Why does my computer say 24 GB ram 16 GB usable?

Windows 7 professional 64 bit
Gigabyte GA EX58-UD5
i7CPU 920@2.67Ghz 2.66 Ghz
Gskill Ripjaw f3-8500CL7S-4gbrl DDR3-1066 PC-8500 4gbx1 spd cl7-7-7-1 8 1.5v
24 gig ram 6x4
Nvidia Quadro FX4800

Recently my computer shows I only have 16 GB ram with 24 GB installed. I was forced to reinstall windows from another problem but I never noticed this prior to that installation. Is there something I need to do to make it "see" the other ram?

Thank you,
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David KrollCommented:
Try going into msconfig -> boot -> advanced options. And increasing the maximum memory and then running a reboot.
Bill BachPresident and Btrieve GuruCommented:
According to Microsoft, Windows 7 Home Premium has a maximum usable memory of 16GB.  Are you sure that you reinstalled Windows 7 Professional?
Thomas GrassiSystems AdministratorCommented:
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"Check the system configuration settings
 This problem may occur because the Maximum memory option is selected incorrectly. To fix this, follow these steps:
1.Click Start, type msconfig in the Search programs and files box, and then click msconfig in the Programs list.
2.In the System Configuration window, click Advanced options on the Boot tab.
3.Click to clear the Maximum memory check box, and then click OK.
4.Restart the computer.  "

This comes from
You may find the rest of the article interesting also.

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Joe Winograd, Fellow&MVEDeveloperCommented:
Nice article! Thanks for posting. Regards, Joe
joewinograd--Well, thank you.
Scott CSenior EngineerCommented:
Nevermind that is the first thing dkrollCTN suggested.
ScottCha--Actually the suggestion I made is to "clear" (reduce to 0) the Maximum Memory box, rather than to increase it as suggested by dkrollCTN.
artismobileAuthor Commented:
I may have found my problem if my failing memory in my head stirs. When I built the computer I bought and still have on disc windows 7 64 Home. 3 yrs ago I found out it wouldn't let me run 24 RAM installed. I went online and upgraded to Professional. I have no idea where the key is.  Something tells me I have to purchase it again.
Bill BachPresident and Btrieve GuruCommented:
When you look at the actual System Properties dialog, does it say Home or Pro?
Joe Winograd, Fellow&MVEDeveloperCommented:
Run msinfo32. The first entry in System Summary is OS Name. Is it Home or Pro?
Joe Winograd, Fellow&MVEDeveloperCommented:
Sorry about that...had a previous version of the page before your post sitting there. Regards, Joe
artismobileAuthor Commented:
It is home. 64 bit
Joe Winograd, Fellow&MVEDeveloperCommented:
OK, so that's the problem! 16GB max on Home.
Joe Winograd, Fellow&MVEDeveloperCommented:
Actually, 16GB max on Home Premium...just 8GB on Home Basic.
Bill BachPresident and Btrieve GuruCommented:
If only we had a chart that showed all that... ;-)
Joe Winograd, Fellow&MVEDeveloperCommented:
Yikes! Stepped on you twice in the same question...I promise it won't happen again. Btw, that's a great chart...excellent reason for getting W7 Pro instead of Home Premium.
artismobileAuthor Commented:
Yes, yes,,... My error. Glad I have you experts for the last 4 yrs. Thank you for all your help. May I just award to Billbach who initially made the suggestion?
Joe Winograd, Fellow&MVEDeveloperCommented:
Works for me! Although I really like the article that jcimarron posted.
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