What is the rationale behind GUID design?

Question

I do not understand the GUID. I mean, I understand that they are a large random number with a trivially low probability of duplication, but why do they have such a strictly defined format? (I refer to most of my information from http://en.wikipedia.org/wiki/Globally_unique_identifier .)

Why not just make the GUID a completely random 128-bit integer and call it a day? It seems that all the restrictions and rules imposed on their creation will somehow reduce the entropy. Why are some bits reserved for format and option specifications? Why indicate a statement?

Options and format specifications are what really puzzles me. If this is just a random identifier, why would a GUID consumer care about what format it was in? This is a 128-bit random identifier. Isn't that enough?

Answer 1

Do not confuse chance and uniqueness.

Without strict formatting, where, for example, a MAC address is included, two machines can simultaneously generate the same random identifier. At the moment, it is no longer "globally unique."