APU use over 4GB barrier

[RobertAnderson]

I have a question about APUs and >4GB on a 32-bit OS. I assume that if I put 8GB of memory in the system then the video portion of the APU can use the space that the OS can't. Is this correct?

I just upgraded a broken MB to a A6-3650. Since I was not upgrading the HD I just left 32-bit Vista on the system and only bought 4GB thinking that is all that Vista can handle. Now I am thinking I should have just bought the 8GB kit since the APU should be able to use it.

 

[VirtualLarry]

As far as I understand, all of AMD's APU chips are 64-bit capable, so they should be able to use more than 4GB, either as system RAM or video RAM.

 

[Mark R]

The OS needs to be able to "see" the video memory. In other words, there needs to be address space available for it.

Windows desktop 32 bit OSs are crippled, and cannot "see" any memory beyond 4 GB. While you potentially could see all 4 GB, any "video" RAM will hide your "system" RAM.

Windows server 32 bit OSs, linux, etc. are not crippled and would be able to make use of the memory above 4 GB.

 

[BrightCandle]

Second on what Mark said, you wont get to use that addition 4GB if you use 32 bit Windows without PAE. There is no clever way to get around the limit like this.

 

[Blue Shift]

Additionally, older versions of Windows (definitely XP, not sure about Vista) also insist on keeping a copy of everything resident in GPU memory in system memory. Since I doubt they have special APU drivers to fix this, you could have 2 copies of everything the GPU needs in main memory.

 

[RobertAnderson]

Thanks. I think this answered my question which really should have been does the APU access the memory directly for the video memory, or does it use the OS to address the memory. Sounds like it uses the OS so it was a good decision to only go with the 4GB.