All PROM versions are OK for recording.  
All listed PROM versions are backwards compatible.
ibaxb4 and obax17 fix all known performance problems with Mark5A.

ibaxb4 (or higher) and obax17 (or higher) are required for reliable
       playback.   If your version is ibaxb4 and obax17 or higher,
       and if you do not need the new features described below,
       there is no need to upgrade.

If you are programming a new board, or upgrading an old board,
use the highest version available.  All PROM files are fully
tested before thay are placed on this site.

The differences between the Input PROMs are:

ibaxb4 uses track 16 for checking Rack ID
ibaxb5 uses track  6 for checking Rack ID
ibaxb6 uses track  4 for checking Rack ID
ibaxb8 (or b7) is required for the 'in2net' command.

obax18 can play back disks with fill patterns that are
       inserted to replace lost data.  For more information, search
       http://www.haystack.mit.edu/tech/vlbi/mark5/UpdateMark5.html
       for "fill-pattern".

obax19 provides the "Throttled" flag.  For more information, search
       http://www.haystack.mit.edu/tech/vlbi/mark5/UpdateMark5.html
       for "throttle".

obax1a is original Mark5A+, never tested
obax1b is Mark 5A+ with no mode=mark5a+2:64
obax1c is Mark 5A+ with all modes

13 November 2006  - DLS