Title   : Tutorial on using the 1541 job queue

    read this carefully it may save a disk some day. i'm about to tell you
a secret about the 1541 that you may have heard about before in some of
those inside dos books. as you might already know the 1541 is composed of 3
parts theres the code for a hi level comand interpreter which knows what to
do for commands i,s,r and a few others. then theres level 2 which knows how
to read,write,extend and poison files. level 2 and level 3 have many bugs
in them most of which cause poison disks. a simple way to see this is to
scratch more then 3 files in a row and then try a save&replace. now try to
read the most recent file written to the disk before the scratches and it
will have had a few of its sectors over written by the s&r file. the same
thing will occur with a few other of the level 3 s,r commands.

   a little note to young hackers

     All of you 5 year old's out there remember, next time you write an
operating system to be careful and write lots of little modules that can be
tes ted and debuged instead of 16k of jumping around in mainline,irq and
nmi monster routines which never seam to end, but instead just run on into
something else.

     level 1 will be the most useful to any one contiplating writing an
improved operating system. it's the monster code which reads and writes
sectors to disk memory. in the stuff i've read it's been called the job
que. the job que is how the dos reads sectors. it simply puts a comand
followed by the track and sector into the job que memeory and off goes the
drive. job que memory is composed of 3 bytes per memeory buffer. yes there
more that one place to read sectors into. In fact there are 5 sector
buffers in the drive heres the break down

        job que            buffer
     0000 command         0300-03ff
       01 command         0400-04ff
       02 command         0500-05ff
       03 command         0600-06ff
       04 command         0700-07ff
       05 i havent used it it
       06 track           0300-03ff
       07 sector
       08 track           0400-04ff
       09 sector
       0a track           0500-05ff
       0b sector
       0c track           0600-06ff
       0d sector
       0e track           0700-07ff
       0f sector

 with this you can read and write sectors using only the m-r and m-w
commands i'll upload a program in a few day's which will be the bios of my
new os  it will contain the routines to read and write sector an a heck of
alot more when i feel like using all the features of the routines i
wrote.i'll also give the specifics of how to use all of it. i've used all
of these thing's in my forth system and they sure do work. one last thing
the only secondary thats used is 15 and due to the way things work it never
has to be opened. you can just tell it to talk and listen. finally if any
of this intrigues you let me know i'm going to need all the people i can
get to test the "public domain operating system one" which i will
distribute as freeware. Since thats the only way I figure it might gain
acceptance.



                                            bye for now
      irwin r. shapiro

                                     as this is freeware if you feel it is
helpful or it fills a void between what you have and what you want let me
know and send  donation if possible. you can reach me via the following:
this sig. compuserve mailbox 73145,130  . western union easylink telex II
9103338689 (irssi)  . western union easylink mailbox 62803073 or simply my
mailing address. irwin r. shapiro, psc 1 box 8189, homestead, fl 33039 . .