Parent

IBM 32KB Memory Expansion Option  -  Switches


Switches 1 to 5 control the starting address of the RAM.

Starting address	Switch settings	Comment
32 KB	1=on, 2=on, 3=on, 4=on, 5=off
64 KB	1=on, 2=on, 3=on, 4=off, 5=on
96 KB	1=on, 2=on, 3=on, 4=off, 5=off
128 KB	1=on, 2=on, 3=off, 4=on, 5=on
160 KB	1=on, 2=on, 3=off, 4=on, 5=off
192 KB	1=on, 2=on, 3=off, 4=off, 5=on
224 KB	1=on, 2=on, 3=off, 4=off, 5=off
256 KB	1=on, 2=off, 3=on, 4=on, 5=on
288 KB	1=on, 2=off, 3=on, 4=on, 5=off
320 KB	1=on, 2=off, 3=on, 4=off, 5=on
352 KB	1=on, 2=off, 3=on, 4=off, 5=off
384 KB	1=on, 2=off, 3=off, 4=on, 5=on
416 KB	1=on, 2=off, 3=off, 4=on, 5=off
448 KB	1=on, 2=off, 3=off, 4=off, 5=on
480 KB	1=on, 2=off, 3=off, 4=off, 5=off
512 KB	1=off, 2=on, 3=on, 4=on, 5=on
544 KB	1=off, 2=on, 3=on, 4=on, 5=off
576 KB	1=off, 2=on, 3=on, 4=off, 5=on
608 KB	1=off, 2=on, 3=on, 4=off, 5=off

How were those calculated ?
It's an inverted binary sequence based on the fact that switches 1 to 5 monitor address lines A19 to A15 respectively.

1. Divide by 32 KB
2. Convert result to binary
3. Prefix binary with additional zeroes to make 5 digits
4. Invert it

Example: 192 KB --> 6 --> 110 binary --> 00110 --> 11001 (on/on/off/off/on)