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CPU Design: Fetch/Store vs. operating on memory (self.asklemmy)

submitted 8 months ago by wolf to c/[email protected]

8 comments fedilink hide all child comments

What are CPU designs which are not fetch/store but operate directly on RAM?

I only know about the design of the Nintendo Entertainment System (NES), where the CPU does not have registers (AFAIK) and operates directly on RAM, with fast access to low addresses in the RAM.

What CPUs/Systems do you know, which also do not do fetch/store for their operands? Which systems are out there? Why do CPUs like RISC/Arm/AMD64 use fetch/store, what are the tradeoffs? Are there different architectures for CPUs working on operands outside of fetch/store, DMA and stack machines?

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[–] [email protected] 3 points 8 months ago* (last edited 8 months ago) (1 children)

primarily speed. In order to avoid constantly searching for RAM, the majority of CPUs have a cache adjacent to them. It resembles a priority queue with VIP cache on a separate queue.

[–] wolf 1 points 8 months ago (1 children)

Thank you very much for your answer. I totally agree and understand why modern CPUs have registers. But what about low end/cheap (embedded?) hardware, any design/board/CPU w/o registers?

[–] [email protected] 2 points 8 months ago

Registers would only add very little amount of transistors to a CPU with huge gains, so even at the low end it isn't worth it.

These days low end is also crazy, you can get full fledged 32-bit microcontrollers for pennies.