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Not really, SRAM(what most caches use) isn't just more costly is also consumes a lot more power. You'd be hitting thermal limits much sooner than with traditional DRAM.

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Is that right? Traditionally DRAM has used much more power because it requires a periodic refresh whereas the power consumption of SRAM is purely leakage. Now, maybe leakage power has grown so much in recent years that this is no longer true but if so I'd find that very surprising. Do you have any numbers?

In SRAM you get Leakage + Switching current. For cases like a cache where you're going to be constantly churning bits this can drive up power quite a bit.

I don't claim to be an expert so there are probably cases where it's lower. However when I was looking into fast RAM for storing data from an FPGA for a simple Logic Analyzer most of the SRAM was almost 2-4x what DRAM was for power consumption at the same storage size(with SRAM being a blazing fast cycle access).

A hardware project I worked on some years ago included a chip that contained a small SRAM and a lithium battery, all soldered right onto the board, as a form of nonvolatile storage. Some SRAM can indeed be very low-power, but caches are probably a different animal.

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