Why are CUDA/Stream cores disabled?

[Sidiox]

What I don't understand is why cards like the 780, which is as far as I know very similair to the 780Ti, have cores disabled? Same goes for 290 and 290x, aren't they basicly the same chip? Why does the 290 have stream cores disabled? Apart from the power delivery and such why are those cores disabled on cards? And does the known 290 to 290x flash enable these cores, if so why would that work and why do the 290 ones have disabled cores? And why do they laser off cores on some chips, like nVidia does it? Would that just add cost for no good reason, I mean isn't flashing your card your own risk (a part from the fact that only a few do it)? 

[Guest GRRigger]

defective cores

[brownninja97]

increases the success rate 

[Freaky_spider]

because there is a part of the chip that is defect,

 

when they make the chips they make a big wafer and how closer to the centre of that wafer the higher the chances of there being no damage, so they have 100% of the cores, but when some cores are deffect they lock the cores at the set amount for the lower tier card

 

hope this helped (and is correct)

[sof006]

They are disabled for good reason and that reason being that if they were enabled it would cause severe system instability and if you go turning the disabled cores back on you run the risk of completely bricking your card.

 

Not worth the effort.

[Stonep11]

What I don't understand is why cards like the 780, which is as far as I know very similair to the 780Ti, have cores disabled? Same goes for 290 and 290x, aren't they basicly the same chip? Why does the 290 have stream cores disabled? Apart from the power delivery and such why are those cores disabled on cards? And does the known 290 to 290x flash enable these cores, if so why would that work and why do the 290 ones have disabled cores? And why do they laser off cores on some chips, like nVidia does it? Would that just add cost for no good reason, I mean isn't flashing your card your own risk (a part from the fact that only a few do it)? 

The GTX780, GTX 780ti, and the GTX Titan all have one GK110 GPU core.  The main differences between all of the cards is that the higher end (GTX 780ti) has all of the cores enabled while the GTX 780 has some disabled.  This is done because when the GK110 is made there is a chance that every core fails to meet certain requirements.  If not met, Nvidia can see this in testing and will cut off the cores until the GPU is stable.  Some of the GPUs may not reach stability and be recycled, some may be only slightly weakened and pushed to lower end cards, some may be perfect and send to the highest end cards.

[HiiraTeruyo]

I think Linus said during one of the WAN shows that the 290-290X flash was only (confirmed?) possible on the early batches of 290s. The rest can't be flashed I don't think.

[Sidiox]

The GTX780, GTX 780ti, and the GTX Titan all have one GK110 GPU core.  The main differences between all of the cards is that the higher end (GTX 780ti) has all of the cores enabled while the GTX 780 has some disabled.  This is done because when the GK110 is made there is a chance that every core fails to meet certain requirements.  If not met, Nvidia can see this in testing and will cut off the cores until the GPU is stable.  Some of the GPUs may not reach stability and be recycled, some may be only slightly weakened and pushed to lower end cards, some may be perfect and send to the highest end cards.

Ahh now I get it! So they just disable them, but I have also heared that they sometimes laser off cores so people can't renable them, why is that?  

[Stonep11]

Ahh now I get it! So they just disable them, but I have also heared that they sometimes laser off cores so people can't renable them, why is that?  

Really the same reason they disable them in the first place.  The GPU did not pass the standards of the manufacturer and even though it may be possible to enable those cores it could be a major risk of instability, possibly even cause problems with voltages across the GPU and failure as a whole, even ruining the card.  The 290/290X is a poor example of the norm here, because there is some controversy over the locking down of those cores.  So while everything I have said still stands, cores could also just be opened or locked down to create different tiers in the market for financial direction.

[Glenwing]

Ahh now I get it! So they just disable them, but I have also heared that they sometimes laser off cores so people can't renable them, why is that?  

 

They aren't always disabled due to defects; depending on how demand goes, they may have to purposely sabotage some to bring them down to the level of the others that are actually defective, because it's very unlikely that the ratio of GTX 780 orders to GTX 780 Ti orders will be exactly the same as the ratio of defective cores to perfect cores.

 

Yes you can "unlock" some cores if they don't fuse them off, you used to be able to do this with AMD's AM3 processors like the dual or triple core Phenom II chips that were based on a quad-core design.  Even then it's a lottery though, whether you get a real defective one or a sabotaged one.  If  you got a dual core Phenom II, sometimes you could unlock it to a quad-core, others couldn't but could get at least 3 cores, some couldn't unlock any more cores.  It's also worth noting that even defective cores might still be usable to the average user.  Only a certain feature might not work, even if it is one that the average user may not use, it can't be sold as the higher end SKU which promises that feature, even if all 4 cores work properly in all other situations.  In other words the chip has to be able to do every single function that is promised in the specs; if it fails even one, then it must be binned to a lower end SKU which does not promise that feature.

[Sidiox]

They aren't always disabled due to defects; depending on how demand goes, they may have to purposely sabotage some to bring them down to the level of the others that are actually defective, because it's very unlikely that the ratio of GTX 780 orders to GTX 780 Ti orders will be exactly the same as the ratio of defective cores to perfect cores.

 

Yes you can "unlock" some cores if they don't fuse them off, you used to be able to do this with AMD's AM3 processors like the dual or triple core Phenom II chips that were based on a quad-core design.  Even then it's a lottery though, whether you get a real defective one or a sabotaged one.  If  you got a dual core Phenom II, sometimes you could unlock it to a quad-core, others couldn't but could get at least 3 cores, some couldn't unlock any more cores.  It's also worth noting that even defective cores might still be usable to the average user.  Only a certain feature might not work, even if it is one that the average user may not use, it can't be sold as the higher end SKU which promises that feature, even if all 4 cores work properly in all other situations.  In other words the chip has to be able to do every single function that is promised in the specs; if it fails even one, then it must be binned to a lower end SKU which does not promise that feature.

 

Bit weird that they sabotage the cores though, I understand why they do it but it costs extra money to disable them. If I understand you correct with that Phenom II you could get a higher score in some tasks/benchmarks then others if they use different functions of the cores?

[S1lentThund3r]

AMD Used to do this also with their CPU's. I bought a Phenom II X2 550BE which was just the X4 950 with two cores disabled, one was defective and (through some BIOS magic) I actually turned on one of the disabled cores and it worked fine and OC'd as high as the two cores is was originally sold with. Really luck of the draw though, and its so much more random with GPU's than CPU's.