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I 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 th
by hakfoo 3y ago
I 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.