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:?: Can i install a 1GB DDR2 stick and a 256MB DDR2 stick together in dual channel mode ?
If i can't, then tell me to install them in the best possible way for the best performance .

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A quick, practical add-on to the replies from , and : a 1GB + 256MB DDR2 combination will usually work, but most motherboards will not present the entire 1.25GB as “full” dual-channel. Many chipsets use a partial‑pairing mode (often called flex or asymmetric mode) where the common portion between sticks runs interleaved in dual‑channel and the remainder runs single‑channel. In plain terms: 256MB from each stick can be interleaved, and the extra 768MB on the 1GB stick will operate single‑channel.

What to do practically:

  • Populate the slots exactly as the motherboard manual recommends for a two‑DIMM install (match the color/pairing).
  • After boot, verify the operating mode with a utility such as CPU‑Z (Memory tab shows channel mode) and check BIOS/UEFI for SPD and voltage settings.
  • If the system is unstable, test each module alone, swap slots, clear CMOS, and run memtest to isolate faulty DIMMs or incompatibility.

When to replace:

  • If you need full dual‑channel for memory‑bound tasks (integrated graphics, video editing, certain benchmarks), the clean solution is a matched kit (two identical sticks) so all memory is interleaved.
  • If everyday desktop use is the goal, the flex/asymmetric behavior is fine; the real‑world speed difference is modest unless the workload is heavily dependent on memory bandwidth.

Troubleshooting notes:

  • Check and, if necessary, set the DRAM voltage to the value printed on the module (DDR2 commonly 1.8V).
  • An updated BIOS can improve compatibility with mixed modules.
    These steps add the compatibility/behavior detail missing from earlier posts and will help determine whether to keep the mixed sticks or move to a matched pair.

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Member Avatar for Chaky

In theory you can.

What you need to know is which slots are of which channel. You can't mix different sticks on single channel. Usually, the layout is:
1st slot -1st channel
2nd slot - 2nd channel
3rd slot - 1st channel
4th slot - 2nd channel

After you plug them in correctly, the timings will be set to match slower stick. That is, if the dram settings in BIOS is set on "automatic".

Member Avatar for dcc

In theory you can.

What you need to know is which slots are of which channel. You can't mix different sticks on single channel. Usually, the layout is:
1st slot -1st channel
2nd slot - 2nd channel
3rd slot - 1st channel
4th slot - 2nd channel
D
After you plug them in correctly, the timings will be set to match slower stick. That is, if the dram settings in BIOS is set on "automatic".

Single channel is where you can mix different sticks, dual channel requires that the modules have the same specs.

The following is from Crucial.

Do I have to buy the same size upgrade as the memory module currently installed in my computer or can I mix different sizes?

In newer systems using SDRAM or DDR SDRAM memory, you can use modules of different densities with no problem. For example, if your computer came with a 128MB memory module, you can add a 256MB module for a total of 384MB of RAM. However, if you have a "dual-channel" system and want to take advantage of that technology, you will need to ensure that the modules in each memory slot are the same density.

Member Avatar for Chaky

You can't mix different sticks on ONE of the channels. They MUST BE IDENTICAL in order to work. I wasn't referring to the single channel motherboards.


Example:

1st channel (Slot A or C) 1 GB stick. Let's say slot A
2nd channel (slot B or D) 256 MB stick

If more RAM is required, and present one is to be kept, only way to expand memory is to get another EXACT stick (brand/model/capacity) and put it on the same channel where the previous one is. So, if the another 1 GB stick is to be used, then the only slot it could be placed in is slot C (appending to the example).

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