Is a GUID unique 100% of the time?

Question

Is a GUID unique 100% of the time?

Will it stay unique over multiple threads?

Answer 1

Eric Lippert has written a very interesting series of articles about GUIDs.

There are on the order 2³⁰ personal computers in the world (and of course lots of hand-held devices or non-PC computing devices that have more or less the same levels of computing power, but lets ignore those). Let's assume that we put all those PCs in the world to the task of generating GUIDs; if each one can generate, say, 2²⁰ GUIDs per second then after only about 2⁷² seconds -- one hundred and fifty trillion years -- you'll have a very high chance of generating a collision with your specific GUID. And the odds of collision get pretty good after only thirty trillion years.

• GUID Guide, part one
• GUID Guide, part two
• GUID Guide, part three