Time and data guides

11 guides with exact dates and tested snippets.

Unix time explained: what the epoch is and what it leaves out
The Year 2038 problem: when 32-bit Unix time runs out
Unix time in code: Python, JavaScript, Bash, PowerShell and Excel (all run)
Bits and bytes: the difference and why it matters for speed and storage
KB or KiB: kilobytes, kibibytes and why the two exist
Mbps vs MB/s: how to read your internet speed
UTC, GMT and time zones: what is the difference and how offsets work
ISO 8601 and RFC 3339: how to write dates and times
Leap seconds and Unix time: what happens and what is planned
How long does a download take? A table of sizes and speeds
How much storage do photos, music and videos need? Examples with counts

Where to start

For time, read "Unix time explained", then "UTC, GMT and time zones". For speed and size, start with "Bits and bytes" and "Mbps vs MB/s".

This is an independent guide. It is not connected with the IERS, BIPM, IANA, NIST or any company named here. Facts were read on 14 November 2026 from the sources named on each page; calculated values come from Python.