Buffered/registers vs unbuffered/unregistered and ECC vs nonECC are two
different issues. What I am about to post is very general and thus not
accurate, but it should do.
ECC just adds error correction capability to the module. In most cases
you can use ECC or non-ECC memory, you just WON'T get the benefit of ECC
unless you use all ECC memory in a ECC capable system with ECC enabled.
ECC memory just adds additional bits to the width of the 'word' of
memory being transferred - instead of a 'word' being 8/16/32 bits
10/18/36 bits are transferred - the calculation and checking of the
'parity' is done by the memory controller. Most nonECC systems just
don't know they are there.
I have seen some vendors specifically state that ECC capable memory is
not supported on their board. I haven't tested it, so I don't know if
there was a 'real' hardware compatibility issue or the vendor didn't
what the hassles of someone putting ECC memory in and magically
expecting it to work.
What is the downside of using non-ECC memory? You don't know if what
your getting from memory is what you put there. Is it a big thing?
Depends. For most of us: no, the likely hood of a bit being corrupted
is very small. The enabling of ECC does slow the system down a little -
there is overhead in calculating the checksum when storing or retrieving
each word of memory. ECC memory is also more expensive as there are
more chips on the module to support the ECC encoding.
Registered and buffered memory are the same thing. The memory module
has a buffer register between the memory chips and the memory
controller. Why? Basically it is a signal booster. The memory
contoller can only communicate with a limited number of chips - each
chip it communicates with requires a little current and the controller
has a limited amount of current it can generate. The use of the buffers
reduce the number of chips it has to talk to directly. So, with
unbuffered memory the controller might be able to talk to 3 DIMMs worth
of memory chips, with the use of buffers it might be able to talk to 24
DIMMs - the limit here is the number of chips it can communicate
directly with not the amount of memory it can address.
Your system specs should say whether you need registered memory or not.
If it doesn't state, then it probably wants unbuffered memory.
If you system only supports 1/2/3/4 slots, it probably uses unregistered
memory. If your system is a server supporting 5+ slots, it probably
uses registered. Some systems are capable of supporting either, but not
both at the same time, certain Opterons for example.
If you are having problems finding the right memory for you system, try
one of the online retailers. Here are two that have a presence in France
or the EU.
http://www.crucial.com/eu/ http://www.kingston.com/frroot/