There seems to be a memory count bug regarding the AMI 386, AMI 486 and AMI WinBIOS 486.
PCem currently tolerates a limit of 256 MB of memory. However, if you manually edit the pcem.cfg file and change the value to mem_size = 641 or higher, the AMI 386, AMI 486 and AMI WinBIOS 486 ROMs WILL NOT be able to recognise more than 655,296 KB of tested system memory (640 MB - 64 KB) and hang with a blinking cursor below the last good tested memory count.
By manually editing the mem_size past the 256 MB limit, a 386DX or 486 based emulated computer on PCem will be able to tolerate up to 640 MB of memory at a absolute maximum and that is it. Anything higher than 640 MB and the BIOSes that I mentioned will lock up. If you manually edit the amount of memory to 1024 or higher, PCem will crash!
I suspect that this is often the case, because large memory sizes on these old BIOSes were not available at the time when they were released and I don't think that this is fixable. The 640 MB memory count bug might have been fixed in later Pentium MMX-based AMI BIOSes I believe.
Edit: In AMI 386 and AMI 486 bases BIOSes, if you set the mem_size value between 65 to 640, the BIOS will count all of the available tested RAM, but up to 64,512 KB (63 MB) of extended RAM will be usable due to the chipset limitation: http://forums.bannister.org/ubbthreads.php?ub … at&Number=92856
It seems to me that the 64 MB limit in these BIOSes is a BIOS limit in INT 15h FUNC 88h. The 64 MB bug was eliminated in the AMI WinBIOS 486 and up.