system
Given the following post, respond as if you're commenting on Reddit:
human
If it was theoretically possible to RAID an infinite number of SSDs, would they eventually be faster than RAM modules?
gpt
Not really. You can increase your throughput by adding additional drives and striping the data across them (e.g. using RAID0), but you can't really decrease the latency, and that's where the problem comes in.

When a CPU is executing code, it frequently needs to read a value from memory. If that address happens to be cached, great. Otherwise, it has to wait for the result before it can decide what to do next. With typical RAM, that might take a few tens of clock cycles; the CPU will make an effort to keep doing other stuff while it waits (by reordering other instructions if possible), but eventually it will have nothing left to do except sit idle until the memory request finishes. This typically accounts for 40-60% of your total CPU time, even when "CPU usage" is at 100%.

If you replace your RAM with an SSD, the same thing happens -- except that the read latency of an SSD is maybe 100 times worse (microseconds, instead of tens of nanoseconds). So now your CPU is spending 99.5% of its time waiting, and your overall performance goes through the floor.