32bit OS

ConTRo13R · 19 Jan 2009 at 00:44

The maximum ram for a 32bit OS is 3.5GB (yea?), so if i had two gfx cards with 1gb of vram each then will only 1.5gb of normal ram be allocated?

Or will .5gb of vram be unusable

bledd · 19 Jan 2009 at 09:47

just get a 64bit os mate, try out the Windows 7 x64 beta, it'll work until August anyway

you'll want 4gb ram though

Superficial · 19 Jan 2009 at 12:15

ConTRo13R said:
The maximum ram for a 32bit OS is 3.5GB (yea?), so if i had two gfx cards with 1gb of vram each then will only 1.5gb of normal ram be allocated?

Or will .5gb of vram be unusable

Burnsy2023 · 19 Jan 2009 at 13:41

VRAM takes precedence over normal system RAM IIRC.

gillywibble · 19 Jan 2009 at 13:58

Is the 0.5 gb of ram allocated at the BIOS stage?

If so, why is there a difference in allocation with a 64 bit OS?

Burnsy2023 · 19 Jan 2009 at 14:01

gillywibble said:
Is the 0.5 gb of ram allocated at the BIOS stage?

If so, why is there a difference in allocation with a 64 bit OS?

That .5 GB is for other system devices and stuff that uses memory mapped IO.

Fire Wizard · 19 Jan 2009 at 14:19

Hi ConTRo13R, the maximum amount of address space a 32-bit system has access to is 4GB and within this both your physical memory plus other critical functions that also need to map there memory resources into this space such as System BIOS, configuration for PCI/PCI-Express and any other memory mapped I/O functions such as your graphics card. These functions take priority over your physical memory which means they are all mapped first so if for example these functions take up say 1.5GB, it means that the address space is then cut down to 2.5GB which will then result in the system only being able to address 2.5GB of physical memory.

One of the main functions that result in this inaccessible space is due to your graphics card. The amount of VRAM that a graphics card has access too; a large portion of this is mapped into this address space.

gillywibble said:
If so, why is there a difference in allocation with a 64 bit OS?

Hi gillywibble, the reason why this doesn't affect a fully functional 64-bit system is because the address space is so large, it doesn't matter how many devices need to be mapped into this space, there will still be plenty of address space left for your physical memory or certainly for a very long time yet.

Take a look at this article here. It compares the address space to an office block which makes it very simple to understand why this "problem" if you like only affects 32-bit systems and not 64-bit systems.

ConTRo13R · 19 Jan 2009 at 14:56

Fire Wizard said:
Hi ConTRo13R, the maximum amount of address space a 32-bit system has access to is 4GB and within this both your physical memory plus other critical functions that also need to map there memory resources into this space such as System BIOS, configuration for PCI/PCI-Express and any memory mapped I/O devices such as your graphics card. These functions take priority over your physical memory which means they are all mapped first so if for example these functions take up say 1.5GB, it means that the address space is then cut down to 2.5GB which will then result in the system only being able to address 2.5GB of physical memory.

One of the main functions that result in this inaccessible space is due to your graphics card. The amount of VRAM that a graphics card has access too; a large portion of this is mapped into this address space.

Thank you very much Fire Wizard, that explains a few thing iv been trying to get my head around.

Thank you once again

Burnsy2023 · 19 Jan 2009 at 14:58

Ok, here's a question. Say you had 3 1GB graphics cards and something else that required a bit of memory mapped I/O, would the BIOS/OS reserve any main system RAM? Would the system boot?

ConTRo13R · 19 Jan 2009 at 15:02

Burnsy2023 said:
Ok, here's a question. Say you had 3 1GB graphics cards and something else that required a but of memory mapped I/O, would the BIOS/OS reserve any main system RAM? Would the system boot?

im guessing if that 'something else' took up .5gb the you would ahve another .5 to boot with.

If it took up 1gig then no it wouldnt, as the os cannot allocate any more memory, though you would get past the bios post

Or is that wrong?

Burnsy2023 · 19 Jan 2009 at 15:04

ConTRo13R said:
im guessing the other 1gb isn't already allocated therefore yes it would have 1gb of physical ram.

Or is that wrong?

Well you'd have some other devices that would take up a fair bit of that 1GB, so say there was nothing left, what would happen?

ConTRo13R · 19 Jan 2009 at 15:06

iv edited my previous post after reading it again

Burnsy2023 · 19 Jan 2009 at 15:09

ConTRo13R said:
If it took up 1gig then no it wouldnt, as the os cannot allocate any more memory, though you would get past the bios post

Or would the OS change the allocation priority of devices so there would always be some system RAM left? So maybe reduce the amount of VRAM allocated?

ConTRo13R · 19 Jan 2009 at 15:14

Burnsy2023 said:
Or would the OS change the allocation priority of devices so there would always be some system RAM left? So maybe reduce the amount of VRAM allocated?

I was thinking this but wasnt sure wheter it would make it past bios post, but it would as memory mapping is done by the OS.

In answer though id say yes it would deduct the minimun amount it would need to boot into the os from the vram

Burnsy2023 · 19 Jan 2009 at 15:15

ConTRo13R said:
In answer though id say yes it would deduct the minimun amount it would need to boot into the os from the vram

Any basis for this answer or just a guess?

I think it'll depend where the memory restraint is. If it's the BIOS, I doubt any remapping would be done. It's a lot of code for a fairly unlikely situation. If the BIOS supported over 4GB, then the OS may do some rejigging but I'm guessing.

bledd · 19 Jan 2009 at 15:22

"why do you need a 64bit os for over 4gb system + video ram?"

because stone cold said so.

far easier reply tbh

ConTRo13R · 19 Jan 2009 at 15:28

Burnsy2023 said:
Any basis for this answer or just a guess?

half guess, but also seems half logical too.

this has turned very interesting, from just a quick query

Fire Wizard · 19 Jan 2009 at 16:02

Burnsy2023 said:
Ok, here's a question. Say you had 3 1GB graphics cards and something else that required a bit of memory mapped I/O, would the BIOS/OS reserve any main system RAM? Would the system boot?

Since a large portion of the graphics card memory is mapped into the address space and not all of it, if you had 4GB of physical memory installed, I'm guessing there would still be around 1GB of physical memory that will still be addressed by the system after all memory mapped I/O devices have had there say. Even if the graphics cards you were using resulted in having to map 3GB of their memory resources into this address space, I can't see the likes of the System BIOS and other functions resulting in a total off 1GB being mapped into the address space. I certainly haven't come across any systems that need to map a whole 1GB of their memory resources into the address space for anything but the GPU, have you?

For arguments sake though, if all of the memory mapped I/O functions resulted in a total of 4GB, how would the system react? I'm honestly not quite sure what would happen. I wouldn't mind a definite answer to this though. Anyone up for a bit of testing?

All though, this really should be a non-issue since anyone that has a system that consists of multiple GPUs and are just using a sub-standard 32-bit system needs a good slapping in my opinion.

Ross1234 · 19 Jan 2009 at 16:08

i think if the two cards with 1gb ram were in sli, it would only take away 1gb addressable memory not 2 as the the information is duplicated.

Burnsy2023 · 19 Jan 2009 at 16:09

Ross1234 said:
i think if the two cards with 1gb ram were in sli, it would only take away 1gb addressable memory not 2 as the the information is duplicated.

Ok, they're not in Sli and I have a huge SCSI RAID array that takes up the remaining 1GB RAM? Are you happy in my hypothetical situation?