Date   : Wed, 13 May 1992 19:04:04 GMT
From   : ditka!unixhub!falcon.SLAC.Stanford.EDU!ralph@decwrl.dec.com (Ralph Becker-Szendy)
Subject: Re: Master drive

In article <1992May13.170335.16878@noose.ecn.purdue.edu> 
wieland@ea.ecn.purdue.edu (Jeffrey J Wieland) writes (edited):
... about the question why CP/M always logs in drive A after resetting the
    system ...
>Actually, CP/M 2.2 logs in drive A because it needs to read
>the CCP (and possibly BDOS) from the boot tracks.  
No. There are two different things here: Warm-boot and logging in. The
warm-boot (reading CCP, BDOS and perhaps even the BIOS from the boot
track) are done internally to the BIOS. If you have source to your
BIOS (or if you wrote it yourself), you can modify such that it
warmboots from any other drive (for example in my system, I can set
the boot disk to any disk in the system, frequently I set it to drive
C). Second, the BDOS will "log in" (read and decode the directory,
build the ALV) a drive whenever you start it (which is usually after
each warm-boot, although newer BDOS replacements can bypass this with
a fast relog option). Even though I am warmbooting from drive C, the
BDOS will still log in drive A. Now it gets even crazier: Assume I am
booting from drive C, and my current working drive is B (I have set
the current drive at address 0004h to "B" within the startup code for
example). The BDOS will still log in drive A after each warmboot! The
annoying thing is that even though I never need drive A I still have
to have a functional and readable drive connected there.

Lesson: Warmbooting is done internally to your BIOS. You may or may
not be able to tell your BIOS to boot from a drive other than A.  You
have a current working disk, stored at location 0004h. The BDOS will
always log in drive A when being started.

>Perhaps
>a better way to handle it would be to modify your BIOS so
>that you can change the physical to logical drive mapping.
>Then, assuming that you can sysgen the RAM disk, you could
>have a startup EX or ZEX script that would sysgen your RAM
>disk and remap it as drive A.
That's the way to do it. If you don't like drive A being accessed
all the time, declare your favorite drive to be A instead.

-- 
Ralph Becker-Szendy                          RALPH@SLACVM.SLAC.STANFORD.EDU
Stanford Linear Accelerator Center                      RALPH@SLACVM.BITNET
M.S. 95, P.O. Box 4349, Stanford, CA 94309                    (415)926-2701
My opinion. This is not SLAC, Stanford U, or the US DoE speaking. Just me.