Power7 eDRAM vs. SRAM

[magellan]

Since eDRAM is still DRAM and so has to be refreshed, wouldn't it still be slower than
SRAM (maybe significantly)? I read some article that suggested that the Power7 was using wide bit widths in its 32MiB eDRAM cache (512 bits), maybe to overcome this issue? Does eDRAM use less power than SRAM?

I've also read a rumor that Haswell will have eDRAM cache that will be much larger than any Intel L3 cache to date. I'm not sure if it's true though.

 

[EarthDog]

Haswell is out and a quick google search (since I didnt know) turns up that it has the eDRAM.

 

[glussier]

Only intel Haswell hq processors with iris pro graphics will be equipped with 128MB of edram.

If you want more information on edram, see http://en.wikipedia.org/wiki/EDRAM

 

[Bobnova]

SRAM's problem is that most implementations take up considerable silicon room. That makes it expensive and difficult to get a lot into a small area.

 

[magellan]

SRAM's problem is that most implementations take up considerable silicon room. That makes it expensive and difficult to get a lot into a small area.

But SRAM also doesn't need to be refreshed, which I would think would make it faster than eDRAM.

 

[Bobnova]

Oh yes, extremely fast, it's just transistors, no capacitors involved. That's why it's used as cache. Very very fast, which can make up for the lack in density. That's also part of why CPUs have multiple cache levels.