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How can I tell what RAM will fit my computer?

I have a Pentium 4 computer, 2.40 Ghz, with two ddr memory modules. The former module is reported as DDR (PC2700) and the later is a DDR (PC2300), 256 MB each. The motherboard is ASUSTek, P4B533VM and supports up to 2 GB of RAM, 5 memory slots.

I have two other memory modules, 512 MB each, DDR, 400, CL3, PC3200U (as written on their labels).

The questions are:

  1. Will the "two other memory modules" work on my computer?
  2. Should I remove the old modules and use only the new ones or should I add the new modules?

1 Answer 1


To 1: The two modules should work, as memory is downwards compatible (as long as it's still DDR), although the maximum speed is defined by the slowest module. (see similar question Is PC4200 DDR2 compatible with PC3200 DDR?) Since your motherboard only supports PC2100, you are not running faster than 133 MHz (PC2100) anyway.

To 2: It should work, but it's not recommended to mix modules of different brands or specs. In your case you probably don't get much more performance by keeping the 256MB modules anyway.

edit: Source for motherboard specs: http://www.asus.com/999/html/events/mb/socket478/p4b533-vm/overview.htm

  • Why isn't it recommended to mix modules of different brands or specs (as long as the motherboard supports them)?
    – devius
    Jun 4, 2012 at 14:33
  • If you use sticks of different specs, they will all run at the speed of the slowest, or not run at all if they are not compatible. As long as all the specs match, it might very well work, even if you use sticks of different brands, but you can't be sure before having it tested.
    – schluchc
    Jun 5, 2012 at 6:08

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