x86 memory allowance

Clum · 21 Dec 2009 at 17:22

I've always been under the impression that an x86 system could address about 4gb, but that also includes whatever VRAM you happen to have. So if you had 4gb ram and a 1gb graphics card, you would only be able to use 3 of your 4gb memory.

Is this totally wrong and infact the reason you can only have around 3gb available for use on an x86 system fitted with 4bg is that the extra gigabyte is being used for running the system ect?

Sorry, I'm just having one of those idiot moments where something you always believed in might not be true. Like the whole santa fiasco. There's no kids on here right?

milkinc13 · 21 Dec 2009 at 17:59

32bit yes,
so 4gb of ram with 1gb card would mean 3gb usable

Ross1234 · 21 Dec 2009 at 18:00

Its not that simple. You dont just minus the graphics memory from the system memory its rather more complex.

Clum · 21 Dec 2009 at 18:13

Right of course, I just simplified my point to get it across.

So I was right then....the video memory is a factor?

Ross1234 · 21 Dec 2009 at 18:14

It is a factor, yes. With your 6gb ram though you would be mad not to get 64bit.

Clum · 21 Dec 2009 at 18:37

I do run x64, the reason I ask is that someone was trying to tell me that vram isn't a factor at all unless it is onboard memory.

I can go and serve him a nice hot cup of shut the **** up now.

Thanks!

pastymuncher · 21 Dec 2009 at 18:54

When i had my 512mb 4870 and 4Gb of system ram i could only actually "see" 3.25Gb if that's any help.

setter · 21 Dec 2009 at 18:59

With 4gb system ram installed alongside a 1gb gtx 280 i could actually see 3.25gb as well using xp home 32 bit.

MeMeMeMe · 21 Dec 2009 at 19:45

The limit applies to 32bit OSs. See here for more detail than you might want. It's not just about graphics card RAM.

Corasik · 22 Dec 2009 at 00:33

setter said:
With 4gb system ram installed alongside a 1gb gtx 280 i could actually see 3.25gb as well using xp home 32 bit.

Graphics cards only map a window of their memory into system address space, My 8800GTX may have 768 meg on board, but it creates a 256meg window + a couple of smaller windows, total is about 320meg or so, my soundcard (X-fi) grabs around 128meg of address space, various other componants like the network card grab a bit more etc.

Overall its not the size of the GPU's ram, but the size of the reserved space that counts. So 3.25GB on XP home 32bit with a 1GB graphics card is not only possible, but actually common. Infact with some motherboards I believe that 3.5Gb is possible even with a 280GTX.

Windows (XP/Vista/7) 32bit also contains a secondary limitation, any single instance of a program cannot take more than 2GB of ram for itself (except under exceptional circumstances using PAE, and only Microsoft SQL server normally does that trick). Under 64bit windows a 32bit application is permitted to reserve and use 4GB of ram, and a 64bit application is allowed to reserve as much as it wants (anything in excess of physical ram will end up in the pagefile assuming you have a pagefile set)