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Mboard Memory Mapping XP/Vista

bilbat

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#1
Gotta (probably stupid) question... Have seen (I think in error) several magazine articles claiming you can't see a whole 4G in 32bit windoze as video card memory is mapped into the available adressable space; is this true, as I am planning a new development system, and would hate to lose a whole gig to a pair of 512M video cards for a non-gaming system; or, as I suspect, do you just lose a chunk to memory-mapped system I/O, and GPU's handle the actual video memory space? Need 4 monitors (1-logic design, 1-operator interface design, 1-AutoCAD electricals, 1-Visual Studio) but hate to give up a couple big xfire cards to maybe TRY a game or two; not, however, at the cost of a gig of system memory...

Gigabyte GA-X48_DQ6 w 2-300G WD Velociraptors in RAID0 for system & app's; 2-32G WD Raptors in RAID0 for swapspace; 2 1T Samsung SpinPoints in RAID1 for storage - thinking about a pair of Radeon 3850's, but only come w/at least 512M...

So long, and thanks for all the fish! :)

Bill
 

Polaris573

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#2
That is correct 32-bit Windows versions cannot utilize 4 gigabytes of RAM. However, the type and number of video cards has no effect on this. Maximum supported memory is 3 gigabytes regardless of your video card configuration. If you want to use all 4 gigabytes you must purchase a 64-bit version of windows.

I have never heard this being caused video card memory being mapped to the available address space. I thought it was a limitation of 32-bit programming being incapable of accessing greater amounts of memory. However, I could be wrong so someone please correct me if I am.
 
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bilbat

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#3
That is correct 32-bit Windows versions cannot utilize 4 gigabytes of RAM. However, the type and number of video cards has no effect on this. Maximum supported memory is 3 gigabytes regardless of your video card configuration. If you want to use all 4 gigabytes you must purchase a 64-bit version of windows.

I have never heard this being caused video card memory being mapped to the available address space. I thought it was a limitation of 32-bit programming being incapable of accessing greater amounts of memory. However, I could be wrong so someone please correct me if I am.
As far as the 32 bit limit - that's correct: 2 to the 32nd power = 4,294,967,296, or 4Gig; I am pretty sure the NUMBER of video cards will actually somewhat affect the available space, as my guess is that the video 'apperture' space is mapped; however, I want to be sure (before spending money to find out) that the actual video memory is not mapped to this space; I can get a PNY Quattro that will support four monitors (KDS 22"s at 1680x1050 for only $230 at NewEgg) and only has 128M or memory - but it's ~$430, plus another 50 or 60 for a pair of DVI splitters (comes with VGA splitters - someone in marketing's brain-dead); for way less than that, I can get a pair of ATI 3850's & run 'em in Xfire to occasionally run one monitor bodaciously, or all four for normal use, IF the video RAM itself is not actually mapped...
 
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#4
It is mapped into the available addressing space

"...32-bit Windows uses a flat memory address space, thus is limited to 4 GB of memory addresses. This is divided up 2 GB for individual user programs, and 2 GB for the operating system. It doesn't matter if you have 4 GB of RAM, or 512 Mb of RAM, it's the same virtual memory address space. This means that in order to directly address the memory used by video cards, and other such things on your computer, the OS has to be assign those specific addresses to that memory, and it's locked away and can't be seen - effectively making your memory address space smaller. ..."

Taken from the most concise explanation I've seen: http://msmvps.com/blogs/xperts64/archive/2008/03/18/32-bit-memory-in-x64-windows.aspx