It's been a while (well, ok, a looonnng while), but I think it's

>>>B/2 Dxxx

- If I can remember, the 1 bit is "conversational" and the 2 bit is "single user",
  so B/3 Dxxx gets you both?

The number just gets put in a register (R5?) and is then interpreted by the
boot, so it could have been changed to mean something else.

Good luck with it, rick