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4gb of video memory
- Thread starter Tempered81
- Start date
MarcVenice
Moderator Emeritus <br>
Most people seem to have no clue how SLI and/or Crossfire works.
Tempered81
Diamond Member
i must not have a clue, how is it not 4gb?
nismotigerwvu
Golden Member
Well physically I guess its 4 gigs.....
Tempered81
Diamond Member
so physically its 4gb, but if you monitor vMem usage, its 0 thru 1024mb?
Tempered81
Diamond Member
i dont know the answer to that.
True. jaredpace is right of course, it is 4GB of physical memory, but yes, CrossFire/SLi only use the GDDR of the first card.
Ummm, yes its 12MB of cache...? So the Q6600 has only 4MB of cache effectively?
Oh I think I see what your saying, a 2 socket system. Not 2 cores on 1 die. Even then, I dont know how the dual socket system acts, so it may act like a single socket system w/ 6MB, or it may perform/behave like a single socket system w/ 12MB... haven't had the opportunity to read up on it.
Keysplayr
Elite Member
That is "sort" of true in that all the memory on all four cards have the same data in it. So essentially, it is only 1GB of "data" being processed at any given time. The upside? If rendering SFR, the each card is responsible for 1/4 of the frame load. Leads to insane AA. Also if AFR is used, then each card renders a frame in sequence.
Card 0: renders frame 1
Card 1: renders frame 2
Card 2: renders frame 3
Card 3: renders frame 4
Card 0: renders frame 5
Card 1: renders frame 6
Card 2: renders frame 7
Card 3: renders frame 8
Care 0: renders frame 9
Card 1: renders frame 10
etc etc.
Tempered81
Diamond Member
review text says they are "radeon HD 2900Xt" four of them
Tempered81
Diamond Member
ah, good point, well 4x 3870 is even better, i presume!
SlowSpyder
Lifer
If it was 4 2900XT's that'd be quite the power hog.
nullpointerus
Golden Member
Not necessarily. A 1 GB video card does not consume 1 GB address space.
See Peter's posts here:
http://forums.anandtech.com/me...rthread=y&STARTPAGE=22
In theory, if a Quad-Crossfire system were loaded up with enough other peripherals, then yes, there might not be address space enough for the OS to load.
To put it plainly, four 1GB cards in SLI or Crossfire still only equals 1GB worth of frame buffer. This is because the CPU sends the vertex data to the primary GPU which then copies the data to the secondary GPU. So in the case of quad SLI or Crossfire, you now have four 1GB video cards that all contain the same 1GB of data.
Once the data has been completely rendered, the compositing chip then sends the frames to the monitor at the correct time and in the proper order. Since you would now have four GPUs all crunching away on the data instead of one, the number of completed frames per second increases dramatically. This is how SLI or Crossfire gets its impressive power.
Once the data has been completely rendered, the compositing chip then sends the frames to the monitor at the correct time and in the proper order. Since you would now have four GPUs all crunching away on the data instead of one, the number of completed frames per second increases dramatically. This is how SLI or Crossfire gets its impressive power.
nullpointerus
Golden Member
I don't think you read what I wrote (and linked to). If the cards individually use only 256 MB address space, that's only 4 x 256 MB = 1 GB drain on address space vs. your 512 MB drain on address space. So it would be 1.8 GB of RAM (out of 4) in a 32-bit environment, or worst case 0.3 GB of RAM. But we do not know how much address space a 1 GB card consumes.
graphics ram is not a cache. there isnt a copy of whats in the graphics ram anywhere else.
also the 2 cores on a q6600 do not have to have the same stuff in both of them.
it just has to have whatever thread that core is working on's stuff on it.
if they both happen to be working on the same data then yes whenever there is a write on one thread it would have to write through the cache to memory and then update the cache on both cpus if both were workin gon the same data that is getting written into.
that doesnt mean the caches cant have multiple threads, or if they arent working on the same thing it doesnt have to be the same data in both caches.
I don't know about you, but I don't consider SLI or Crossfire to offer 'impressive' power/gains.
As to the CPU/Cache statements. The only person who can really address that is the original poster (swtethan). I was simply trying to guess what he ment... I was not stating how (i think) cache on a cpu works. Oh I see, you were 'talking' to aka1nas?