will examine the microcomputer with its individual hardware components. We will examine it from the inside. You will see how the components work and how they interface and interconnect with one another.

There will come a time when you maybe required to replace or add a board in a computer to upgrade or expand the capabilities of the system. A few examples are as follows:

You may need to install an expanded memory board to increase the amount of RAM to accommodate larger applications.

You may have to replace the enhanced graphics adapter (EGA) board with an video graphics array (VGA) board to upgrade the graphics capabilities of your system.

You may need to install a communications board.

You may receive a new software release that requires the presence (or absence) of certain boards to function properly. You do not want to find out too late that your software is incompatible with your hardware. You might have to answer questions such as the following: Will the graphics software the user wants to order work with the graphics board currently installed in the system? Does the user's system have sufficient room to accommodate another hard disk drive? A diagnostics routine may indicate that the disk controller board needs to be replaced, and so on, and so on. For reasons such as these, you will need to know a lot more about microccomputers (both inside and out) if you are to be effective and able to help others in your work environment.

The Computer or System Unit

The computer or system unit is the main part or heart of the total microcomputer system. Inside this unit all data is processed, arithmetic and logic functions are performed, and control is maintained for the system. If you were to remove the outer cover from this unit (figure 1-8), you would see a power supply and as many

Figure 1-8.\A microcomputer system unit with the cover removed.

as two floppy disk drives and two hard disk drives or any combination thereof, depending upon the particular configuration of your system. You would also see several boards (also referred to as cards). Some boards are used to control the peripheral devices of the system, while other boards work in conjunction with the microprocessor that is located on the system or motherboard itself. These boards provide the flexibility to add a variety of capabilities to a basic system. Certain boards are required, such as the system board that contains the main microprocessor(s). Others you might add to control a light pen or mouse device, or to handle a communications interface.

Looking inside the computer system unit (figure 1-8), you will notice there are 5 available slots for board insertion. These various boards are plugged into what is called the motherboard. The motherboard is a printed circuit board that transmits the power and electronic signals between the other boards and peripheral devices. It is mounted to the bottom of the chassis of the computer, as shown in figure 1-9. Memory chips, on the newer micros, called single in-line memory modules (SIMMs), are located on the motherboard in a group of 4 or 8 slots. In older micros the memory chips are located on a memory expansion board. Most microcomputers also have a lithium battery installed on the motherboard. It provides power to the real-time clock when the system is turned off. The life expectancy of this battery is 3 to 5 years. Other boards you are likely to see in a typical microcomputer are the disk controller board, SCSI adapter board, and video display board (figure 1-9). We will take a look at each.

SLOT A\SCSI ADAPTER BOARD.\ The small computer systems interface (SCSI) adapter board is used to control peripheral equipment, such as a CD-ROM drive.

SLOTS B, D, E, F, AND H.\ Slots B, D, E, F, and H on this particular micro are reserved for future use.

SLOT C\DISK CONTROLLER BOARD.\

Most disk controller boards are capable of supporting two internal hard disk drives, two internal floppy drives, and one external magnetic tape drive for tape backup.

SLOT G-VIDEO DISPLAY BOARD.\ The video display board includes graphics memory chips to provide the system with graphics capabilities. Most micros come from the factory set for VGA (video graphics array) settings.

By now, you should have a pretty good idea of what you can expect to see inside the system unit in the way of microcomputer boards. Before installing any internal components within the system unit, you must first carefully remove the outer cover. Be sure you are authorized to make such changes before removing the cover. However, before you go looking for a screwdriver, read the owner's manual very carefully, paying particular attention to the section on cover removal and the steps to follow. For example, the owner's manual might say: "Once all cabinet screws have been removed, raise the cover, keeping it as high as

Figure 1-9.\Boards within the microcomputer system unit and their locations.

possible while pulling it forward for removal." This action ensures that none of the internal wires, cables, or connectors are accidentally pulled loose and avoids possible damage to the components already installed inside the system unit.

So that you will have a better understanding and appreciation for this microcomputer, we will take a closer look at microprocessor chips and see how they differ from one another. We will also examine what all this means to you from a communications specialist's standpoint.