Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!bionet!ames!amdahl!JUTS!duts!kls30 From: kls30@duts.ccc.amdahl.com (Kent L Shephard) Newsgroups: comp.sys.next Subject: Re: memory (was: slab vs. cube and $$) Message-ID: Date: 6 Dec 90 16:08:07 GMT References: <1990Nov28.191405.25218@mp.cs.niu.edu> <12081@life.ai.mit.edu> <1990Nov29.161041.15775@magnus.ircc.ohio-state.edu> <27560D70.24700@maccs.dcss.mcmaster.ca> <18042@hydra.gatech.EDU> <1567@ulowell.ulowell.edu> Sender: netnews@ccc.amdahl.com Reply-To: kls30@DUTS.ccc.amdahl.com (Kent L. Shephard) Distribution: na Organization: Amdahl Corporation, Sunnyvale CA Lines: 39 In article <1567@ulowell.ulowell.edu> koverber@hawk.ulowell.edu (Kurt Overberg) writes: > > It is useful as far as error detection and correction. If you > have a memory error, parity ram will try to correct the error at ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Not true parity and error correction are totally different. 1 bit parity (basically an XOR of all the bits) like on IBM PCs, optional on Macs, and I suppose the NeXT will only detect a bit flipping if 2 bit flip 1-->0 and 0--> you don't get a parity error with one bit detection. Error correction is a different animal entirely. It requires more bits, more complicated logic etc. > much as possible. I have heard (no proof) that parity ram is > required on all hospital (medical) computers, but then again, this > is not substantiated. The actual helpfulness of parity ram is, > however, questionable. ~~~~~~~~~~~~~ Depends on if you halt the system, or issue an interrupt that has a sevice routine that asks if you would like to continue or not. If your doing a critical calc. that has to be right you don't want a bit flipping in the MSB, but if your doing word processing 1 bit in 1 character isn't going to make a bit of diff. if you go back and proofread. > >+--------------------------+--------------------------------------------------+ >| This space | "There once was a time when ( ACK ! ) | >| for rent | my life was so wonderful..." (_______) | >| | "Then they sent me away, taught me o | >|#include | how to be logical...sensible, o | >|--------------------------| rational, a vegetable..." _ /| | >|koverber@hawk.ulowell.edu | -Supertramp \`o.O' | >+--------------------------+--------------------------------------------------+ -- /* -The opinions expressed are my own, not my employers. */ /* For I can only express my own opinions. */ /* */ /* Kent L. Shephard : email - kls30@DUTS.ccc.amdahl.com */