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I need to replace some Samsung 512MB DDR2 PC2-4200U 533MHz 1Rx8 M378T6553CZ3-CD5 sticks for 1GB sticks, but I am only finding a bunch of "PC2-4200" 1GB sticks. I am hesitate to buy because I can't seem to figure out what the difference is or if they are both the same thing.

Are they both the same or different technologies?

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up vote 2 down vote accepted

I believe the "U" suffix is referring to "Unbuffered" as opposed to "Registered" memory.

From Wikipedia:

In addition to bandwidth and capacity variants, modules can

  • Optionally implement ECC, which is an extra data byte lane used for correcting minor errors and detecting major errors for better reliability. Modules with ECC are identified by an additional ECC in their designation. PC2-4200 ECC is a PC2-4200 module with ECC.
  • Be "registered" ("buffered"), which improves signal integrity (and hence potentially clock rates and physical slot capacity) by electrically buffering the signals at a cost of an extra clock of increased latency. Those modules are identified by an additional R in their designation, whereas non-registered (a.k.a. "unbuffered") RAM may be identified by an additional U in the designation. PC2-4200R is a registered PC2-4200 module, PC2-4200R ECC is the same module but with additional ECC.

It is typical to leave the unbuffered (standard - non-error-correction) status off of the part number (i.e PC2-4200 is equivalent to PC2-4200U) but it could be that some manufacturers have chosen to explicitly state whether their memory is Unbuffered, Registered or so on.

If you have a standard home computer you will almost certainly want unbuffered memory.

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Sorry for taking so long to respond but your answer pointed me in the right direction :). – Damainman May 5 '13 at 12:23

They should be the same thing.

All PC2-4200 will fit in the same DDR2 slots .

One thing to lookout for is to try and the matched pair DIMMs if you can if you have more than DIMM on the motherboard, as mixed pairs might cause instability issues. If you use more than one DIMM, check 1. if they are from the same manufacturers and 2. if the layout of memory chips are all the same, then it would most likely be matched pairs)

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