eli5 Why do pcs need ram, when you can just use your ssd as one

Question

It’s a common knowledge that computers run on rams, any application run on a pc is temporarily stored in the ram. So why can’t we just dedicate 32Gbs of ssd storage to ram and have our pcs run on it? That way one could have a 256Gbs of ram easily, without the need of the ram sticks and for so much cheaper.

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Answer 1

If there isn’t enough ram, then that’s exactly what happens. The problem is that SSDs are much, much slower than RAM.

RAM has a speed of something like 20,000 MB/s (varies significantly), while SSDs are more like 500 MB/s. Even more importantly though is that RAM is particularly good for *random access*, and hence is good at switching between different sections without too much delay.