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I've changed graphics cards in my PC and now Windows 7 (32bit) is reporting that I have a whole gigabyte less physical RAM in my PC. Why is this?

Firstly, the machine has 4GB of physical RAM. The old card was an ATI 2600XT with 256MB and the new card is an NVidia 9600GT with 512MB.

With the ATI card windows sees 3326MB. With the NVidia card, windows sees 2558MB.

I realise that due to address space restrictions I will not see all 4GB with 32bit windows, but why is there such a massive loss of RAM when simply changing cards (bearing in mind BOTH cards have their own RAM and borrow no main memory like some built on chipsets do). Would using 64 bit windows solve this?

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Even though the card has its own RAM the computer can't directly address it and still address your 4GB of computer RAM, because your 32 bit machine can only directly address 4GB. Don't know why it would use 1GB, exactly, but that's why it takes away from your usable memory. –  Beska Mar 22 '10 at 20:13

3 Answers 3

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Because it (probably) has 1GB of video memory, which has to be taken out of the 32 bit Vista 4GB address space.

32 bit Windows has to share 4GB between physical memory and all of the memory mapped devices installed in the system. That's why you typically only have access to a bit more than 3GB of memory even with a lesser graphics card.

If you move to 64-bit Windows, the address space is much larger so you won't run into that issue and will get your full installed RAM. One downside though is that programs will actually use more memory, mostly because the size of pointers is larger.

EDIT:

It doesn't matter that the card has it's own memory. You still need address space for it's memory to be mapped into. I just noticed in the post that it's a 512MB card not a 1GB card, so there may be something else at work beyond the delta of 256MB that you will lose from the address space for the increase in card memory.

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1GB of video memory? At 32 bits per pixel, on 4:3 monitors, that would be more than 16,000 x 12,000 pixels. Am I missing something? Ooh. Maybe a lot of that memory is used for cached textures or something? Hadn't thought of that... –  Beska Mar 22 '10 at 20:08
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@Beska: Yep, most of the memory is for things like texture cache and geometry storage (you want all of your polygons in fast video memory, where the GPU can rapidly crunch numbers to draw the pixels 60 times or so a second). –  Eric J. Mar 22 '10 at 20:14
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Yeah it's only a 512MB card, so how can it take an EXTRA 1GB over the old ATI card? That's the bit I don't get. I would expect to lose an additional 256MB, but that's all. –  NickG Mar 23 '10 at 12:19

Check the BIOS and see if the memory reported there has changed.

Then run memtest86+ from bootable media and see what that reports.

If possible, put the old card in and see if any of these numbers change.

Then, post the information here. This will help sort out whether it is a hardware, driver, or windows issue.

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+1: Video cards with 512MB of RAM (or more) don't steal any System RAM away (beyond the BIOS load, regardless of 32-bit or not), something sounds "broken". –  Ƭᴇcʜιᴇ007 Mar 22 '10 at 22:38

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