Date : Thu, 18 Feb 2010 02:38:28 +0100
From : rick@... (Rick Murray)
Subject: OT PC architecture
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
application?
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
improved things.
In my room are five PCs (old one, mom's one, Aiko, Ayleigh, Azumi). [1]
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 [2]...
ARM wins. Nerrr!
;-)
Best wishes,
Rick.
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...