--- b e n w e l l s | headwerkx > one question though, according the codes listed, > some of those 3 chip SIMMs > are 4Mb modules - is that possible? Given the other > 1Mb and 4Mb SIMMs I've > seen have 8-9 chips on them, I'm wondering if I've > misinterpreted something.
The 8 or 9 chip SIMMs have each chip one bit "wide". 4 or 5 chip SIMMs have each chip two bits wide and 2 or 3 chip SIMMs have each chip four bits wide. A one meg 8 chip uses 128 kilobit x 1bit chips. A one meg 4 chip uses 128 kilobit x 2bit chips. A one meg 2 chip uses 128 kilobit x 4bit chips. The second chip is the equivalent of two of the first and the third is the equivalent of two of the second. With an odd number of chips, the SIMM uses the parity bit. With an even number it doesn't use parity. 9 chip parity SIMMs always have all the same chips. 5 and 3 chippers don't need the parity chip to be the same because that'd be wasted memory. Some parity SIMMs (other than 9chip) use a cheap little chip that always returns good parity data even if what's atually in the RAM isn't what it's supposed to be. Macs that use 30 or 72 pin SIMMs do not use parity so don't spend extra for parity SIMMs, unless you have the real rare US Government IIci that requires parity SIMMs. ===== http://www.junkscience.com "All the Junk that's fit to Debunk!" __________________________________________________ Do You Yahoo!? Yahoo! - Official partner of 2002 FIFA World Cup http://fifaworldcup.yahoo.com -- Vintage Macs is sponsored by <http://lowendmac.com/> and... Small Dog Electronics http://www.smalldog.com | Enter To Win A | -- Canon PowerShot Digital Cameras start at $299 | Free iBook! | Support Low End Mac <http://lowendmac.com/lists/support.html> Vintage Macs list info: <http://lowendmac.com/lists/vintagemacs.shtml> The FAQ: <http://macfaq.org/> Send list messages to: <mailto:[EMAIL PROTECTED]> To unsubscribe, email: <mailto:[EMAIL PROTECTED]> For digest mode, email: <mailto:[EMAIL PROTECTED]> Subscription questions: <mailto:[EMAIL PROTECTED]> Archive: <http://www.mail-archive.com/vintage.macs%40mail.maclaunch.com/> Using a Mac? Free email & more at Applelinks! http://www.applelinks.com
