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O.K. Not clear from what was described. So the BIOS keeps the memory size in CMOS and prompts when it changes?
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Hmmm ... not on the CP/M machines which I used from time to time. They used RS-232 connected terminals, and did not have a way to tell whether the keyboard was present. Perhaps some of the single-board CP/M machines with a built-in terminal, however.
And -- my Altair 680b did not even *need* a terminal. It could be jumpered to accept program loading and starting from the front panel switches. (The only way to load and run a program when I first got it. :-)
And the Sun workstations, which did have keyboards would simply detect the missing keyboard, and switch over to use the first serial port as a terminal -- expecting a terminal to be connected to it. It was a common way to set up servers, which did not need a graphics screen or keyboard -- just a terminal to get them started and/or to diagnostics. Leave out the keyboard or the graphics card (called a "framebuffer") to switch to a serial terminal as the console.
Enjoy, DoN.