How can I get my 64-bit computer to recognize all of my RAM

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.

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.

Solution 1:

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

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

Solution 2:

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 http://www.memtest.org/ or http://www.memtest86.com/).

Solution 3:

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

See http://support.microsoft.com/kb/978610.