For the guys who confused the power usages and other specs of the 7970 and 7990:
The 7970 has a 250w TDP or thereabouts so it uses about the same amount of power as the 6970. It actually may use a little more power at load but uses much less power than the 6970 at idle.
The 7970 die size is very small even though it has more than 4 billion transistors and is a little smaller than the 6970 Cayman die.
The 7990 will probably not need to be under-clocked any more than the 6990 was and it wasn't really under-clocked, only one BIOS on it was and the flip of a switch fixes that. The 7990 will be about as power hungry as the 690 at load, probably slightly more and will have about the same idle power usage as a single 7970 because of Zero core tech that completely disables secondary GPUs when not in use. That also means that the 7990 and CFX setups may be able to shut down secondary GPUs when not doing something that uses them like gaming even if the primary GPU isn't idling, a great feature to save power when a high end computer isn't doing any GPU heavy work.
There will never be a 2GB version of the 7900 cards. They would need a change to their memory controllers and that just won't happen. It would reduce performance unless AMD opted for a 512 bit bus upgrade and that is very unlikely so to get 2GB AMD would have to lower the width to 256 bits (or even lower) and that would kill the performance. without a huge memory overclock over reference designs which could create other problems anyway. If AMD or another company really wanted to they could disable two of the 64 bit memory controllers present in 7900 Tahiti GPUs to get a 256 bit bus without any hardware changes but like I said that would still reduce performance without a huge memory overclock.
However, there will be a cheaper 1.5GB version of the 7950 that reduces memory capacity without reducing performance outside of situations that use the extra capacity. The 7950 will probably perform similarly to a GTX 580 but that is pure speculation on my part as I have no evidence to prove that claim.
The reason memory capacity is tied to the bus width is that each chip uses 32 bits of that bus width. To remove or add chips you need to decrease or increase the bus width or have two chips share the same part of the bus (like in DDR3 system RAM, all the chips on the module share the bus to the CPU)and that last one may reduce performance anyway (but not nearly as much as decreasing the width of the bus). So with a 384 bit bus you preferably have twelve 32 bit chips. Capacity per chip is generally 128MB or 256MB (megabytes, not megabits) so 12 chips times each per chip capacity is 1.5GB and 3GB.
For anyone claiming that the 7900 cards aren't overpriced consider this: two Radeon 6870s, easily obtained for around $300, have almost identical frame rates (a single stock 6870 is about 53% a stock 7970) yet the 7970 costs another $250-$300. The increase in price does not justify the 50w lower TDP than two 6870s and the only raw performance benefit is in any game where 2GB of RAM per 6870 is not enough and 3GB is necessary, an unlikely scenario right now and probably for a while. The option to buy a second overpriced 7970 (or third or fourth) for crossfire to roughly double (or triple or quadruple) the dual 6870s performance doesn't help much but I'll admit it helps.
At least these 7970s have more value than the GTX 580 does but that's not a difficult accomplishment when the GTX 580 is so expensive when two Radeon 6950s can be had for the same price and run circles around the 580.
I'll also admit the benefit of reduced micro-stuttering and similar effects that plague most dual GPU setups from having a single 7970 instead of two 6870s but that depends on the person, game, the monitor, and less so on the rest of the machine. Unfortunately none of this is enough to justify roughly double the price for similar performance. And if you don't like the idea of two 6870s, well two 6950s and maybe two 6970s if you get a good deal can be had for less then a single 7970 even though they both would outperform it and still have an upgrade avenue for boards with three/four x16 PCIe ports like X58 and X79. (I won't count AMD boards because AMD CPUs can't handle the GPU horsepower even close to well enough)
Then there is also the option of dual 6870 cards paired with a single 6870 (trifire) and two dual 6870 cards (quadfire). Having a third or fourth GPU is shown to pretty much eliminate micro-stuttering in Radeon 6870 setups by Tom's in a previous article. And how much would those setups cost? well dual 6870 boards are expensive but the good one costs $400 and with a $150 6870 it costs $550 for trifire, in the price range of a single 7970 while having about 35-50% more performance without micro-stuttering problems. There are problems associated with this (the dual 6870 cards all have only 1GB of RAM per GPU and a few games don't like trifire/quadfire) but it's another solution to people whom want huge frame rates on a 1080p panel without spending as much as other solutions would cost for similar performance.
http://www.tomshardware.com/reviews/radeon-geforce-stutter-crossfire,2995.html
That is the article mentioned in the above paragraph. It was made a while before the 7970 came out so the 7970 isn't included but it does provide info on tri and quad crossfire 6870s.
I apologize about the huge rant but didn't want to leave anything out.
Facebook
Twitter
Instagram