Memory upgrade to 24gb only show 16gb usable


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Memory upgrade to 24gb only show 16gb usable

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So... I went ahead and maxed out the memory on my system and guess what... not all the memory is visible available

System details -

Studio XPS 9100

Intel I7-930 quad core processor

6x4096 DDR3-1600

Windows 7 Ultimate 64-bit

am updated on the most recent bios

The bios recognizes the 24gb installed but only sees 16gb as usable. In windows PC Wizard (CPUZ) can see all the modules but again only 16gb available to the OS. The OS limit is like 192GB. Why is the BIOS only allowing the use of 16GB instead of the full 24GB that it recognizes (yes I reset defaults).

What gives?

All Replies
  • so.. no one has answered even commented on this thread since I posted it and I still have no idea why my memory is being recognized but not used.

  • Is it showing 24GB installed and 16GB usable BOTH in the BIOS?  Try clearing the NVRAM/CMOS with the motherboard jumpers.

  • I have the same problem. It just happened today. I have an XPS 435T. I just upgraded the bios to the latest version.


    any ideas

  • Well, I have had this post up here for over a year now and no resolution. I also am on the latest BIOS rev and nothing. What is really frustrating is that the spec's for this machine indicate that it is supported. 

  • It seems like something is making it run in dual channel mode instead of triple channel mode. Depending on the tool I use I get different results. If I run PC Wizard 2012 it tells me that 24GB is installed but only shows me 4 dimms are installed when there are 6. When I run the crucial scan tool it  things that two slots are empty. The bios says that 24GB is installed but only 16 are usable.

    I have run memory checks on these modules and moved them around to no avail. When I search the internet it seems that this is a big problem with the x58 chipset and bios's but dell has never fixed it.

  • Mine now works. First I removed all the new memory and put in the old (9GB) started the computer and it showed 9GB

    Second, took out the old and replaced it with the 24GB (6 sticks 4GB each). Then booted to the bios. when I did i got a screen that had Bios or "Test Memory" I clicked on the Test Memory and after it ran went into the BIOS and it showed 24GB.

    Went in to Windows and it showed 24GB  without the 16 useable text.

  • I am happy you were able to resolve this. Unfortunately, this will not work for me :( I don't have a memory test feature native to the bios. The frustrating thing is that the full memory is detected in the bios. It says 24GB installed, 16GB usable.

  • 03fastmach1

    I am happy you were able to resolve this. Unfortunately, this will not work for me :( I don't have a memory test feature native to the bios. The frustrating thing is that the full memory is detected in the bios. It says 24GB installed, 16GB usable.

    Waste of time installing all that memory, chances are, you will never use all that memory.


    If my answer Was helpful?  Please let me know by clicking on the 'Did this answer your question' and clicking on the Yes button.  Thanks.



  • Robin,

    If you are not going to help with the problem, I would appreciate it if you just do not comment. Your statement is an ignorant one. You have no idea of whether I will use the memory or not as you have no ideas what kind of workloads I run on it. To me it is not a waste of time at all. This machine is supposed to have a maximum memory capacity of 24GB in a 6x4GB triple channel configuration. Presently it is down stepping it's performance. The system recognizes the memory but for some reason is disabling two of the memory banks.

  • Straight from Dell Manuals for your system

    Memory type

    1333-MHz DDR3 DIMM; non-ECC memory only

    You got the wrong memory

    My guess is it should still "Back Down" the speed, but it may have issues doing that and triple channel at same time.

  • Crucial had two memory spec's and I bought the higher one. I just replaced all the memory with the slower memory and it worked. UGH! My fault for not trusting the OE spec.

  • Can u tell me what was the spec of the memory? I have the same issue happening to me. i had 8gb installed on the studio xps 9100 and i purchased the 4 extra gigs of the same brand and spect of what was installed but it it wouldnt use the 12 gb it used only 8. Thx u in advance [ADMIN NOTE: Email ID removed per TOU policy]

  • I know it's 2.5 years later, but the Dell Manual on page 57 indicates 1066-Mhz not 1333-Mhz.

  • IMO, this is not a memory speed issue.  At all.  Memory comes with various SPD settings and will automatically clock down when and where appropriate.

    I ran into this issue and found this post, immediately resolving to post my findings after a resolution because this is inaccurate. 

    In my case, 24GB was found by the bios.  24GB can be found by CPU-Z.  16GB was reported in windows.  Windows 7 Home Premium offers a false 16GB limit.  Will upgrade to Win10 for a resolution.

    I recommend you use CPU-Z or equivalent tool to see the ram slots, what is reported, and the speed in use.