Epoch
epoch
A fixed reference point in time from which a system measures elapsed time, most commonly January 1, 1970 for Unix systems.
Unix Timestamp
unix-timestamp
Overview
A Unix timestamp (also called POSIX time or Epoch time) represents a point in time as the number of seconds elapsed since the Unix Epoch: January 1, 1970, at 00:00:00 UTC. This simple integer representation makes it easy to store, compare, and transmit time values across different systems and programming languages.
The Year 2038 Problem
Systems that store Unix timestamps as signed 32-bit integers will overflow on January 19, 2038, at 03:14:07 UTC. After this moment, the timestamp wraps to a large negative number, potentially causing catastrophic failures. Most modern systems have migrated to 64-bit integers, which extend the range to approximately 292 billion years in either direction.
Usage in APIs
Many web APIs return timestamps in Unix format, either as seconds or milliseconds since the epoch. JavaScript's Date.now() returns milliseconds, while Python's time.time() returns seconds as a float. When exchanging timestamps between systems, always clarify whether the value is in seconds or milliseconds to avoid off-by-a-factor-of-1000 bugs.
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