Do you happen to know how it does it? (I wouldn't know where to look, in the source code). Does it still work if you move the sources to another directory, from your current one? Does Pharo do a whole-disk search every time? (Or just when it doesn't find them?)
No, Pharo won���t search your disk, that would take way too long. Basically, the image tries to find the sources in two places:
1. the image directory
2. the vm directory
In reality Pharo tries to do a bit more. The places Pharo looks in are listed in OSPlatform>>potentialLocationsOfSourcesFile (and subclasses).
See also PharoFilesOpener>>openSources.
Note that the Pharo implementation has probably diverged a bit from the one that Squeak uses / used to use.
Cheers,
Max