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