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I've recently upgraded my system from 6GB of RAM to 12GB. Once I installed the new RAM, Windows 7 shows in my System Information that I have "12.0 GB installed (7.99 GB usable)". Although less common, the past few days I've also seen the system info jump down to "3.99 GB usable", but it seems to jump back up to 7.99 after a few reboots.

System Information Screenshot

I have an EVGA X58 motherboard, which maxes out at 24GB of RAM, so I know I'm not reaching my motherboard's limits. All 6 RAM chips are exactly identical. The only thing different about the 6 chips is 3 are new and 3 have been in the system for about 18 months. They're all G.SKILL DDR3 1600 (PC3 12800) triple channel chips.

I'm running Windows 7 Ultimate 64-bit edition with the latest BIOS firmware and driver updates.

Is my new RAM defective, or is it normal to need to manually configure RAM timing in the BIOS in order to recognize the additional RAM?

The fact that my computer can boot and Windows acknowledges its existence makes me think it may not be defective.

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@Moses, This question definitely is not a duplicate. It was asked nearly 5 years before that question and the problem and accepted solutions were completely different. – Dan Herbert Feb 6 at 5:17

4 Answers 4

up vote 13 down vote accepted

Check (and double check) that they are inserted fully.

I've come across this exact problem when the modules have been insufficiently inserted.

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I took out all of the new chips and inserted them again. This seemed to fix it! I would have never guessed that RAM can be inserted deeply enough to be recognized but not enough to be usable. Thank you! – Dan Herbert Dec 13 '10 at 2:26

Defective memory doesn't always cause Windows to fail to boot. It might be a good idea to try running memtest86 or memtest86+ (available from or

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This happened to me, returned the RAM and got a different brand: now no problem. – Richard Dec 13 '10 at 9:08

According to Microsoft, you could try :

  1. Change maximum memory option. Run msconfig, choose Boot tab, click on advanced options. ensure the Maximum memory checkbox were cleared.
  2. Update system BIOS
  3. Enable memory remapping in BIOS
  4. Change AGP aperture size in BIOS
  5. Check for bad memory modules
  6. Check memory arrangement into slots
  7. Check whether memory standoff cards are used


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When I’m looking to upgrade a PC for myself or somebody else I always go to Crucial Memory website that I trust very much and has proven to be a great help through the years.

This is the link, I run it on the PC that I’m rebuilding and it gives me information on my current memory Specs. and some guaranteed compatible upgrades. It’s a great way to find out what’s in the machine quickly.

When I run it this is what it reports:

Memory Type: DDR3 PC3-10600, DDR3 PC3-12800, DDR3 (non-ECC) Maximum Memory: 16GB Currently Installed Memory: 8GB Total Memory Slots: 4

Although it states that max the max memory it can run is 16GB I found other info regarding that subject. Here’s what my research discovered. The maximum amount of memory that your system can use is actually limited in two ways — not only is there a maximum amount of memory that your computer motherboard can accept, there is also a maximum amount of memory that your operating system (OS) can accept.

Windows 8 (32 bit)

Windows 8 Enterprise: 4 GB

Windows 8 Professional: 4 GB

Windows 8 Home: 4 GB

Windows 7 (32 bit)

Ultimate: 4 GB

Enterprise: 4 GB

Business: 4 GB

Home Premium: 4 GB

Home Basic: 4 GB

Starter: 2 GB

Windows 8 (64 bit)

Enterprise: 512 GB

Professional: 512 GB

Home: 128 GB

Windows 7 (64 bit)

Windows 7 Ultimate: 192 GB

Windows 7 Enterprise: 192 GB

Windows 7 Professional: 192 GB

Windows 7 Home Premium: 16 GB

Windows 7 Home Basic: 8 GB

Windows 7 Starter: N/A

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