FIDs are the actual files on the empeg's hard disk which contain the music, database entries, and playlists.

In other words, when you upload "Rush-Tom Sawyer.mp3" from your PC to the empeg, it does not get named "Rush-Tom Sawyer.mp3" on the empeg's hard disk. It becomes a FID instead. The FIDs are all stored in the directory "\drive0\fids" and "\drive1\fids" on the empeg's hard disks.

I don't know for certain what FID stands for, I think it stands for File Identifier perhaps. I'd be curious to know for sure.

Fids have two parts, the index file and the actual data file. The index file is the one ending in the number "1" and the actual data is the file ending in the number "0". For instance, on my player, the actual MP3 file of Tom Sawyer is "\drive0\fids\bf90" and the song's index/tag data is stored in "\drive0\fids\bf91".

The files that end in "1" are just ascii data containing the song or playlist information. For instance, on my player, \drive0\fids\bf91 looks like this:

duration=273946
bitrate=fs256
genre=Progressive Rock
file_id=01
type=tune
length=8767903
codec=mp3
artist=Rush
offset=1627
tracknr=1
ctime=1053562286
year=1981
source=Moving Pictures
rid=70d3fc79d7338bd1c897ebeae124d987
samplerate=44100
title=Tom Sawyer

Playlists are also FIDs. The difference is that their data file (the 0 file), instead of being the MP3, is a list of the sub-fids contained in that parent FID.

The way the empeg handles them is: Each time you synch with emplode, it sends a special command to the player software to rebuild the database. The player software then mounts the hard disks read-write, scans through every single FID, and concatenates all the index data into a database. Then it sets the hard disks read-only again and reboots. From then on, each time the player is booted up, this database is what gets loaded into the player's memory.

Having the song data indexed into this carefully organized database (instead of leaving everything as loose files named willy-nilly) allows the player to do all of the amazing things we take for granted, and do them instantly. If the player didn't use this structure, the software would do everything dog-slow, because it would have to scan the whole hard disk every time we asked it to look up an artist, or open the playlist menu, or even switched to the next track.