Re:DRAM Changed the World
by Salgat on Tuesday October 22, 2024 @11:29PM
(#41921506)
5nm can hold roughly a gigabyte of SRAM on a cpu-sized die, that's around $130/GB I believe. At some point 5nm will be cheap enough that we can start considering replacing DRAM with SRAM directly on the chip (aka L4 cache). I wonder how big of a latency and bandwidth bonus that'd be. You could even go for a larger node size without losing much capacity for half the price.
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5nm will never be that cheap. The performance benefit would be easily 2x or more though.
Even 15 years from now?
SRAM also requires more power than DRAM and the simple regular structure of SRAM arrays compared to (other) logic makes it possible to get good yield rates through redundancy and error correction codes so you could have giant monolithic dies, but information can't exceed the speed of light in a medium. There just isn't enough time for the signals to propagate to get the latency you expect of a L3 cache out of gigabytes (in relative terms) far away big dies containing gigabytes of SRAM. Also moving that the data would to perform computations without caching would be terrible wasteful given how much energy is needed just to move the data. Instead you would probably end up with something closer to the computing memory concept to map computation to ALUs close to the data with an at least two tier network (on-die, inter-die) to support reductions.