What year is the Unix epoch — "time zero" for Unix timestamps — and how do you peg it?

1970 → tub · case.

The Unix epoch is 00:00:00 UTC on 1 January 1970; every Unix timestamp counts the seconds elapsed since that instant. The date was a pragmatic, round choice made at Bell Labs in the early 1970s — close to when Unix was being written, and easy to reckon from. (An earlier Unix used a 1971 epoch that ticked 60 times a second, but a one-second tick counted from 1970 was cleaner and didn't overflow so fast.) Because the count was stored in a signed 32-bit integer, it overflows on 19 January 2038 — the "Year 2038 problem" — which modern systems dodge by widening the counter to 64 bits, good for another 292 billion years. Peg the year 19 · 70 → tub · case: a travel case floating in a bath tub.

Go deeper:

• Crash Course Computer Science — full series (PBS) — 39 short episodes tracing this whole timeline, from early computing through transistors, ARPANET and the World Wide Web. A great overview of every year in this deck.