[CUBE] ECC when it come to memory

[Joost van de Griek]

On 2003-08-18 18:13, Robert W. Bumala wrote:

> I believe you're thinking of EDAC (Error Detection and Correction).  We
> use that for RAM that's exposed to a high radiation environment, such as
> space.  Normal EEC RAM just has a parity bit, and most IBM Wintel
> machines use it.  Way back when about 5 BM (Before Macintosh), IBM
> decided that the DRAM memory needed a parity bit to detect errors.  It
> didn't fix errors, just crashed the machine with a parity error.  Apple
> figured that if the memory was bad it'd crash all by itself, they didn't
> need a parity bit.  This is why when you buy memory for a Mac, it has a
> missing chip, that's the parity bit.  It's fairly useless, but wintel
> machines still use it for some odd reason.  People in the IBM-like world
> jump through all kinds of hurdles to maintain compatibility with an old
> obsolete architecture.  That's why they lived with the dreaded 1
> megabyte limit for so long.

Well, that's stretching things a bit...

First off, parity SIMMs detect data errors, not memory errors. Secondly,
while a data error in application code may cause a machine to crash, hang,
or behave erratically, a data error in actual data will cause it to run just
fine, but with errors in your results (garbage in, garbage out). This is the
main reason that many professional computer hardware manufacturers use
parity memory, such as IBM, SGI and Sun.

I'm sure we can all appreciate the inclusion of data integrity checking
mechanisms in the machines that control nuclear power plants and weapons
systems, right?

,xtG
.tsooJ
-- 
Early to rise,
Early to bed,
Makes a man healthy,
But socially dead.
-- 
Joost van de Griek
<http://www.jvdg.net/>