origin of gates quote on 640k memory...

From: allisonp <allisonp_at_world.std.com>
Date: Tue Jul 11 19:28:53 2000

From: Neil Morrison <morrison_at_t-iii.com>


>FWIW, I believe his opinion was that 128K was enough. My recollection is
>that he wanted that amount to run Multiplan, and that is why he talked
>IBM into using the 8088 instead of the intended 8080 for the IBM PC.
>I believe this because Radio Shack sold add on cards for various Z80
>boxes they made so as to provide 128K for Multiplan (mainly).

Thats so far out left field that I can say there is little basis for it.
RS was not a significant vendor for memory cards or extensions.

As to the choice of 8088 vs 8080, nobrainer. Everyone knew by
1980 that while the z80 was a great cpu there were an emerging
class of apps that really needed 16 (or more) bit wide ALUs and
memory to perform well. Graphics was one of the emerging
apps and the other was programs like multiplan (math intensive).
These and others were the push for the 16bit world.

Additionally 8080 was quite passe` by 1980, 8085 maybe as it
was available as a 5mhz part (vs 8080 at 3!) and Z80 at 4mhz.
There was also Z8000 and other promised parts for the 16bit
world to come. I suspect 8088 won as it was quite easy to
interface and use.

Another point, Multiplan ran under CP/M with 48-60k of available memory
and most 8080 class (include z80) didn't have a MMU to manage more nor
did the OS (CPM2) have management. I have several systems that still
run multiplan (8080 and z80), they used overlays and on disk storage
very intensly to get around memory shortfalls. Additionally PC even
early
on were rift with code bloat (8080 lofted code tended to expand) and it
was
deemed a requirement to have more than 64k mostly due to the OS eating
most of it. At the time 256k was enough and it was felt (just like a few
years before when z80 64k was plenty) that was enough and if not 640k
would insure enough space. This is true also due to the segmented
addressing the 8088 used, it was still largely a 8/16bit cpu with 16bit
basic
addressing. Apps didn't grow well until the 286 memory style and more
aptly the 32bit 386 appeared.

An aside, non PC 8088/86 systems used to permit a full 1 MB of ram
via rom shadowing or added a mmu to extend beyond 1mb. So Billy boy
was really refering to those system that were promoting the full 1mb or
larger memory maps.

Allison
Received on Tue Jul 11 2000 - 19:28:53 BST