As Charlie says, this is an endlessly fascinating question with no single ‘right’ answer, other than: DON’T put them all in on single folder, because as Charlie rightly says, that will be s–l--o–w for Windows to read, especially across a network!
So to start with, my Rule #1 would be to try to limit the number of files in each folder to a couple of thousand at most, if at all possible. If you use MMD files, remember that these count towards the total number of files in a folder (this is one reason why you might want to use a Central Folder for MMD files: see Config).
Rule #2 is: DON’T have a single top-level folder which contains all the subfolders. (For example, C:\Audio, then loads of folders ‘under’ that). Some programs read folders recursively, so you can end up twiddling your thumbs while the program reads ALL the subfolders. Instead, I’d suggest perhaps C:\CurrentMusic, C:\RecentMusic, C:\Oldies, C:\Jingles, etc.
Rule #3 is: you NEED a duplicate copy of the library on AT LEAST ONE other computer, to guard against sudden disk failure. Very embarrassing to have to say live on air 'well, I’ll play another song once our boffins have got the network working again, meanwhile let’s talk some more about today’s papers with my guests … '! Ideally, you’d have something like RAID arrays of disks on your file server(s) as well, but even a fairly simple software-based mirroring solution like AllwaySync ($30 per PC) will do the trick. Ideally, you’d have the full audio library on a) your playout PC; b) your ‘main’ file server for the network; and c) a ‘live backup data’ server PC.
Beyond those ‘golden’ rules, it really comes down to how you USE your audio files. Might you want a separate folder of Xmas songs, and/or Summer songs? Is it more important to keep each presenter’s ‘own’ files separate and easily available? You’ll almost certainly want a separate Ads folder, too. And Station Jingles. But do you want your presenter’s carts/jingles in THEIR folders, or in a Presenters Jingles folder? Only you (or actually, your station staff: librarians, rippers, presenters, producers, and techies) can answer all those questions. Get each of them to submit ideas and appoint one of each to hammer out a compromise which everyone can work with.
That’s really the best advice I can give you.
Of course, if it’s your own home PC you’re talking about … ?
BFN
CAD