4GB GTX 780?

[orangecat]

I haven't seen one but is there any?

[jacoblab1]

No, I don't think the 364bit bus would work with 4gb.

[Kuzma]

No there is not one, there will not be one and there should not be one - the memory bus is too small to take advantage of it >_<

[felixbearpig]

no, you can only double your memory, ie. 2 gb 770 4 gb 770

780 is only 3 gb becuase if you double he mem it will be a titan

[JORDANonPC]

no and manufacturers aren't allowed to add vram so there will never be anything but a 3gb 780 

[Emperor_Piehead]

No there is not one, there will not be one and there should not be one - the memory bus is too small to take advantage of it >_<

I thought you said the GK 110 can work around this and use the 6gb that the titan has?

[Glenwing]

Nope, it doesn't exist, and no one can make one (short answer).  If you want to know the technical reasons though...

 

The GTX 780 has six 64-bit memory controllers divided among the 12 SMX units in the GK110 core (aggregate, 384-bit bus).  Any RAM amount, then, will be in a multiple of six, otherwise it would mean one of the memory controllers is not being used, and in that case it would be counted (and read by software) as a 320 or 256-bit bus, depending on how many controllers were out of use.  Two of them on the 780, if you wanted 4GB of RAM, and it would leave you with a 256-bit but.  And the SMX units connected to that bus wouldn't be able to function.  Basically, it would be a GTX 680.

 

In fact, that is where the GTX 660 Ti spec comes from, it's on a GK104 core which has a 256-bit bus, but some of the SMX units are disabled, and therefore the 64-bit bus they are tied to is not used either, leaving it with only a 192-bit bus.

 

The GTX 780 has 12 DRAMs (each SMX has 1, and on the Titan each has 1 more on the back of the card).  Each DRAM is 256MiB for a total of 512MiB wired to each 64-bit bus on the core, 3GiB on a 384-bit bus total.

 

So, 4GB of RAM doesn't really work on the 780, it can't be divided and linked evenly between the 6 memory controllers.  (4096 divided by 6 is 682.666667 and no one manufactures DRAMs of that capacity )

[kaneandtaker]

If you need more than 3GB VRAM, get the Titan?