ARPAVAX:C70:info-cpm (09/10/82)
>From UCBARPA:dag Thu Sep 9 23:58:49 1982
Received: from UCBARPA.BERKELEY.ARPA by UCBVAX.BERKELEY.ARPA (3.196 [9/8/82]) id a11794;
9-Sep-82 18:18:58-PDT (Thu)
To: info-cpm at BRL
Via: Ucb-C70; 9 Sep 82 23:05-EDT
Via: Brl; 9 Sep 82 23:15-EDT
Via: Brl-Bmd; 9 Sep 82 23:27-EDT
Some interesting observations and just a little raving:
For the past few weeks, I have been trying to write a program
that will take a 2k, properly orged image and place it on
track 0, CCP sectors. That's not all that difficult. What's
difficult is trying to make it run on machine to machine.
But, sayest thou, CP/M is "the software buss". Thou repeatest with,
all you need is to get information on the disk parameters and use
that.
WRONGO, MAN WITH FLAT FINGERS....Argh!!!
CP/M will allow you to get back a disk parameter header and
thereby a pointer to the disk parameter block through the SELDSK
bios call. Well, the disk parameter block (DPB) describes the disk,
right? Uh uh, no way Jose. The DPB describes MOST of the disk,
however, HOWEVER, many manufacturers tend to make track 0
different from other tracks. They make other tracks double
density, but track 0 single density, or vice versa, or with
cheese on top. Nevertheless, they make track 0 with different
parameters than the rest of the disk. The SELDSK DPB does
not necessarily describe track 0. But, you say, doesn't
SYSGEN know how to access track zero. I mean, it DOES
access track zippo. Ah well, you see OEM's purchase an OEM
license for CP/M and get the source for SYSGEN.
AND THEN THEY MODIFY THE THING, OR REWRITE IT.
See, I thought, well, maybe, just maybe, I could check the
parameters in SYSGEN to see what track zilch is made of, you
know, sugar and spice and everything nice. Well, I could,
on about 50% of the systems out. Another 50% have totally
rewritten SYSGEN. Well, I could patch MOVCPM, thought your
perilous writer. But noooOOOOOooooOOOOOo....more than 50%
of the OEM's diddle with MOVCPM, or don't even include it.
So it's like this...if you modify track zero stuff, beware...
you will not be able to make it thoroughly portable.
I spoke to Digital Research about this, and they know about
it, but can't do a whole lot.
Argh...<<growl>>...Argh!!!!
(End Rave)
Thank you for listening, this time until next time.
David
DAG at UCB-ARPA