Athlon + PC133: no ECC?

[Josip Loncaric]

Athlons do well on floating point, so we've been looking at building
some Athlon nodes for our cluster, using PC133 memory of course.  This
requires VIA's KX133 chipset (now) or KT133 (near future) or AMD's 760
(more distant future).

On June 5th, AMD finally released Athlons with full speed on-chip cache
(see http://www.amd.com/news/prodpr/20108.html).  These will come in
OEM 'Slot A' packaging for the existing Athlon motherboards (e.g. those
based on VIA's KX133 chipset), but 'Socket A' packaging will be
preferable.  The 'Socket A' Athlons will require the KT133 chipset from
VIA (see http://www.viatech.com/news/00kt133launch.htm), at least until
AMD gets its 760 chipset out the door.

So far so good.  Unfortunately, while VIA's KX133 datasheet at least
mentioned 'optional' ECC capability, the KT133 datasheet (VT8363 North
Bridge Controller, see http://www.viatech.com/pdf/productinfo/kt133.pdf)
makes no pretense of having any ECC features.

Our applications require a lot of RAM (16-32GB or so), and we expect
individual node uptimes of several months.  Windows users who reboot
their 128MB machines daily would not even see a problem, but we need
ECC. It makes me very uneasy to even think about tracking down an
intermittent memory problem in 32GB of RAM without ECC capability.

Am I correct in concluding that the new 'Socket A' chipset KT133 will
have *no* DRAM data integrity features?  Does anyone know if the current
motherboards based on the KX133 (the 'Slot A' chipset) actually *use*
ECC?  My reading of the Asus K7V manual is that while this motherboard
will accept an ECC memory module, there is *no* way to tell BIOS to use
DRAM ECC (only an L2 cache ECC mode is mentioned).  Moreover, the
datasheets talk about '64-bit system memory interface' in both cases, so
it seems that the KX133 optional ECC feature is external to the VIA
VT8371 chip.  Do any KX133 motherboards actually implement ECC on DRAM?

If ECC is indeed unavailable on VIA's chipsets, and AMD's 760 chipset
remains unavailable, things do not look so good for Athlons at our end.
How concerned should we be about the lack of ECC with fast Athlons? 
This issue may even force us to go back to Pentiums.  BTW, some
Linux compatibility issues with Athlons were also reported, such as the
MTRR setup and even DMA problems with certain ATA drives, but unlike the
ECC situation, those compatibility issues are presumably resolvable in
software.

Sincerely,
Josip

-- 
Dr. Josip Loncaric, Senior Staff Scientist        mailto:josip at icase.edu
ICASE, Mail Stop 132C           PGP key at http://www.icase.edu./~josip/
NASA Langley Research Center             mailto:j.loncaric at larc.nasa.gov
Hampton, VA 23681-2199, USA    Tel. +1 757 864-2192  Fax +1 757 864-6134