Numbers every programmer should know is a reference of hardware latencies: L1 cache (1ns), memory (100ns), SSD (1ms), network (10ms). These span orders of magnitude and shape every performance decision in systems design.
Based on Jeff Dean's seminal analysis; values evolve as technology changes.
Typical latency hierarchy (approximate 2020s values):
L1 cache reference: 1 ns L2 cache reference: 7 ns Main memory reference: 100 ns Mutex lock/unlock: 100 ns Compress 1K with Zippy: 3,000 ns Network SSD read (4K): 150,000 ns Disk seek: 10,000,000 ns Network RTT CA↔NL: 150,000,000 ns