DFS-0.9  - 8271 BBC B
DFS-0.98 - 8271 BBC B
DFS 2.10 - 1770 BBC B/B+
DFS 2.20 - 1770 BBC B/B+
DFS 2.22 - 1770 BBC B/B+
DFS 2.23 - 1770 BBC B/B+
DFS 2.24 - Master MOS 3.20  But why not a major version change?
DFS 2.25 - 1770 BBC B/B+
DFS 2.26 - 1770 BBC B/B+ Last for the B/B+. Why another B/B+ release after the Master?
DFS 2.45 - Master MOS 3.50  Why the big version jump?  

BBC B/B+ 1770 DFS Versions

The first release was 2.0j which was DFS in EPROM. Following this was v2.1 which is 2.0j in ROM.
The release of the BBC B+ 128 saw version 2.2 DFS released.
v2.2    Shift-Z Break function included to emulate the 8271
        Extra commands necessary to deal with the 64K of paged RAM in the B+
v2.21   No record of it's release or existence.

v2.22   Developed to fix an esoteric OSFILE bug.
        Also the 128k associated SRAM utilities have been tidied up to make them more user friendly.
		This version will not work in all BBC model B's fitted with a 1770 upgrade board.
v2.23   Cures the problem of v2.22 not working in all BBC's.
		
Master 128 1770 DFS Versions 2.20,24,25,26,27,28,29

V2.20   First Release
V2.24   Loading with OSFILE &FF returns A=1
        File saves>64K work
V2.25   CLOSE#0 and *CLOSE and *SHUT leaves files with correct length
        Writing to extent works correctly
        Unknown command as LIBFS works correctly
V2.26   OSGBPB speeded-up
        All four head step rates implemented i.e.
        *CONFIGURE FDRIVE       0       1       2       3
        for 1770                6       12      20      30 mS
        for 1772                6       12      2       3  mS
V2.27/8 Software patch for spurious Motor-on after 1770 reset
        Following fixed:
        If a) A file was open
           b) the disk had been changed
           c) BREAK was pressed
        then the old disk catalogue would be written to the new disk.
V2.29   OSGBPB tube problem introduced at 2.26 fixed
        *CONFIGURE FDRIVE 2 has software delay added to hardware delay.
        This allows for support of slow step rate drives with 1772
        fitted, ie
        *CONFIGURE FDRIVE       0       1       2       3
        for 1770                6       12      50      30 mS
        for 1772                6       12      32      3  mS