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I have a motherboard that supports dual channel DDR2 667Mhz slots with support for up to 4GB.

Will I have to put in 2 sticks with each running at about 667Mhz or will I have to have 2 sticks with each running at about 333Mhz to add up to that 667Mhz?

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Short answer: buy sticks rated DDR2‑667 (often labeled "DDR2‑667" or "PC2‑5300") and install them in the correct slots. You do not need two 333 MHz sticks to "add up" to 667. DDR2‑667 modules run on a 333 MHz physical clock but transfer data on both clock edges (double data rate), producing an effective 667 MT/s data rate.

Dual‑channel behavior and best practice: populate the matched pair slots (check the motherboard manual — slots are usually color‑coded). For best results use matched modules (same capacity, speed and timings). If you mix speeds or timings the motherboard will simply run all memory at the speed/timings of the slowest stick, and dual‑channel may fall back to single‑ or asymmetrical modes depending on the chipset.

Practical checklist:

  • Verify the motherboard manual for which slots form each channel and the maximum per slot/total.
  • Buy DDR2‑667 modules (same brand/model if possible) and install them in the paired slots.
  • Leave BIOS memory timing/voltage on Auto/SPD initially; only change manually if you know what you’re doing.
  • If the system is unstable after adding RAM, test one stick at a time and run a memory tester (e.g., Memtest86) to isolate faults.

Troubleshooting notes: reseat modules and clear CMOS if it won’t POST; older boards commonly expect 1.8 V for DDR2, so check voltages; faster RAM (DDR2‑800 etc.) will generally be downclocked to the board/slowest stick speed, as noted. The brief reply from is correct in effect — the installed modules will run at the supported/negotiated speed — but following the checklist above avoids most surprises.

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Member Avatar for rubberman

All of the ram will run at the full speed.

Member Avatar for gerbil

Or, to flesh that answer out a bit, you are meant to use sticks of DDR2-667 MHz RAM, with at least one stick per channel. If you go with 4 GB of RAM, then half the sticks in one channel and half in the other. Similarly for 2 GB. But if you have 3 similar sticks, add the third by all means to a channel - the controller will use it.
Best is if your sticks are matched. eg all DDR2-667 with similar timings.
If you use faster RAM, say DDR2-800 then the BIOS will normally adjust the Memory Strap ratio so that memory transfer rate matches FSB data transfer rate. For the same dollars, 667 RAM may well perform marginally better than 800 RAM because of tighter internal RAM timings. We're talking 1 or 2% here...

Edited by gerbil
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