Hardware Architectures and I/O (was: Re: Jargon file...) **FLAME!!**

[Robert E. Seastrom]

wcs at cbnewsh.att.com (Bill Stewart 908-949-0705 erebus.att.com!wcs) writes:
>rs at eddie.mit.edu (Robert E. Seastrom) writes:
>> RS-6000s also have an annoying tendency to "lock
>> up" for a few seconds (5 < x < 15) and then return to normal - I'm
>> told that this is normal and due to paging activity.  
>
>AAARGH!  My VAX 11/780 used to behave in this pathological manner,
>which is much more annoying when you have a dozen people doing vi
>than one person.  We were trying to do a 12MB process on a 4MB VAX,
>and had used 4.1BSD for a while.  We got about the third copy of
>VAX Paging SVR2 to leave Summit - it wasn't a beta copy (which
>implies support), it was just a favor (thanks, Doris!)

Well, I was talking about running one X server and one Emacs in a
machine with 16 MB of memory.  I wasn't abusing the poor thing with a
process that was 3 times as big as my physical memory (probably 4
times as big as available memory once you take out space for the
kernel).

>VAX OS's were somewhat flaky then because of the brain-damaged DEC
>UDA-50 disk controllers and suicidal-to-install DEC patchware,
>and our machine had a giMongous amount of memory compared to the
>average VAX or 3B2 of its day.

What, you were paging to a Unibus disk?  UBAs weren't designed to do
heavy-duty I/O.  You'd probably have been much better off with a
Massbus disk (find an RM03, hang it off a massbus adaptor of its own,
and dedicate the whole disk to swap).  I'm not saying that you had any
choice (you probably had one of the early memory controllers that
would only support 4 MB maximum anyway), but poor performance is to be
expected on a system which you've seriously overloaded.  I should
think that a workstation that is billed as being blazingly fast would
be able to handle running X and Emacs at the same time.

                                        ---Rob




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