Re: Seeing VERSIONINFO under Vista?

This was not an architectural restriction of the x86 family (which always had supported
32-bit addresses, however weirdly configured) but a pin limitation issue in the
implementaiton of the 286. However, that was not the real reason the 286 was
unsupportable. There were seriously deep architecture issues that could not be handled in
the 286, for example, its virtual memory map had problems, and in an era in which it was
still necessary to return to the BIOS frequently, it had been designed so that once it
entered virtual mode, it could not be reset to real mode (this was where the student paid
too much attention to the professor; we knew that having monotonic mutability was critical
for security, but it required that you have software that worked entirely in virtual
mode!). Read the BIOS code of a 286 to see how this was handled, but don't forget your
anti-nausea pill! What it did was have a line in one of the I/O ports that actually reset
the processor (I have this vague memory of port 60h or 61h). So when the processor reset,
it started up in real mode. Before tweaking this bit, a bit was written to the NVRAM to
say that this was a real-mode restart, so when it picked up the initail PC out of the BIOS
and branched off to handle it, there was code that checked this bit and then went off to
the virtual-to-real handler code to dispatch it.
joe

On Sun, 27 May 2007 15:18:42 +0100, Daniel James <wastebasket@xxxxxxxxxxxxxxxx> wrote:

In article news:<1t7c53d890rnss8mqsftpssgcbcm6nbm07@xxxxxxx>, Joseph M. Newcomer
wrote:
Win16 could not use more than 16MB of memory, since that was the maximum that
those boxes could support.

IIRC 16MB was the maximum a '286 could support. Win16 could use more memory when
run on a '386 (and in '386 mode it had much better memory management).

I was right.

Well, it /was/ a rather easy question.

Cheers,
Daniel.


Joseph M. Newcomer [MVP]
email: newcomer@xxxxxxxxxxxx
Web: http://www.flounder.com
MVP Tips: http://www.flounder.com/mvp_tips.htm
.

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