Optiplex 755 DDR2 800 RAM upgrade options / help - General Hardware - Desktop - Dell Community

Optiplex 755 DDR2 800 RAM upgrade options / help


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Optiplex 755 DDR2 800 RAM upgrade options / help

  • Hi guys,


    My Optiplex 755 (desktop) came with 2 1Gb 800MHz sticks and I'd like to add another 1Gb, i.e. 2 x 512Mb. I went with two 800MHz 512Mb PC2-6400 Kingston KTD-DM8400C/512 CL-5 sticks, supposedly compatible with Optiplex 755. Unfortunately, after the upgrade BIOS shows it at all running at 667MHz.


    Is this Kingston RAM simply incompatible with my 755, or there is some setting/jumper I'm missing? I was wondering if somebody could recommend Optiplex 755 (desktop) compatible DDR2 800 RAM? Thanks in advance.

    Message Edited by SM05 on 03-13-2008 01:41 PM
  • First, IMO 800MHz is a waste considering that speed difference between 667 and 800 is barely noticeable. Secondly, not many computers seem to be fond of 4GB 800MHz RAM. They either not turn on or revert to 667MHz.


    I would return those sticks or just stick with them. Perhaps the newer Optiplexes can use it properly

  • The config I've described actually makes it 3Gb (2 existing x1Gb + 2 newly added x512Mb). :smileyhappy:


    My other option is to get 2 more of x1Gb directly from Dell but that would (a) waste 1Gb because 32-bit Vista won't be able to address that 4th Gb anyways, and (b) supposedly push it to the setup you mentioned in your earlier reply. I've actually read a Dell support article describing Vista installation problems with 4Gb suggesting to remove 2Gb, install Vista, and then add those 2Gb back.


    And my yet another option is to ditch Dell's 2Gb and get all 4 sticks from the same manufacturer, hoping this (not being able to run at 800MHz) is a mixed sticks issue. Yes, I do want it to run at 800MHz. :smileyhappy:



    Message Edited by SM05 on 03-13-2008 07:04 PM
  • Did some testing tonight. If I leave just 2 new or just 2 old sticks in there then it runs on 800Mhz. If I mix original Dell RAM and new supposedly compatible Kingston one then it scales it down to 667Mhz.


    Did some more research and found this recent post:



    I can confirm that Dell and Kingston memory have different ranks shown in BIOS. So, at this point if I were to still try to get 800Mhz out of all sticks, my options are:

    1 - Return Kingston memory and get 2 more identical Dell sticks. Dell doesn't sell 800Mhz 512Mb sticks so I'd have to pay more for 1Gb ones.

    2 - Get 2 more similar 1Gb Kingston sticks and put 2 Dell sticks on eBay.


    In any case, if Optiplex is automatically scales down to 667Mhz with all 4 sticks installed regardless of their characteristics (as hinted on in the above post), then neither option would do me any good.


    I'd appreciate any other input. Thanks.

  • Hi SMO5,

    Sorry for the delay in getting back. I was out of "circulation" for a while and only got a chance to pop in the new DIMM's today.

    I am pleased to report that the 4 identical 1GB CRUCIAL DIMM's are now operating correctly at the full 800 MHz speed.

    To re-cap the Crucial Part # for the matched pair is :- CT2KIT12864AA80E.000. This Kit contains two identical matched 1GB 1Rx8 PC2-6400U-555-12-D0  (Crucial part # CT12864AA80E.8FE )

    I bought these from Komplett  who I think still have stock (€40'ish for the pair )but I believe the part is now discontinued by Crucial and is replaced by a CAS 6 offering (CT12864AA800 ).

    However if you are looking at 4GB then 2 x 2GB may be more cost effective BUT then again I am not sure how the OptiPlex 755 might behave with 2GB DIMM's.

    If I had to speculate as to what the real issue is I am inclined to think that DELL's particular implementation of the memory controller does not like mixed Rank DIMM's.

    Anyhow I now have 4 x 1GB RANK1 CAS5 Crucial DIMM's working at 800MHz so I am happy enough.

    Please bear in mind that I have not done any extended testing yet to be absolutely sure that there are no issues like memory related BSOD etc. Although from what I have read in the forums the OptiPlex 755 has been known to throw up BSOD's all by itself for a variety of reasons so its not any  indication of a memory incompatability problem. BTW there is a new BIOS release for the OptiPlex755. It's A08 . Even though it didn't address my original issue I rev'ed  up anyway !

    Hope this helps and good luck with whatever way you decide to go.

  • Thanks for taking time to reply. I'm glad it's working as expect for you now.


    For the benefit of others, here's Kingston 512Mb 800Mhz part # that worked for me:


    KTD-DM8400C/512 (or KTD-DM8400C6/512)


    I plain on getting 2 more 1Gb part #:


    KTD-DM8400C/1G (or KTD-DM8400C6/1G)