
Why is RAM not put on the CPU chip? - truth_seeker
https://electronics.stackexchange.com/questions/175615/why-is-ram-not-put-on-the-cpu-chip
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rwmj
Interestingly we were working with a start-up which was trying to go in the
other direction. They want(ed) to locate RAM in dedicated servers away from
compute, rather like storage is today centralized in NASes. Of course it
requires insanely fast network interconnects.

(I'm not claiming this is a good idea, I'm actually rather sceptical, but
pointing out that there are companies trying this)

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truth_seeker
Upmem did exactly the reverse. They put CPUs inside Memory

[https://news.ycombinator.com/item?id=20766283](https://news.ycombinator.com/item?id=20766283)

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enz
Does L1-L3 cache can be considered as a sort of bistable RAM?

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ThrowawayR2
In some sort of technical sense, yes; it's made out of SRAM and one could have
the cache be mapped exactly to a block of memory that is the same size as the
cache.

In a practical sense, no, because it's structured as cache and accessing it is
more convoluted than direct access to a bare block of memory. See
[https://en.wikipedia.org/wiki/Cache_placement_policies](https://en.wikipedia.org/wiki/Cache_placement_policies)
for a description of the various types of cache structures.

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karmakaze
If you never loaded addresses outside of the cached memory locations either
explicitly or speculatively then without invalidation you could run entirely
in L3 so it would be serving as storage rather than cache RAM.

