Ram now fast enough for use as cache?

[sunburnt]

Are ram speeds coming close to cpu speeds? Or are the published speeds clock rate and not data rate?
It looks like fast ram could replace cpu cache freeing lots of die space and reducing heat.

 

[hunter315]

Nope. DDR based ram will never be fast enough to use as cache, too many clock cycles necessary to read.

CPU cache is made of SRAM and the small space of the Cache means that L1 cache can be accessed in a single clock cycle, L2 can usually be grabbed in less than 5. Fast DDR3-1600 RAM has CL9 which means it takes 9 clock cycles to begin reading from it.

DDRSDRAM is great for fast bulk storage but is simply not fast enough to replace the close levels of cache.