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I have 6 years old PC with 1.25GB (1GB + 256MB) of DDR2 533MHz RAM. As computer has become very slow and memory usage reaching its limits most of the times, i decided to upgrade RAM. But unfortunately, im not finding retailers selling DDR2 533Mhz RAM near my area.

Since I was not sure mixing up RAMs of different frequencies, i searched in web. Most results said they can be mixed but computer would run at lower frequency of the 2 RAMs. So I bought 2GB DDR2 667Mhz RAM expecting my pc to have 3GB RAM running at 533 MHz.

But computer properties page shows only 2GB RAM. BIOS settings too show the slot with 2GB 667MHz as ACTIVE and other slot with 1GB 533MHz as "NOT INSTALLED". When I removed 2GB RAM, they computer shows only 1GB RAM. So for some reason, 1GB RAM is not getting detected/used.

What is the problem here?

thanks in advance.

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Make and model of PC or motherboard? –  Dave M Apr 10 '12 at 17:02
    
Intel Pentium Dual Core 2.66GHz running WIN7 –  srinivas Apr 10 '12 at 17:05
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Afraid that is no help. Can you provide the make and model of the motherboard or the PC itself? Deytails will possibly expain RAM config needed/supported. –  Dave M Apr 10 '12 at 17:10
    
Hi Dave, my pc is an assembled pc (we buy different parts and get them assembled) so they dont have a make. Motherboard model is Intel D102Ggc2. –  srinivas Apr 10 '12 at 17:20
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it supports 2 gig of RAM max. –  stim Apr 10 '12 at 17:23
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2 Answers

Your motherboard could have a low maximum of total memory, 2 Gigs in your case. Otherwise your modules could be incompatible with each other. There some possible reasons and usually it is all about motherboard restrictions. For instance it might not support both single-sided and double-sided modules simultaneously. Other typical problems:

The "problem" is simply that different computer motherboards can accept memory in different, but specific, combinations. Some examples:

  • Some require that all memory sticks in the computer be identical. So if you have four slots, you can have 4x256meg, or 4x1gig, but you can't mix the 256meg and 1gig sticks.

  • Some allow you to mix, but you must mix in pairs. Meaning you might be able to have 2x1gig and 2x256meg.

  • Some require that if you mix, you must do so in a certain sequence. So you might be able to put 1gig in slot 1, and 256meg in slot 2, but not the other way around.

  • Many require that if you mix (according to whatever other rules there might be), the memory sticks share certain other characteristics, such as speed or others.

So, at least try to rearrange modules in different ways.

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It's also possible that this motherboard simply does not support more than 2GB in any combination (but we won't know that until OP provide that info, of course). –  Shinrai Apr 10 '12 at 17:19
    
Sure, thanks, I've added this point too. –  stim Apr 10 '12 at 17:25
    
Hi Tumar, earlier i was using two RAM chips (1GB + 256MB) in 2 slots of motherboard. Then my pc was showing 1.25GB of RAM. The problem is only now. As you said, i exchanged the 2 slots between 1GB & 2GB RAMs, on both cases, pc was showing 2GB RAM –  srinivas Apr 10 '12 at 17:25
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description of your motherboard. 2 Gigs is the maximum. So nothing with incompatibility. intel.com/support/motherboards/desktop/d102ggc2/sb/… –  stim Apr 10 '12 at 17:27
    
I was afraid of that, haha –  Shinrai Apr 10 '12 at 17:28
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Your motherboard only supports DDR2 533 & DDR2 400 SDRAM.

That means that 2GB DDR2 667Mhz RAM is not compatible.

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This is incorrect. DDR2 667Mhz RAM does not run at 667MHz, it runs at maximal 667MHz (actually 2x333MHz). Compare it with a street where people are allowed to drive 80kmph. You get a car which can do up to 100kmph, but it will do just fine at lower speeds. –  Hennes Nov 21 '12 at 13:09
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