Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!amdahl!nsc!glennw
From: glennw@nsc.nsc.com (Glenn Weinberg)
Newsgroups: comp.arch
Subject: Re: Today's dumb question...
Message-ID: <5056@nsc.nsc.com>
Date: 10 May 88 18:07:24 GMT
References: <503@xios.XIOS.UUCP> <2676@pdn.UUCP> <674@cernvax.UUCP>
Reply-To: glennw@nsc.UUCP (Glenn Weinberg)
Organization: National Semiconductor, Sunnyvale
Lines: 46
Summary: Yes, I agree, it was a dumb question


In article <674@cernvax.UUCP> hjm@cernvax.UUCP (Hubert Matthews) writes:
>
>     To summarise all of this in a few points:
>
>	- virtual memory is useful only when an application won't fit in
>	  physical memory.  But memory is cheap, so with lots of Mbytes
>	  who needs it, especially if the program is written well.
>
>	- multi-user machines are too complicated to be both fast and simple.
>
>	- shared-memory is not necessary; it's a software issue that shouldn't
>	  be solved in hardware.
>
>     For example, 10 MIPS of computation with 4 MB of ECC RAM can be placed on
>a single 4" x 6" Eurocard.  Add multi-user support, virtual memory or multiple
>CPUs and the board looks like a football pitch in comparison.  Guess which is
>cheaper as well!
>

I beg your pardon?  There are VME boards available today that contain a
NS32532 (a 10 MIP processor) with 64KB of cache and 4MB of memory, support
Unix* System V Release 3 (which is a multi-user system, of course), virtual
memory, and can be combined into a multiprocessor configuration.  I do
believe that a double-height VME board is slightly smaller than a "football
pitch" (the actual dimensions are 6" x 9").  Furthermore, put the board
into a VME chassis with a SCSI controller, a 5-1/4" hard disk, a cartridge
tape and an Ethernet board and you have one hell of a system in a box that's
about the size of the proverbial breadbox for less than $20,000.

Sure, you can argue that supporting multi-user environments and virtual
memory costs you something, but there are very, very few real-world
situations in which you have no need to interact with other systems and
people.  You simply can't do that unless you have a system which both allows
you to have that interaction and protects you from the (un)intentional
dangers of the outside world.  Not to mention the other benefits you
get from a multi-user, multi-tasking operating system such as Unix.

In summary, unless your system is used only as a dedicated processor
that does no interaction with human beings, the advantages of a multi-user
virtual memory (or at least memory-protected) environment significantly
make up for any increase in cost or board space.

-- 
Glenn Weinberg					Email: glennw@nsc.nsc.com
National Semiconductor Corporation		Phone: (408) 721-8102