[yakubin]

Unix time is not UTC-based. It counts the number of seconds passed since a certain point in time, which may be described as date and time expressed in any time zone you like. It just so happens that in UTC it is easiest to remember for a human what this point was, since you get a lot of zeroes at the end.

Edit: I’m not entirely correct here, as aside from UTC the time zone, there is also UTC the time standard. See below.

[ericpauley]

Unix time is UTC-based, in that the leap second corrections applied to UTC are also simultaneously applied to Unix time (as people tend to use it).

[yakubin]

I stand corrected. As I’ve double-checked now, unfortunately “UTC” is ambiguous in that it may refer both to the time standard and the time zone. In this case one can say that Unix time is based on UTC the time standard, but not the time zone. Although given that in Unix time every day has the same number of seconds and instead the clock is sometimes slowed down, while in UTC there is an additional 61st second, can we truly say that it’s UTC-based? I’d say it’s its own standard derived from UTC. Maybe that’s being too pedantic.