I have an old desktop PC which has a P4M900T-M2 motherboard. It currently has one Apacer DDR2-667 memory module but the motherboard can support two DDR2 memory modules. I'm planning to upgrade it to have 2GB of memory (1GBx2).

My question is, do I need to have two identical memory modules?
Or will it work fine if I just install a different one to be paired to the existing one?


You should follow what the motherboard manual recommends. Typically, you don't want to mix and match memory sticks.

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  • 1
    The motherboard manual doesn't say anything about memory stick pairing compatibility. Although, in the manual, there is a section for memory module Qualified Vendor List. Does that also mean if I avail a pair of memory sticks from any on that list, there's a guarantee it will work? – Abel Melquiades Callejo May 22 '14 at 13:02
  • In my experiences, the QVL is pretty accurate. You should feel comfortable installing a memory module from the list. – rrirower May 22 '14 at 13:06

Yes, performance will be better but it is a low-budget motherboard so forget about dual-channel DDR2.

  • Single-channel DDR2 memory architecture
  • 2 x 240-pin DDR2 DIMM socket support up to 4 GB
  • Support DDR2 667/533/400 DDR2 SDRAM.
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Memory can be a little complicated when it comes to this area.

Firstly does the Motherboard actually 'pair' the DIMM's my understanding is that DDR2 doesnt do pairing as such like DDR3 does (however its been a while since I touched DDR2). So they should run as separate DIMM's which is better for mismatching. If they motherboard does pair them it may cause issues. My experience is that some DIMM's work together some don't, no real science between it just pure luck... Worse cause scenario is that you buy the DIMM they aren't compatible and you have to buy the 2nd to match it up but would end up costing more.

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In my experience, pairing two DDR2 modules with two different brands bought at the same shop which put it together (and so they should sell compatible memory), worked but not perfectly: Even though both were 800MHz, when used together, the speed went down from 800 to 667MHz.

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