SLI: 256x2 = 512MB onboard?

[Newad]

With two 256MB cards running in SLI what is my total effective onboard memory amount?

Is it then 512 or still 256?

(I'm looking for some good SLI explainations in relative plain speak if anyone has links to share.)

 

[Ackmed]

Its still just 256MB total usable memory if you have 2x256MB cards in SLI. Same goes for Crossfire.

 

[Newad]

Thank you Ackmed.

 

[Ronin]

nVIDIA's response

It's in their KB as well.

 

[gobucks]

the reason it is only 256MB is because both cards need access to all the textures rendered on screen, so they can't have different data in their onboard memories. I hate when people mis-advertise their cards as having double memory, like people are doing with the 7950GX2, claiming it has 1GB of ram since each GPU has 512MB.

 

[Newad]

I was thinking about getting a couple 6800GS 512MB in an SLI config.

MaximumPC says it'll best one x1900xtx.

These cards are hard to find though, even the 256 version.

 

[Matt2]

I think 512mb for 6800GS is overkill. Did the 6800 Ultra benefit from 512mb? Marketing gimmick me thinks. I would also look for reviews that are not from MaximumPC IMO.

6800GS SLI beating a X1900XTX is a long shot. I know my 7800GT SLI @ 510/1200 only managed to beat the X1900XTX marginally in real world gaming. 7800GT SLI destroys the X1900XTX in 3DMark06 if thats your bag.

 

[imported_spank]

Originally posted by: Newad
MaximumPC says it'll best one x1900xtx.

http://techreport.com/reviews/2005q4/geforce-6800gs/index.x?pg=1

after reading that i very much doubt 6800gs in sli will beat a single 1900xtx

 

[Ronin]

Originally posted by: gobucks
the reason it is only 256MB is because both cards need access to all the textures rendered on screen, so they can't have different data in their onboard memories. I hate when people mis-advertise their cards as having double memory, like people are doing with the 7950GX2, claiming it has 1GB of ram since each GPU has 512MB.

That's because the cards DO have 1GB of memory on them, genius.

 

[Ackmed]

Yes, total of 1gig. Its still pretty misleading, as they are not going to be able to use 1gig of video memory. Yet the advertise it like it is. I dont like it, its a lot worse than the old HD debacle of not getting the advertised gigs. Which wasnt a big factor long ago when HD'2 were just a few gigs, but now when they're over 500gigs, you're "losing" a lot more gigs now. WD just settles a law suit about this.

 

[JBT]

512MB 6800GS is useless. a 7900GT voltmodded has pretty much the same performance as a regular 7900GTX. Basically unless you are running OVER 1600x1200 with AA the extra 256MB of memory doesn't really help yet.

 

[bunnyfubbles]

Originally posted by: Ackmed
Yes, total of 1gig. Its still pretty misleading, as they are not going to be able to use 1gig of video memory. Yet the advertise it like it is. I dont like it, its a lot worse than the old HD debacle of not getting the advertised gigs. Which wasnt a big factor long ago when HD'2 were just a few gigs, but now when they're over 500gigs, you're "losing" a lot more gigs now. WD just settles a law suit about this.

True, my 60GB HD only "lost" 3GB, my 160GB HD "lost" 10GB, and my 250GB HD "lost" 18GB...

Since I'll double up (or more) on my drives I'll RAID 'em and report the total result of available space as opposed to just claiming the rounded off numbers.

But I'm not quite sure how good it would be for HD manufacturers to advertise true space available, becauase true space amongst HDs might differ (two different 160GB HDs I have are different by about 1GB yet they definitely do not perform the same - one is a new SATA, the other is an old first gen 160GB PATA). People might buy/demand the slightly larger drives (even if it is only a GB or two) as opposed to better over all drives and thus companies would shift in such a direction - although I'm probably just being paranoid.

 

[Ackmed]

I agree, its a mess that will only get much, much worse unless they do something about it. It seems way out there right now, but in years to come, 1TB drives will be upon us. And then 2TB, and so on. You're going to "lose" a LOT of gigs that way.

 

[Munky]

With HD's, I believe the listed capacity is based on unformatted drives, which does not sound that misleading. If the drive actually has 120gigs, but Windoze formats it so only 112 is useable, then it's not really the drive's fault. With SLI memory, it's different. If you had a 2x512mb 7950gx2, and tried to allocate a 1GB buffer, it's just not physically possible. The most space you can allocate is still 512MB, so listing it as a 1GB model is misleading.

 

[Ackmed]

I know they are different, but not that much. Either way, you do not get what they lead you to believe you get. There is no way to get the gigs they advertise. I dislike them both, but since there are a lot of people who buy into this kind of PR crap, I doubt its going to change anytime soon.

 

[Bull Dog]

Originally posted by: munky
With HD's, I believe the listed capacity is based on unformatted drives, which does not sound that misleading. If the drive actually has 120gigs, but Windoze formats it so only 112 is useable, then it's not really the drive's fault. With SLI memory, it's different. If you had a 2x512mb 7950gx2, and tried to allocate a 1GB buffer, it's just not physically possible. The most space you can allocate is still 512MB, so listing it as a 1GB model is misleading.

Going OT here, but oh well the OP's question has been answered. Not quite correct Munky. The difference comes from the fact that harddrive manufactures call a drive with 500,000,000,000 (500 billion) bytes in it a 500GB drive. In other words, to them,
1000 bytes = 1KB
1000KB = 1MB
1000MB = 1GB
1000GB = 1TB

but, in reality

1024 bytes = 1KB
1024KB = 1MB
1024MB = 1GB
1024GB = 1TB

and then I believe, when formatting you 2-16 MB of space depending on the size of your HD's buffer. Not 100% on that one, as I only have 8MB buffer drives and windows won't let me use that last 8 million bytes.

 

[TanisHalfElven]

@bull dog you explanation is right in a way but its also true that certain filesystems waste a lot of space.

 

[BucsMAN3K]

Like said above, both cards need to access all the textures, so the memory isn't shared.

It makes you wonder though, is it possible that drivers could be developed so that each card in SLI only stores what it needs for the section of screen it is rendering, effectively sharing the memory load? Or would you need a whole new chipset for that?