Stewpit Indy questions <:-/ - test-drb@ccmp.vtda.org

15 May 2006

On May 15 2006, 10:08, Jochen Kunz wrote:
...
  On Sat, 13 May 2006 11:14:59 +0100 (BST)
 Pete Turnbull <pete at dunnington.plus.com> wrote:

 > ECC != parity. 
...
  I know. Sorry for not being clear in my previous mail.
I meant: Usually
...
  the terms "parity SIMM" or "ECC
SIMM" are used for SIMMs with 36 data
 bits. If the extra 4 bits are used for parity or ECC depends on the
 memory logic in the machine, not on the SIMM. 
4 bits in 36 isn't really enough for useful ECC.  That's why on SGIs
you sometimes see the error message "unrecoverable memory error" and
relatively rarely see "Recoverable memory parity error corrected by
CPU" :-)  Most ECC memory uses more bits, and 36-bit memory is rarely
described as ECC memory rather than parity memory.

...
  There are also some machines (some sun4c and some EV5
Alphas) that need
...
  33 bit RAM. They use one parity bit per 32 bit word.

True, though those will work with 36-bit memory as well -- they just
ignore the extra bits.  At least, that's true of the Suns; I've not
actually tried it in Alphas but I don't see why it should ever matter.

-- 
Pete						Peter Turnbull
						Network Manager
						University of York