Re: AltairZ80 simulator updated

Barry Watzman wrote:
The 640k limitation was ENTIRELY in the hardware. The Heath/Zenith Z-100 allowed 768k of user RAM (it's video and bios used the last 256k), and it was running the same OS as the PC.


Dennis Boone wrote:

> 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.

The 640 barrier was largely illusory anyway. Basic memory management
support in DOS had most of what it needed to support 1 MB, as evidenced
by the high memory support of later years.

The real mind blower is the short-sightedness of a 1 MB limit. The cause
of that one is the size of a paragraph, the basic unit of the segment
register.

De

** Posted from http://www.teranews.com **




The 8088 had a 20 bit address bus = 1 meg.
.

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