why is some RAM not usable?

December 2, 2012 7:16 PM

Aw, Christ. Why does my computer properties say "12.00 GB (6.00 GB usable)"? If it can detect it, then that means I installed it right, so why isn't it usable? Please tell me this is something easy to fix!

This is Windows 7 we're talking about. Is this something I have to adjust in the bios?

posted by gnossie to Computers & Internet (11 answers total)

Microsoft has a page on it, can't guarantee it will help.
posted by BungaDunga at 7:22 PM on December 2, 2012

Your Motherboard or chipset may have limits to the amount of RAM they can handle. You'll want to consult the documentation for your hardware to determine what their max is. 32 bit versions will also if you are running a 32 bit version of windows it will have a smaller amount of RAM it can use.
posted by Twain Device at 7:24 PM on December 2, 2012

I'm assuming 64-bit. what edition of windows is it? (there are limits on usable memory for the lower "home" editions)
posted by russm at 7:27 PM on December 2, 2012

Response by poster: It's a 64 bit system.
posted by gnossie at 7:28 PM on December 2, 2012

the per-edition limits are here, and don't include a 6GB step for Win7, so I guess that's not it.
posted by russm at 7:31 PM on December 2, 2012

Are you mixing RAM of different speeds?
posted by Nomyte at 7:46 PM on December 2, 2012

I suspect your system cannot support this amount of memory, or you've got a triple channel system and asymmetrical DIMMs or something. What's the model number of your motherboard or computer?
posted by tracert at 7:49 PM on December 2, 2012

Yeah, 6GB sounds like a dual-channel mismatch (2x4GB are dual-channel and working, it's discarding the other 4GB because it's not paired with a dual-channel pair), OR.... by some crazy fluke, you've portioned off 6GB of RAM to your on-board graphics. Some on-board graphics can use system memory for themselves and that will result in similar behavior, but that's usually at MUCH MUCH smaller levels, like 128-256MB, because most on-board graphics systems can't even address 6GB of memory.

If your configuration is 3x4 or 4x2, 4x1, there's likely a problem with the way your motherboard handles RAM, and dual- or triple-channel stuff, or as others mention, speed mismatches. (Though typically in a speed mismatch, the system defaults to the slowest, but they all have to run at the same speed usually.)
posted by disillusioned at 9:52 PM on December 2, 2012

How did you get to this position? Did you add extra memory or did you build the system yourself?
posted by epo at 6:06 AM on December 3, 2012

Is your 64bit version of Windows 7 the Home Basic edition? You might be hitting its 8 gig limit, and the OS is reserving some, leaving you with 6 gig?
posted by at at 6:15 AM on December 3, 2012

I'm with @Twain Device. I think it might be a chipset limitation. What model PC or motherboard do you have?
posted by cnc at 12:40 PM on December 3, 2012