Date   : Wed, 11 Jan 1984 04:31:00 EST
From   : Jonathan W. Platt <JWP@mit-mc>
Subject: CP/M Plus

       I am in the process implementing CP/M plus on a new micro
being developed.  I hope someone can answer a couple of questions.

1]  The system manual says that the CSV and ALV, found in the drive's
    DPH can be in either bank 0 or bank 1 and yet there is no bank pointer
    for these.  How do they know where it is?  Do they check to see if
    the address is below common and assume bank 0 if it is?  Could
    they possibly be placed in bank 2, say?

    I am disappointed that it looks like the BCBs have to be in common.
    I know the hash tables can be put anywhere, but is there a way to
    put the XLT, DIRBCB and DTABCB tables in another bank instead of
    common?

    In general, I think DR could have been a little more generous
    with bank pointers in their tables.  You still need too much common
    if you are making a full system and have loads of tables to deal with.


2]  The manual also says that a DRVTBL entry must be zero if the drive
    does not exist.  Could I just fill in all 16 entries with the DPH
    addresses and have SELDSK return HL=0000 (as it normally would)
    if the drive doesn't exist?  I'd like to set up all of the fixed
    tables in the BIOS ahead of time so that the system is easily
    and interactively expandable.  Total flexibility is our theme for this
    project.



                       2B or D4,

                       Jonathan Platt  (JWP@MIT-MC)