[BBC-Micro] OT PC architecture
rick at rs432.net
Thu Feb 18 01:38:28 GMT 2010
On 17/02/2010 01:31, Phill Harvey-Smith wrote:
> This is not to do with XMS/EMS, but more to do with the segmented
> addressing having a segment size of 64K.
True, but its all part'n'parcel. There were numerous programs that
needed more than 64K (but not that much more) that asked for a memory
manager to be loaded. I guess messing with memory management in extended
memory was easier than messing with memory models for the entire
Both have to be easier than expanded memory - that 380-oddK chunk
between the 640K that DOS 'sees' and the actual first 1Mb chunk; which
was nicely carved up into 64K pieces and paged in. Like BBC ROMs (to
make a really lame attempt at on-topicness ;^) ).
> and the main reason for that limitation has nothing to do with MSDOS,
However, had the IBM not used the x86 processors...
I wonder how Unixen worked pre-386? I know a lot of modern Linux-likes
won't run on earlier hardware, however the concept predates the
introduction of the 386. Was any sort of Unix released for earlier x86s?
I ask because it seemed in numerous walks of life, MS-DOS suffered from
the 64K/640K limitations (ever had to start a game from a special boot
disc as loading your regular device drivers only left half a megabyte
free?); so did these Unixen suffer similar problems or did they work
around it? [or not exist at all?]
> I dunno I seem to remember running Win95 on a 386 DX40 and it not being
> too bad by 1995 standards :)
Windows95 will RUN of a 386 (I got it started on my 386 co-pro) but it
isn't happy. If we ignore the emulated device support (Win98 and the
RiscPC 486 co-pro are not a good match, all sorts of weird stuff happens
like patterns and lines instead of icons), the physical side is largely
enhanced by having a better cache. Pipelining is difficult in the x86
because the instruction set is icky (but in its defence it dates back to
the '70s when the 6502/Z80 were all that), however the setup in the 486
In my room are five PCs (old one, mom's one, Aiko, Ayleigh, Azumi). 
In my room are four RISC OS machines (seven if you count the two Bush
boxes and the A7000 board. Plus my Zen. And the printer. And the PVR ...
ARM wins. Nerrr!
1 - plus 3 ST20s (satellite boxes), plus unknown processors in the
routers, *six* 6502-class (2 Beebs, 2 Elks, E01S, SJ Bridge). Heck, I
have more 6502s than x86!
2 - don't even try to count the number of processors in my room... to
give an example, the PVR TMS320DM320 contains an ARM core. Fair enough.
But the DSP is also a type of processor. As is the DCT unit. And the
video unit, but to mention the other hardware assist. The video
encoder/slicer contains a processor inside it. As does the audio chip.
There's probably a rudimentary processor inside the telly. Three DVD
players, several MP3 players... G*d almighty, it is starting to sound
like a cheap imitation of a William Gibson novel.
...I think it is safe to say the record player does NOT have a processor
in it. ;^)
Rick Murray, eeePC901 & ADSL WiFI'd into it, all ETLAs!
BBC B: DNFS, 2 x 5.25" floppies, EPROM prog, Acorn TTX
E01S FileStore, A3000/A5000/RiscPC/various PCs/blahblah...
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