Why is GMT the standard for computer time instead of UTC?

time timezone utc gmt
Alexander Bird picture Alexander Bird · Jan 19, 2012 · Viewed 12.9k times · Source

It feels to me like everywhere I've seen time related algorithms in programming, GMT was the base time. For example, I was told to always store time in a DB in GMT+00 so that time zone changes don't disrupt anything.

  1. Am I right that GMT seems to be the base time zone in software development?

  2. If so, why not UTC? Why is it not common to say "UTC+01" instead of "GMT+01" considering that even Unix timestamps are defined from UTC (http://en.wikipedia.org/wiki/Unix_time)

Answer

Kris Harper picture Kris Harper · Jan 19, 2012

GMT and UTC are the same time. UNIX time is based off of UTC, so you might find that more on UNIX and *nix systems.

UTC is also more closely tracked as an official time (i.e. is more closely in line with "true" time based off of earth's rotation). But unless your software needs to-the-second calculations, it shouldn't make a difference whether you use GMT or UTC.

Although, you might consider which to display to users. One format may be more familiar than another. I would typically go with UTC for global applications, and GMT for European or UK-based applications.

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