On Nov 29, 2012, at 3:47 PM, Eugen Leitl wrote: > On Thu, Nov 29, 2012 at 02:19:26PM +0000, Lux, Jim (337C) wrote: >> >> >> On 11/28/12 11:46 PM, "Eugen Leitl" <[email protected]> wrote: >> >>> On Thu, Nov 29, 2012 at 01:14:39AM -0500, Mark Hahn wrote: >>> >>> I've been waiting for cache to die and be substituted by >>> on-die SRAM or MRAM. Yet to happen, but if it happens, >>> it will be with embedded-like systems. >> >> >> When running, SRAM consumes a lot more power and space than almost >> any >> kind of DRAM. 2-4 transistors per cell vs 1, if nothing else. > > Yes, but we're talking cache. Cache is SRAM with extra logic.
Correct, the L3 caches of most CPU's are simply SRAM. > Even a cache hit is slower than it would take to access on-die > SRAM. Cache coherency doesn't scale due to relativistically > constrained signalling. There also cannot be any such thing > as a global memory, unless you want it to be slow and spend > a lot of silicon real estate to make multiple writes to the > same location consistent. > >> A big problem is that the CMOS process for dense, low power, fast >> RAM is >> different than what you want to use for a CPU. And even between >> DRAM and >> SRAM there's a pretty big difference. (trenches, etc.) > > This is why we need stacked memories. Notice that MRAM might be > compatible > with CPU fabbing processes. ST-MRAM > http://www.computerworld.com/s/article/9233516/ > Everspin_ships_first_ST_MRAM_memory_with_500X_performance_of_flash > should have very good scaling in terms of performance and power > dissipation and can potentially be fabricated on top of an > ordinary CPU core http://www.cs.utexas.edu/~cart/publications/ > tr01-36.pdf > _______________________________________________ > Beowulf mailing list, [email protected] sponsored by Penguin > Computing > To change your subscription (digest mode or unsubscribe) visit > http://www.beowulf.org/mailman/listinfo/beowulf _______________________________________________ Beowulf mailing list, [email protected] sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
