16 Aug
2024
16 Aug
'24
6:42 p.m.
On Fri, 16 Aug 2024, Peter Corlett via cctalk wrote:
It's also worth noting that the PC memory space is
very much *not* divided
into fixed 64KiB segments (and ISTR it was originally a 512/512 split).
Segment registers have 16-byte granularity and a segment can straddle a
64kiB boundary just fine. This is used to some effect on the 286 to gain an
extra 65520 bytes beyond the 1MiB boundary in real mode.
A segment can, indeed, straddle a physical 64KiB boundary.
5150 disk IO had problems if the DMA buffer straddled a
physical 64KiB boundary (Int13h return code 9)
Not hard to work around; just move the buffer
https://stackoverflow.com/questions/58564895/problem-with-bios-int-13h-read…
--
Grumpy Ol' Fred cisin(a)xenosoft.com