Member Avatar for SamRand5

Hello. I am trying to upgrade my ram. I have 4 slots. 2 are empty. Currently it runs on 2 sticks of 2GB DDR2 400Mhz. I wanted to just double it by adding what I already have in there but I guess the 400Mhz speed DDR2 ram is beeing phased out because I could only find one type of ram that speed and it was 2 sticks of 1GB ram. I know I can't jump up to DDR3 but if I do away with what I'm currently running on can I upgrade to DDR2 1066Mhz ram?

Also, I found this odd. I ran Speccy on my computer to find out what I have in there. Websites and forums are telling me that DDR2 400Mhz is PC2-3200. However, Speccy tells me that my sticks are PC2-6400. I don't really understand what the PC is about. However is seems that most PC2-6400 ram is DDR2 800Mhz. Does this mean that my 400Mhz might be able to run with 2 other sticks of 800Mhz DDR2? If so, do all the sticks need to be the same number of GB?

Also, if I did just go with the 2 1GB sticks of DDR2 400Mhz, can that run with the ones I already have in there even though they are different number of GB?

Thanks for your help!

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  • Latest Post Latest Post by hazzag1995

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Short primer and practical next steps for this upgrade (addresses the Speccy confusion, mixing speeds/sizes, and what to check first).

Speccy/Cpu-Z vs the sticker: module labels use the JEDEC "PC2-xxxx" bandwidth number, not a simple Hz clock. PC2-3200 = DDR2-400 and PC2-6400 = DDR2-800 — so Speccy showing PC2-6400 probably means the stick is rated for DDR2‑800 even if you (or a tool) called it "400MHz." The board/BIOS will still choose the actual running speed. (en.wikipedia.org)

Can you mix 400 and 800/1066 sticks? Usually yes — DDR2 sticks of different rated speeds will usually work but they all run at the slowest common speed and the loosest timings the system can safely use. It’s not guaranteed: voltage differences, SPD/timing incompatibilities or mixing registered/ECC vs unbuffered modules can cause instability or prevent POST. So check the motherboard spec first (as recommended) and prefer matched pairs if possible. (xsnet.com.au)

Capacity and type rules: mixing different sizes is allowed, but dual‑channel bandwidth works best with matched modules (same size in each channel). Don’t mix RDIMM (registered) with UDIMM (unbuffered) or ECC with non‑ECC — many platforms won’t boot if you do. Also remember a 32‑bit Windows install will not use >4GB reliably — move to 64‑bit to benefit from larger totals. (’s OS point was on target.) (docs.oracle.com)

Quick checklist to proceed safely:

  • Identify the exact motherboard model and max per‑slot (manual or vendor support site).
  • Read each stick’s SPD with CPU‑Z (SPD tab) or inspect the stickers to confirm PC2‑rating and voltage. (blog.silverpc.hu)
  • If budget allows, buy a matched kit (2x or 4x) of the speed your board supports.
  • If adding mixed sticks: install, set BIOS to Auto, then run MemTest86 / Windows Memory Diagnostic for stability; if unstable, align voltage/timings or revert to matched modules.

As suggested, a vendor/system scanner or the motherboard QVL will save guesswork. If anything boots oddly after install, remove the new sticks and confirm SPD/voltage before retrying.

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Member Avatar for webrocky

Firstly you need to check the specification and features of the mother-board of your pc. If it can handle the ddr2 1066mhz ram then you can replace and upgrade into ddr2 1066 MHz frequency ram. But please don’t mix the 400 MHz ram and 1066 MHz during installation. If you mixed it and install it then your computer wont boot and problem occurs.

Member Avatar for rubberman

If your mobo supports ECC ram, here is a link for 2x2gb sets from buy.com: http://www.buy.com/prod/4gb-kit-2-x-2gb-memory-for-dell-precision-workstation-670-pc2-3200r/234073551.html

Also, your operating system needs to be able to handle more than 4GB of ram. It will either need to be a full 64-bit OS, or supports the extended memory model to handle more than 4GB (applications will still only get 4GB or less each).

Edited by rubberman
Member Avatar for hazzag1995

Crucial will tell you what you got, and what u can upgrade to. Head to www.crucial.com and use their system scanner.

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