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[HACK] 1 MB RAM PCem machine configuration

Posted: Mon 27 Jun, 2016 12:25 am
by ppgrainbow
I looked at the configuration file for the emulated IBM PS/1 Model 2011 machine (ibmps1_2011.cfg) as a example and I found something really interesting.

It is possible to run a emulated machine with 1 MB of usable RAM, only if you manually change the mem_size varlable to the following:

mem_size = 1408

This hack makes is possible to use the 640 KB of base memory, plus 384 KB of extended memory. This is required if you want to run Windows 3.0 or Windows 3.1 in Standard Mode. If the variable reads mem_size = 1024, the remaining 384 KB will be used as upper memory and will not be able to the machine, leaving 640 KB usable.

As a consequence, with only 640 KB of RAM on a emulated 286 machine or higher:

1. You will not be able to use HIMEM.SYS.
2. You will only be able to run Windows 3.0 in Real Mode.
3. You will not be able to run Windows 3.1 at all.

I'm always wondering if it is now even possible to run a emulated 286-based machine with less than 1 MB of memory now. When the IBM AT came out in 1984, it only came with 256 KB of usable RAM and there wasn't even any upper memory available at all.