UPDATED
offset explaination
00 "BB" header
02 low byte=1=get used sectors,hi byte=1=read disk conf
04 seems to be $0.w always?????
06 hi byte=sides
08 hi byte=sectors
0a hi byte=start track
0c hi byte=end track
0e sector size (bytes)
10 sectors per cluster??? Probably
12 cluster size (bytes)
14 root dir size (sectors)
16 FAT size (sectors)
18 FAT+bootsector size (sectors)??? Probably
1a bootsector+fat+root size (sectors)
1c number of clusters-1 (minus the contents of $1a offset)
1e pad? Seems to be 0 always??
UPDATED
Basically if you see "BB" at the start of the dim file, it's Fcopy. Otherwise it's ECopy.
Mail me if you have any other questions. I want to see full DIM file support on all future versions of our emulators

George