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From: pshuang@ATHENA.MIT.EDU
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Unix on 486 Machines
Message-ID: <9106110417.AA06408@w20-575-117.MIT.EDU>
Date: 11 Jun 91 04:17:15 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 44

In article <44390@netnews.upenn.edu> jer@pender.ee.upenn.edu (Joel
Ratsaby) writes:

 > Is the architecture of 486 ISA  (Not EISA) machine fit for
 > Unix or is the 32 bit capability of the 486 is masked by the
 > ISA architecture ?
 > 
 > If I use DOS 5.0 can I do multitasking (without Windows package)
 > and is the 32 bit capability of the 486 masked by DOS ?

486 ISA machines are quite fit for UNIX, as are 386 ISA machines.  You
won't get the same kind of snappy performance as the mid to high-end
workstations, but it will be acceptable, especially if you spend a fair
amount of money to insure that the machine is equipped with a very fast
and large disk drive and a speedy display adaptor board which can
support a high resolution screen and possibly has a graphics coprocessor
on it.  The bus does not seem to be as huge an issue as IBM would have
had you believe with their push for MicroChannel architecture, according
to PC Magazine tests about a year back, when they concluded that for
most setups and users and applications, ISA vs. EISA vs. MicroChannel
made little difference to real-world throughput.  In any case, ISA's
16-bit bottleneck applies only to I/O and does not affect the 32-bit
processing speed of the i486 CPU, unless you are supplying memory via a
expansion board on the bus, which would be plain silly.

DOS 5.0 does not provide multitasking, but only task switching, and
according to Bill Gates at the BCS meeting tonight, it never will.
Since DOS runs the i386 and i486 chips in real mode (for compatibility
with the 8088 chip), in a sense their 32-bit capabilities are masked and
performance reduced, and in a sense they aren't.  To a small extent,
performance in real mode is enhanced because memory accesses are
slightly slower in protected mode (because it does take a little time to
provide the memory protection, after all).  However, because DOS
software rarely takes advantage of the "newly" introduced 32-bit
instructions in these chips or their ability to access directly more
memory, often they don't take full advantage of the full capabilities of
the new chips.  Several very demanding applications (AutoCAD, Paradox)
exist in both DOS versions (compatible with any machine from 8088 and
up) and in special 386 versions.  Running them on the same machine, I
believe you can see a considerable speed-up, maybe on the order of 100%,
of the 386-specific version over the general version.

Singing off,
UNIX:/etc/ping instantiated (Ping Huang).