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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.micro
Subject: Re: 386 Family Products
Message-ID: <6246@utzoo.UUCP>
Date: Fri, 20-Dec-85 17:17:20 EST
Article-I.D.: utzoo.6246
Posted: Fri Dec 20 17:17:20 1985
Date-Received: Fri, 20-Dec-85 17:17:20 EST
References: <129@intelca> <4400130@uiucdcsb> <6185@utzoo.UUCP>
Organization: U of Toronto Zoology
Lines: 37

> On the 386, "small model" (which of course does not exist per se) is
> 4 Gigabytes.

Quite true, but irrelevant to the point I was making:  that the 386's
segments are largely useless, and do not constitute a useful feature.
The *reason* they are useless is indeed that "small model" on the 386
is big enough for most needs.  This is a major improvement on the situation
for the earlier *86's, where the segments were just as brain-damaged but
could not be avoided because "small model" was too small.

> He says that the segmentation registers give nothing and wont be used
> by anyone.
> 
> Fine, I'm willing to accept that as the basis of a discussion.  So
> now instead of using those features as an invalid argument *against*
> the 386, lets ignore them and look at the rest of the chip (and read
> the data sheets, so that we can discuss *facts*).

I wasn't using them as an argument *against* the 386, I was attempting to
refute an article of yours which said quite explicitly (a) the segments
are a neat feature, and (b) they provide added [implied to be useful]
functionality over the MMUs on things like the 68020.  Which is wrong, as
you have just admitted.  Now that the size of the linear addresses is large
enough, the ability to segment your address space is essentially useless,
and can properly be ignored except in unusual cases.  About time.

The only way in which the segments are an argument *against* the 386 is
that they take up silicon which could have been better used for other
things.  I do not see this as a serious defect; most of the other CPUs
around have at least one equally-useless "feature".  (The MOVEP instruction
was of some interest on the 68000 but is as useful as feet on a fish for
the 68020; the 32032 string instructions run slower than tight loops that
do the same thing; the VAX is loaded with useless gingerbread; even the
fairly-clean PDP11 has the brain-dead MARK instruction.)
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry