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

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. 1-12