Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!pacific.mps.ohio-state.edu!linac!mp.cs.niu.edu!bennett From: bennett@mp.cs.niu.edu (Scott Bennett) Newsgroups: comp.sys.next Subject: Re: Non-parity SIMS Message-ID: <1991Mar11.045612.1764@mp.cs.niu.edu> Date: 11 Mar 91 04:56:12 GMT References: <23938@hydra.gatech.EDU> Organization: Northern Illinois University Lines: 43 In article <23938@hydra.gatech.EDU> gt5223b@prism.gatech.EDU (Doug Berkland) writes: >What are non-parity SIMS? Non-parity SIMMs have only eight chips, i.e. eight bits per byte. Parity SIMMs have a ninth chip (nine bits per byte) that allows the surrounding hardware to detect, and in many systems correct, single-bit errors. Some systems are also able to detect, but not correct, double- bit errors. Another answer to your question is that it depends on what you're using the memory for. If you're using it for any purpose where relia- bility is important (e.g. numerical applications, an operating system whose integrity you care about, etc.), then the answer is that non- parity SIMMs are worthless. That's why computer manufacturers abandoned non-parity memory by the 1950's. On the other hand, if reliability is not important to you, then non-parity SIMMs represent perhaps a $4-$10/SIMM savings on a one-time basis for 1Mbx8 SIMMs (as opposed to 1Mbx9, i.e. w/parity bits) or perhaps $15-$35/SIMM for 4Mbx8's vs. 4Mbx9's. The new, 68040-based NeXTs can be configured either w/parity or w/o parity, as you prefer. I am told, however, that NeXT has screwed up the hardware design in those machines in a way that causes the use of parity memory to introduce wait states. The old, 68030-based NeXTs cannot use parity memory. >Thanks in advance. >-- >Doug Berkland Internet: gt5223b@hydra.gatech.edu Phone: (404)676-9068 >uucp: ...!{decvax,hplabs,ncar,purdue,rutgers}!gatech!prism!gt5223b >Georgia Institute of Technology, Atlanta GA 30332 <> > "If I don't have it, how do I know I don't want it?" --me Scott Bennett, Comm. ASMELG, CFIAG Systems Programming Northern Illinois University DeKalb, Illinois 60115 ********************************************************************** * Internet: bennett@cs.niu.edu * * BITNET: A01SJB1@NIU * *--------------------------------------------------------------------* * "The good news is that Saddam Hussein will be tried for war * * crimes. The bad news is that the case will be heard by the * * Senate Ethics Committee."--quoted in _The_Wall_Street_Journal_ * **********************************************************************