KA655 is a faster-clocked version of KA650.  The board has been respun, the
visual appearance is noticeably different, but it appears that actual change is
almost zero, as later 650s used the newer ROM made for the 655.  The common
"old" KA650 ROM version is V1.2, and it feels much like KA630.  The DE is there
(diagnostic executive, the cool ROM diagnostic framework used on KA650+ series),
but no help, most of the new commands aren't there (like no SHOW DEV), and no
sweet utilities like CONFIGURE, SET HOST, KFQSA configuration, etc.  The one
common KA650/655 ROM version is V5.3, and that is the "new" one.  It is the same
for KA650 and 655 except for one byte in the second longword (SIE) which
identifies what board it is.  It tells the ROM what banner to scribble on the
console, and maybe how to set some timers (the boards are really identical
except for speed).  You can change a ROM image (as long as it's a "new" one)
between 650 and 655, as well as between -A and -B by changing the SIE longword
and recomputing the checksum.  In fact the power-up test countdown starts at 30
on the "old" 650 ROM, but on the "new" 650 it starts at 40 like on KA655, and
all aspects of diagnostics on the "new" 650 are like on 655, not like on the
"old" 650.  If you are trying to decipher diagnostic failures, you'll need the
655 manual, not the old 650 one.