Reconciling assholes for nearly a decade.

ECC vs Non-ECC RAM

I have a Dell Precision 450 with 2x512MB ECC sticks of RAM, for a total of 1 GB. I would like to put in 2 sticks of 1 GB ECC RAM for a total of 3 GB RAM. Is this possible? Someone told my network admin that you can only put in 2 GB of ECC RAM in this computer and 4 GB of Non-ECC RAM.

I can't seem to verify this anywhere I look, every spec sheet (including product documentation) says that max RAM is 4096 MB, but doesn't say if that's ECC or Non-ECC.

Thanks.
Permalink Nathan 
March 23rd, 2005
http://www.kingston.com says, "This system supports both ECC (KTD-WS450E/xxx) and non-ECC (KTD-WS450/xxx) memory. ECC and non-ECC modules should not be mixed. "
Permalink Christopher Wells 
March 23rd, 2005
Time to ask the "someone" to name his source...or to just forget about him and assume 4GB is OK as long as you don't mix ECC and non-ECC.
Permalink Kyralessa 
March 23rd, 2005
"Someone" was the vendor we were going to buy the RAM from. I think my company is going to buy me 4x1GB Non-ECC RAM, and take my 2x512 ECC RAM.

I guess it's a win-win for me, but I'm really confused. I knew that ECC was slower, but I didn't realize it would reduce the available memory by half. My network admin said, "you lose all that address space to address the parity bits".

*shrug*
Permalink Nathan 
March 23rd, 2005
>> My network admin said, "you lose all that address space to address the parity bits". <<

Somebody doesn't know his IBM PC history. The early machines were 9-bit memory (one bit to hold the parity). Sometime around the SIMM/DIMM changeover, the parity bit started getting faked using a small SMD chip on the memory board (reducing cost).

According to Crucial's memory configurator, the Dell PW-450 has 4 slots which have to be populated in pairs. All must be filled with the same type (ECC/non-ECC). Maximum memory is 4gb, so using 1gb DIMMs is OK.

ECC memory is slightly slower, and costs more. But it will check for and correct certain types of memory errors, whereas the non-ECC memory will either just give you bad bytes, or raise a parity error (depending). Higher reliability can be acheived using memory with IBM's ChipKill technology (lame name, cool tech), that will correct most multi-bit errors.

What to buy depends on what your reliability needs are.
Permalink example 
March 23rd, 2005
Of course if they don't have the ECC modules then that could be another reason for the duff info.
Permalink Simon Lucy 
March 23rd, 2005
And the original PC had the first bank of 8k chips soldered in. There were sockets for the other three banks. Of course when my memory chip failed, it was one in the first bank.
Permalink Miles Archer 
March 23rd, 2005
If this is for your desktop PC, then don't sweat it. The kinds of errors that ECC corrects for are very rare.
Permalink Brad Wilson 
March 25th, 2005

This topic was orginally posted to the off-topic forum of the
Joel on Software discussion board.

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