IBM Personal Computer (5150): System Unit, Keyboard and Display (IBM Technical Reference, 1981)

On the system board, fit the Intel 8088 processor. It runs at 4.77 MHz, taken from a 14.31818 MHz crystal divided by 3; divided by 4, the same crystal gives the 3.58 MHz colour-burst signal for colour TVs. Fit its support chips: the 8237A-5 DMA controller, 8259A interrupt controller, 8253-5 timer and 8255A-5 peripheral interface. Add the ROM holding the BIOS, the read/write memory, the speaker circuit, five expansion slots, and 5-pin DIN sockets for the keyboard and a cassette recorder. The 8088 runs in maximum mode, so a coprocessor can be added later. Set switch SW1 to tell the machine what it has: whether to start from a 5-1/4 inch diskette drive, how much read/write memory is on the board, which display adapter is fitted, and how many diskette drives there are. Not given here: the board layout.

Screw the system board into the system-unit chassis. Fit the power supply at the right rear; its housing supports the rear panel and its fan cools the whole machine. It is rated for 63.5 W continuous, from a fused 120 V or 220/240 V input. Its four protected outputs are +5 V at 7 A, +12 V at 2 A, -5 V at 0.3 A and -12 V at 0.25 A, bussed to all five slots. It also has a power-good signal, a switched mains socket for the monochrome display and two drive power plugs. Not given: the chassis metal and sizes.

Fit up to two 5-1/4 inch diskette drives, each powered from its own plug on the supply. Only one drive runs at a time. Plug a diskette drive adapter and a display adapter (monochrome or colour/graphics) into expansion slots, and cable the drives to their adapter. Not given here: the adapter cards and cables, which IBM describes in its separate Options and Adapters volumes.

Plug in the keyboard: 83 keys, with the typewriter keys in the middle, 10 function keys on the left and a 15-key pad on the right. It sends scan codes, not letters, so the software decides what each key does. Connect the display to its adapter and to the switched socket. Switch on: the power-on self-test in the BIOS checks the machine, sets up its interrupt vectors, and looks for extra ROM on the adapter cards. The bootstrap loader then starts the operating system from a diskette.