How many bytes are there in the memory page of GPU?

[ultrafly]

How many bytes are there in the memory page of GPU?
How many in NV25 and how many in R300?

I am sorry for my poor english.

 

[arjan de lumens]

What kind of pages are you talking about:

• Pages for virtual memory management? (Size: N/A - neither NV25 nor R300 supports virtual memory)
• Pages of AGP memory addressable from the GPU side through GART? (controlled by northbridge, not GPU; typically 4Kbyte pages, but can vary)
• DRAM pages, which need to be opened one at a time when doing DRAM accesses (unrelated to virtual memory)? (IIRC, about 0.5 to 2 Kbytes for DDR RAMs)

 

[Grall]

As cards today have 4-8 DDR chips on them, that is up to 16k memory directly accessible by the GPU. I'm not sure how many pages can be open simultaneously in DDR memory, but RDRAM can have up to 32 4k pages open (but that supposedly is at a huge power/heat cost).

*G*

 

[ultrafly]

What kind of pages are you talking about:

• Pages for virtual memory management? (Size: N/A - neither NV25 nor R300 supports virtual memory)
• Pages of AGP memory addressable from the GPU side through GART? (controlled by northbridge, not GPU; typically 4Kbyte pages, but can vary)
• DRAM pages, which need to be opened one at a time when doing DRAM accesses (unrelated to virtual memory)? (IIRC, about 0.5 to 2 Kbytes for DDR RAMs)

"However, it's much faster to touch memory that's in the same memory page (inside the RAM, not the AGP/CPU page) than to cross pages. "

I think it is the third.

 

[arjan de lumens]

Each DDR RAM chip can have open 4 pages at the same time. DDR-II can have open 8 pages. The page size I gave was for a typical DDR RAM chip. Also take into consideration the crossbar memory controllers of NV25 and R300 - each of the 4 controllers in in NV25 always accesses 1 DRAM chip at a time, whereas each controller (out of either 2 or 4 active controllers) in R300 always accesses 2 DRAM chips in parallel. So the page size, as seen from the memory comtroller, should be twice as big for R300 as for NV25.

 

[Simon F]

]

"However, it's much faster to touch memory that's in the same memory page (inside the RAM, not the AGP/CPU page) than to cross pages. "

I think it is the third.

That entirely depends on the RAM chips used, the amount of RAM, and the width(s) of the data bus(ses). It could be 512 bytes, it might be 4kb. Don't rely on it being the same on different graphics chips, even from the same manufacturer.

 

[RGB]

Each DDR RAM chip can have open 4 pages at the same time. DDR-II can have open 8 pages. The page size I gave was for a typical DDR RAM chip.

With DDR-II it is possible to have 8 open pages (it's an option), and that is likely to be the default on system DDR-II, but the only currently available graphics DDR-II chips only have 4 pages.