XPost: comp.os.ms-windows.misc, alt.windows7.general, microsoft.
ublic.windowsxp.general
From: admin@127.0.0.1
On Fri, 29 Dec 2023 11:31:31 -0500
Tim Slattery wrote:
> Steve Hayes wrote:
>
>
> >I think early programs running on IBM PC DOS or MS DOS were 8-bit,
> >running on 8088 processors. The 286 and 386 ones were 16-bit.
>
> Not so. The original IBM-PCs were 16-bit machines. They used a kludge
> to implement a 20-bit address space, allowing access to one megabyte
> of RAM. You may remember that 340KB of that was reserved for the
> operating system, leaving 640KB for user program.
No to that 2nd sentence; the upper address space was used for direct
addressing the screen buffer (0xB000 for mono, 0xB800 for text/CGA, 0xA000+
for higher modes)), extension card interfaces, and ROM (E000 & F000) - I
suppose you could argue that a ROM BASIC is an operating system, but I
wouldn't accept that. Certainly user programs were only allowed a max
memory footprint of 640k - in practice much less due to DOS overhead.
> 1970's vintage machines, such as Cromemco, Zylog, etc, etc, were 8
> bits. I'm a bit foggy on their addressing schemes, but at least some
> of them could switch between banks of 64KB each.
>
> The 80286 was basically 16-bits, but implemented "protected mode"
> which allowed access to 16MB. Windows programers (if they're old
> enough) may remember using "GlobalAlloc" and "GlobalFree" calls. Those
> manipulated the Global Allocation Table, a 80286 protected mode
> hardware kludge that kept track of all that RAM.
>
> The 80386 was Intel's first true 32-bit machine. Windows 3.0 386
> version ran in 16-bit 80286 protected mode though. It took a while for
> Windows to catch up with 32-bit processors.
>
> --
> Tim Slattery
> timslattery utexas edu
--
Bah, and indeed Humbug.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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