Path: utzoo!utgpu!news-server.csri.toronto.edu!qucdn!leek Newsgroups: comp.sys.amiga.tech Subject: Re: Parity Checking / ECC RAM on the A3000 Organization: Queen's University at Kingston Date: Friday, 8 Jun 1990 13:34:47 EDT From: Message-ID: <90159.133447LEEK@QUCDN.BITNET> References: <756@bilver.UUCP> <1990May27.101258.24470@zorch.SF-Bay.ORG> <321@tlvx.UUCP> <1990May29.204550.27961@zorch.SF-Bay.ORG> <9 <3649@tymix.UUCP> In article <3649@tymix.UUCP>, pnelson@hobbes.uucp (Phil Nelson) says: >(if we had any) may be otherwise. If the Amiga had parity, it would easy to >get good data on the reliability of the memory IN THE BOX (not in some chip >test lab) and IN THE FIELD (not some clean, quiet final test area). > some stuff deleted... > >These are good points. I think it very likely that the memory system is not >the greatest cause of unreliability on the Amiga. Certainly not if you >include software bugs. This does not prove that parity checking is useless, >but that other measures are needed too. The order in which to take measures >to improve reliability is not determined exclusively by which is the worst >problem, it may be reasonable to start with a problem that is not the worst, >if a solution is easily implimented (memory parity checking, for example). > > I think the cost of ECC cannot be justified on the Amiga, unless for special >applications. The added cost of simple parity checking (not very great) might >easily by justified because it would help by allowing the early detection >and repair of machines with memory problems. It would be especially useful >for machines with flaky, intermittent memory. > > >|K. C. Lee > > >Phil Nelson . uunet!pyramid!oliveb!tymix!hobbes!pnelson . Voice:408-922-7508 > > If you thought prohibition was fun, you're gonna LOVE gun control. The problem with parity bit (vs ECC) is that it only do single bit error detection. If there are even # of bits having error, it doesn't know. The other thing have to do with design/economic/space. I can give you an example for myy particular set up. I have 4 meg of ram for my 18MHz 020. 32 chips of 256K*4 chips. For a parityy scheme, I would need 1 parity bit per byte. 680x0 is byte addressable so to do this properly is to have a parity for each 8 bit groups. Due to design and realibility problem, I would need a spearate chip for each 8 bit groups. Reasoning... Unless the 4 parity bits are squeezed into a 256k*4 chip and have a separate scheme for addressing that 4 parity bits and multiplex/demultiplex the parity bits to allow for byte/16-bit word/32-bit long word access. Sorry I can't do that without violating timing constraints unless faster chips are used instead of 60nS. Since the parity bits are accessed in different way - different gate delay which esult in slightly different timing. The hardware should also latch/synchronous the data bits before doing a checksum... All this mess to save space is not funny. To complicate things a bit more, I am running the 32 chips in a 4 bank page interleave mode - so i can't use 4 1meg*1 chip for the whole group either. That's 1 256K*1 chip per every 2 256K*4 chips. Excluding extra hardware ( and software exception handler..) That takes up 50% more space in my particular piece of memory board.. and all these trouble just to be able to warn me of a possible parity bit error ??? if I (or someone at C=) were to gone through the trouble to add parity, might as well go for ECC. A couple more bits per 32-bit word and you got Automatic Error detection and correction (and available with almost off the shelve parts eg. DRAM controller and ECC chip set from National Semiconductor) ECC/memory parity bit to boost realibility is like replacing all the wiring of a stereo (with cheap speakers) with solid silver strips - the sound certainly improves, but it might be more cost effective to replace the speakers. The speaker is a mechanical system and it generate more distortions than the electronic components. Most people would agree the above example. Now substitute the words below.. (stere= -> computer system, silver as wiring -> ECC, speakers -> programs, mechanical system -> software, distortion -> crashes) Sure if one have plenty of $$$ after upgrading the speakers to match the amp, one can spend $$$ on super conductors wire :) to hook up the speakers and may be a UPS for the stereo too. :) K. C. Lee ( I don't know much about stereo (only know the electronic side of it) , so don't flame me for using the above incorrectly as an example)