The IBM Personal Computer 5150 was equiped with one of two revisions of its main system board throughout its production:
Up to March 1983, the 16-64KB board
From March 1983, the 64-256KB board A hand-made prototype IBM 5150 system board 16-64KB System Board 64-256KB System Board Common Specification
Intel 8088 CPU at 4.77MHzSocket for Intel 8087 FPU
5 ISA slots
4 banks of 9-bit (parity) RAM:
For 16-64KB board - using 16 kbit chips
For 64-256KB board - using 64 kbit chips
Physically 9" x 13"
DIN connectors for keyboard and cassette deck BIOS Revisions Configuration
The system configuration was set using two DIP switches.
Switch Block 1 This block is nearest the centre of the board.
Boot
Intel 8087
Sw1
Boot from
ON
ROM (Cassette) BASIC
OFF
Floppy Disk
Sw2
Intel 8087
ON
Not installed
OFF
Installed
Memory
Video
Floppy Drives
Sw3
Sw4
Banks Installed
ON
ON
One bank
OFF
ON
Two banks
ON
OFF
Three banks
OFF
OFF
Four banks
Sw5
Sw6
Video Type
ON
ON
No video or special (EGA, VGA)
OFF
ON
40 column CGA
ON
OFF
80 column CGA
OFF
OFF
MDA (or Hercules) Video
Sw7
Sw8
Floppy Drives
ON
ON
1 drive
OFF
ON
2 drives
ON
OFF
3 drives
OFF
OFF
4 drives
Switch Block 2 This block is nearest the CPU. Switches 1-5 define the total amount of memory installed (including that on expansion cards), and switchs 6-8 are always off.
Total RAM Installed
Sw1
Sw2
Sw3
Sw4
Sw5
16K
ON
ON
ON
ON
ON
32K
ON
ON
ON
ON
ON
48K
ON
ON
ON
ON
ON
64K
ON
ON
ON
ON
ON
96K
OFF
ON
ON
ON
ON
128K
ON
OFF
ON
ON
ON
160K
OFF
OFF
ON
ON
ON
192K
ON
ON
OFF
ON
ON
224K
OFF
ON
OFF
ON
ON
256K
ON
OFF
OFF
ON
ON
288K
OFF
OFF
OFF
ON
ON
320K
ON
ON
ON
OFF
ON
352K
OFF
ON
ON
OFF
ON
384K
ON
OFF
ON
OFF
ON
416K
OFF
OFF
ON
OFF
ON
448K
ON
ON
OFF
OFF
ON
480K
OFF
ON
OFF
OFF
ON
512K
ON
OFF
OFF
OFF
ON
544K
OFF
OFF
OFF
OFF
ON
576K
ON
ON
ON
ON
OFF
608K
OFF
ON
ON
ON
OFF
640K
ON
OFF
ON
ON
OFF
See Also 