Thread: Mixing DDR3 RAM with different CAS Latency?

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    Mixing DDR3 RAM with different CAS Latency?

    I currently have 2x1GB DDR3 with 9-9-9-26 CAS Latency.
    I see they have 2x1GB DDR3 with 9-9-9-20 CAS for really cheap now.
    If I filled up my other 2 RAM slots with the 9-9-9-20 RAM, would that cause problems/crashes...?
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    Most memory controllers have separate settings for each bank. If not, you may have to resort to manual settings and force the CAS latency to the longer time - that should work fine.

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    If not, you may have to resort to manual settings and force the CAS latency to the longer time - that should work fine.
    Or, if the stock speed of the memory is higher than the FSB, downclock the memory to get an FSB: DRAM ratio of 1 and then it should be possible to get the 9-9-9-26 to run at 9-9-9-20..
    Last edited by Neo1; 01-20-2009 at 02:48 AM.
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    Hail to the king, baby. Akkernight's Avatar
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    Hmm... So if you want to upgrade your RAM, it ain't just plug and play? Or more specific, you can't just plug it into the motherboard and it all works fine?
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    Quote Originally Posted by Neo1 View Post
    Or, if the stock speed of the memory is higher than the FSB, downclock the memory to get an FSB: DRAM ratio of 1 and then it should be possible to get the 9-9-9-26 to run at 9-9-9-20..
    I'm already sort of doing that. My RAM is 1333MHz, but I run it at 1066MHz to match with my FSB...

    Quote Originally Posted by Akkernight View Post
    Hmm... So if you want to upgrade your RAM, it ain't just plug and play? Or more specific, you can't just plug it into the motherboard and it all works fine?
    Welcome to the wonderful world of computer upgrades.
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    Quote Originally Posted by Akkernight View Post
    Hmm... So if you want to upgrade your RAM, it ain't just plug and play? Or more specific, you can't just plug it into the motherboard and it all works fine?
    But you can. Usually, when plugging in multiple memory modules with different latency, the motherboard will typically use the highest latency to make sure all the ram modules work.
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    Quote Originally Posted by Elysia View Post
    But you can. Usually, when plugging in multiple memory modules with different latency, the motherboard will typically use the highest latency to make sure all the ram modules work.
    That is if you are lucky! If you are not so lucky, they run at the highest speed, and some memory reads randomly go wrong because the RAM isn't ready to deliver the data when the processor fetches it...

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    The tricky part is that all motherboards are different... but a setting could fix that.
    Installing the same latency memory should be just plug n' play (assuming they have the same clockspeed, as well).
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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    Quote Originally Posted by cpjust View Post
    I'm already sort of doing that. My RAM is 1333MHz, but I run it at 1066MHz to match with my FSB...
    Then try to force the modules to run @ 9-9-9-20 and test with memtest86, if it works then you can get a set of 9-9-9-20 modules and run them all at the same latencies...
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    Quote Originally Posted by Neo1 View Post
    Then try to force the modules to run @ 9-9-9-20 and test with memtest86, if it works then you can get a set of 9-9-9-20 modules and run them all at the same latencies...
    Yeah, that sounds like a good idea. I'll try that before buying some new RAM.

    If I had to go the other way around and set the faster RAM to 9-9-9-26, could that cause any problems? I wouldn't expect it would, but who knows...
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

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    As has been pointed out, you are limited by the slowest RAM. Unless you literally can't buy the slower RAM anymore, I'm not sure why you'd get faster RAM (unless it's actually cheaper) only to have it run as slow as the slowest RAM. At today's prices I'd simply throw away your slower DIMM and start over.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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    Quote Originally Posted by brewbuck View Post
    As has been pointed out, you are limited by the slowest RAM. Unless you literally can't buy the slower RAM anymore, I'm not sure why you'd get faster RAM (unless it's actually cheaper) only to have it run as slow as the slowest RAM. At today's prices I'd simply throw away your slower DIMM and start over.
    2GB of 9-9-9-26 RAM costs about $75.
    2GB of 9-9-9-20 RAM costs about $50.
    Don't ask me why.
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

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    Quote Originally Posted by cpjust View Post
    2GB of 9-9-9-26 RAM costs about $75.
    2GB of 9-9-9-20 RAM costs about $50.
    Don't ask me why.
    Probably because they aren't making it anymore.

    Given that new info, I'd probably eBay my old DIMM (wouldn't expect to get $75 for it, but at least something)
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  14. #14
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    Quote Originally Posted by Neo1 View Post
    Then try to force the modules to run @ 9-9-9-20 and test with memtest86, if it works then you can get a set of 9-9-9-20 modules and run them all at the same latencies...
    I just tried setting my underclocked RAM to 7-7-7-20 and Vista's Memory Test didn't find any problems. I think I'll get the faster RAM and just leave it set to 7-7-7-20.
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

    "the internet is a scary place to be thats why i dont use it much." - billet, 03/17/2010

  15. #15
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    OK, my 4GB OCZ Platinum RAM just arrived.
    When I plugged in both that and my old 2GB OCZ Gold RAM, my system wouldn't boot, but if I only plugged in 1 of the OCZ Gold modules in along with my new RAM (with a total of 5GB) then everything boots just fine.

    Any ideas why it would boot with 5GB but not 6GB? I'm guessing it has to do with having both of them in dual channel mode at the same time...
    "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008

    "the internet is a scary place to be thats why i dont use it much." - billet, 03/17/2010

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