Unix users around the world will witness an historical moment in computing history at 3:31:30 pm Pacific time (23:31:30 GMT) today when the Epoch Time Clock rolls over to 1234567890.

The clock was started on 1 January 1970 and is used to measure Co-ordinated Universal Time on Unix systems. Parties are planned in San Francisco, London and Dubai to mark the event, called by some the "digital equivalent of the birth of Christ".

While celebrations go on, however, the anniversary also raises the issue of what happens when Unix times runs out.

The original system for measuring time was recorded in 32-bit and as such can only store 4,294,967,296 seconds, or 136 years. This covers a period between 1901 and 2038, and Unix systems will effectively restart their clocks on 19 January 2038.

The so-called 'Unix Millennium Bug' may not be of serious concern to consumers or some business processes, but embedded systems developers are already looking at the issue.

Moves are afoot to change the clock to 64-bit time, which would last for about 293 billion years, giving our descendents more than enough time to sort out the problem.