Re: AltairZ80 simulator updated

Remember that the original IBM-PC had basic in ROM. Plus BIOS. Plus hardware memory mapped I/O (including devices that were then being designed but that would not come to market for another 2 years, like the EGA and PGA video cards).


dott.Piergiorgio wrote:
Howard Harte ha scritto:
On Jul 28, 2:10 pm, "dott.Piergiorgio"
<dott.PiergiorgioNI...@xxxxxxxxxxxxxxxxxxxx> wrote:
Peter Schorn ha scritto:

The AltairZ80 simulator has been updated and is available for download
athttp://www.schorn.ch/cpm/intro.html
New:
- Various new devices (courtesy of Howard M. Harte)
- New operating systems to play with (courtesy of Howard M. Harte)
* 86-DOS by Seattle Computer Products
This 86-DOS is *really* interesting, esp. the chckdsk's last line of
output, whose reveal that there wasn't technical limitations for the use
of the full 8086/88 moby, gate$ and the IBM engineers has really huge
blames.

Best regards from Italy,
Dott. Piergiorgio.

Try MS-DOS 1.25. You'll find more evidence that the 640k barrier is
not a limitation of MS-DOS, but rather a limitation of the PC
hardware. Of course, the IBM had to put memory-mapped I/O somewhere,
and 10x CP/M-80 RAM probably seemed reasonable at the time.

I can agree on this, but... why starting with A bank and not, say, D or E bank ? ;)

Until MCGA video memory & graphic register can be inside an entire 64K bank, and AFAICT the three XT bios (system, HD controller and graphic card) can fit inside an entire 64K bank, if one known how to do things in 8086 asm.


It also looks like there is a bug in chkdsk, but Tim Paterson probably
didn't have a meg of RAM to test with.

hmmm... indeed the .pdf of Paterson's ad for his 8086 cards show a 16 Kb RAM card; and also a quick glance of the manuals seems to show no trace of memory models other than .COM/tiny; I think that the effective capability of handling large binary of 86-dos can be (theorically) tested with a code whose has a sequence nearby 64K of NOPs and a brief routine at the end of bank whose print the bank done. I guess can be easily done with a good macro assy.

For now, I'll try to give SIMH SET CPU MEMORY=768k (if works, the documentation isn't clear on this command...) and look what chkdsk outputs.

But I agree that this "0 bytes total system RAM" seems a clear evidence of some bug or nonimplemented routine.

Thanks for your reply and informations !

Best regards from Italy,
Dott. Piergiorgio.
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