Roger Turk wrote:
>
> >From what I understand, the 640K limitation is *not* a hardware limitation,
> but BG's limitation, i.e., an MSDOS limitation. BG put the limitation in by
> loading device/video drivers, ROM BIOS, etc., in the top 284K of addressable
> memory, whether or not the bottom 640K was fully populated.
Actually it was IBM that put that barrier there. Although not actually 640k.
It could have been (and IS in most of my hardware) 704K.
The display memory was unfortunately located in the middle of useful space
instead of at (near) the bottom where the hardware could expand indefinitely
at the expensive of software space.
But at least then the software would have had ALL the contiguous memory from
the top of hardware (video memory, etc.) to the original 1Mb limit.
The bios is another problem. It also should have been placed at the bottom as
the first executeable code after the vectors and I/O. But the morons at Intel
placed the processor start address effectively at the top by causing reset to
set the Code Segment register to FFFFhex. IBM could have overcome this by
inverting some or all of the address lines, but chose not to complicate
programming any more than necessary.
Intel added the ability to re-map memory space to later processors.
The IBM PC as hardware is crap in more ways than one.
Of course, that is just MY opinion.
- Clarence Verge
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