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> I wonder how this will affect quirks such as A20, ... All oversights and mistakes made by Intel over the years Well, the A20 gate was actually IBM's creation
by pwg 3y ago
> I wonder how this will affect quirks such as A20, ... All oversights and mistakes made by Intel over the years
Well, the A20 gate was actually IBM's creation, in order to make the PC-AT system compatible with running real-mode DOS programs.
Intel simply, later, incorporated it into the CPU because it was already part of the PC architecture (and had been for years) at that time.
Now, one could argue Intel had no business incorporating it into the x86 ISA, but it wasn't ever their oversight, they were just reacting to the reality of the systems in which the vast majority of their CPU's were used.
- hakfoo 3y agoI thought it was a 286 errata-- where the address didn't wrap around correctly in real mode. The "fix" was IBM repurposing the keyboard controller to fix up the behaviour on A20.
- mlyle 3y agoNot "errata". 286 had more address space, so above 1MB didn't wrap around (by design). But this differed from 8086.
- hakfoo 3y agoI thought the idea was that in real mode it should be have like a faster 8086, and exposing memory beyond 1Mb breaks the illusion.
- mlyle 3y agoIt does break the illusion. At the same time, it allowed another ~64k of memory, which was important. DOS eventually sat up there in the non-wrapped memory. So, feature or bug? Heh.