The general idea behind a globally unique identifier
, or GUID
, is that it is in fact, globally unique
. This means that no two computers anywhere could possibly
generate the same GUID. There is a program, called guidgen.exe, that (by using a weird algorithm
based on time, MAC address
, and a few other conditions; it is published) produces them. It's a 128 bit field, thus yielding a possible 2^128 number of guids. Guids are usually only generated by developer
s, so it's a fairly safe bet.
They are used in describing uniqueness, especially of controls in the registry
. The GUID of the app server or control is built in, so for instance, Excel
has the same GUID, no matter where you install it. (Excel.Application of Excel 2000, should be the same everywhere. Use regedit
and some time and search for it). You can look in the ROT
to see what objects are running. Microsoft
has used them for other reasons that identify people or computers or what not, but generally they are used for CLSIDs of COM object
s to avoid a namespace conflict
(by using a huge numerical space).