Vista 32 bit be able to see 4 gig ram?

BKSinAZ · 02-17-2009, 01:45 PM

I have 4 gig of ram (all the same brand of Corsair XMS) installed.
I also have a Nvidia video card that has it's own ram (500mb)

the bios sees 4069mb of ram (not counting the video ram)

Upon booting up, the memory test sees all 4 gigs of ram.

Upon entering into vista (32 bit), it only sees 3.25 gig of ram.
What gives?

**asidman** · 02-17-2009, 01:55 PM

32bit is unable to see more than that because it is limited in total to read 4096MB ie 4GB.
Why you ask?
2^32 = 4,294,967,296
4,294,967,296 / (1,024 x 1,024) = 4,096
Ok so it reads 4GB, whats the problem?

Ian Griffiths offers a more detailed explanation:

Quote:

To address 4GB of memory you need 32 bits of address bus. (Assuming individual bytes are addressable.) This gives us a problem - the same problem that IBM faced when designing the original PC. You tend to want to have more than just memory in a computer - you need things like graphics cards and hard disks to be accessible to the computer in order for it to be able to use them. So just as the original PC had to carve up the 8086's 1MB addressing range into memory (640K) and 'other' (384K), the same problem exists today if you want to fit memory and devices into a 32-bit address range: not all of the available 4GB of address space can be given over to memory.

For a long time this wasn't a problem, because there was a whole 4GB of address space, so devices typically lurk up in the top 1GB of physical address space, leaving the bottom 3GB for memory. And 3GB should be enough for anyone, right?

So what actually happens if you go out and buy 4GB of memory for your PC? Well, it's just like the DOS days - there's a hole in your memory map for the IO. (Now it's only 25% of the total address space, but it's still a big hole.) So the bottom 3GB of your memory will be available, but there's an issue with that last 1GB.

BKSinAZ · 02-17-2009, 02:58 PM

Quote:

Originally Posted by asidman

32bit is unable to see more than that because it is limited in total to read 4096MB ie 4GB.
Why you ask?
2^32 = 4,294,967,296
4,294,967,296 / (1,024 x 1,024) = 4,096
Ok so it reads 4GB, whats the problem?

Ian Griffiths offers a more detailed explanation:

I ask because my windows can only see 3.25 gig ram, not the full 4gigs.
Remember that I also have 512 on my video card.

**wrench97** · 02-17-2009, 03:22 PM

Windows can a address 4Gig total usually reports 2.8-3.5Gig as available any memory on the Video card or address space used by other system devices gets subtracted from the 4Gig number what you have left is usable address space for the user.

02-17-2009, 01:45 PM	#1 (permalink)
BKSinAZ Registered User Join Date: Oct 2004 Posts: 104 OS: XP Pro	Vista 32 bit be able to see 4 gig ram? I have 4 gig of ram (all the same brand of Corsair XMS) installed. I also have a Nvidia video card that has it's own ram (500mb) the bios sees 4069mb of ram (not counting the video ram) Upon booting up, the memory test sees all 4 gigs of ram. Upon entering into vista (32 bit), it only sees 3.25 gig of ram. What gives?

02-17-2009, 03:22 PM	#4 (permalink)
wrench97 Moderator, Hardware Team Join Date: May 2008 Location: S.E. Pennsylvania Posts: 18,481 OS: Win7	Re: Vista 32 bit be able to see 4 gig ram? Windows can a address 4Gig total usually reports 2.8-3.5Gig as available any memory on the Video card or address space used by other system devices gets subtracted from the 4Gig number what you have left is usable address space for the user. __________________ Power Supply and Selection