Just purchased (2) 256MB RDRAM (Rambus) PC-800MHz-45nS type memory ECC cards (used).
Dell Dimension 8100 rated for up to 2GB RAM, (4 RAM sockets) originally had (2) 64MB non-ECC + (2) 128MB ECC cards. Worked fine.

If I install the (2) new 256 ECC cards in Bank 1, leaving Bank 2 empty, PC won't boot.
(Also tested with known good 256MB cards I already had in another PC. Same situation.)
If I install the (2) 128 ECC cards, or (2) 64MB non-ECC cards in Bank 1, leaving Bank 2 empty, PC does boot.
If I install the (2) 128 ECC cards, or (2) 64MB non-ECC cards in Bank 1, and (2) new 256 ECC cards Bank 2, PC works fine.

Ran MemTest86+ for 13 passes (10 hours) with no errors, with (2) new 256 cards installed in Bank 2.
Looked up RAM at online memory store for this PC. States it will work with ECC RAM. (?? )
Read on another forum that there is no problem using ECC RAM in a PC rated for non-ECC. Just the ECC function won't work. (Do not know if this is true).

Can someone tell me why the PC will not run on these new 265MB ECC cards in Bank 1, but will run them in Bank 2 if original smaller (ECC or non-ECC) cards are also in Bank 1??

Any thoughts as to why this is happening?

Is it safe to use the 256MB cards in Bank 2, with the 128MB cards in Bank 1? (seems to be working OK)

Thanks...

When you have the (2) 128mb modules in bank 1 and the (2) 256mb modules in bank 2, does it read the correct physical memory or does it only read as having 256mb?

My Computer > Properties shows the correct physical memory each time.

Could it have something to do with the 256 sticks being ECC?

But then the 128 sticks are also ECC??

Any other thoughts?

UPDATE: Have the answer.

In this PC, all 4 memory slots must be populated. At minimum, slots 1 & 2 must have RAM, but slots 3 & 4 can have RAM or Continuity Modules.

Thanks all...