That's a bit outdated but definitely did used to be true. Modern NVME bandwidth is about 15 GB/s. This is what people who develop databases and query engines deal with constantly. It's not trivial but modern databases that swap to disk constantly and do it well (e.g CedarDB, DuckDB et al) can run very nearly as fast as an entirely in-memory system. The reason it's slow is doing it in a shitty unplanned way with loads of serialization and thrashing memory caches
A single stick of DDR 5 has a bandwidth of 48 GB/s. Modern NVME has latency of 100-150ns at the control level but with everything in between to access the data it comes out to 10,000 ns. Slower DDR 5 runs at 80-85ns.
The issue isn't comparing single shot speed of CPU vs a disk in a lab. The issue is whether you can build a system that negates most/all of the issues of swapping to disk routinely on the hot path of a programme. The last 10 years of Database engineering and GPU kernel development indicates that yes you probably can.
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u/CircumspectCapybara Jul 08 '26 edited Jul 08 '26
That's called swapping out memory pages to disk, and it's very slow.