BOOTING CP/M ON THE C128 FROM DEVICES 9, 10 OR 11

                     by Ismael Cordeiro (ismael@cam.org)


As you should have already  noticed,  CP/M on the C128 only boots from device
8. I decided to  find a way of making it  boot from device 9 because I have a
1571 as device 8 and a 1581 as  device 9 and when I boot CP/M  many files are
automatically copied to drive M. Booting from a 1581 saves me 25 seconds.

With a 1541/1571 boot disk the only way  to change the device CP/M boots from
is by changing the CP/M boot routines in ROM and burning new EPROMs. However,
with a 1581 boot disk you can easily make CP/M boot from devices 9, 10 or 11.
Of course this only works with the 28 May 87 version of the C128 CP/M because
it's the only one supporting the 1581. It also works with  Simeon Cran's ZPM3
installed. Maybe it won't work with modified  versions of the C128 CP/M, like
BIOSR4, BIOSR6, etc., because of address changes but I haven't checked it.


- Format a CP/M 3.5 DISK and copy CPM+.SYS and CCP.COM to it.

- Using a CP/M disk editor (ZAP, EDFILE, FU, etc.)  change the bytes below in
  CPM+.SYS. The addresses and sectors (or records) below assume that the file
  starts at address 000 and that the first  sector  (or  record)  is 0. If in
  your disk editor the file starts at  address 100 and/or the first sector is
  1 you'll have to add 100h to the addresses and/or 1 to the sector numbers.

  Address  Sector  Byte

  0E6E      1C      01    (01=device 8, 02=device 9, 03=device 10,
                           04=device 11)
  112F      22      00    (00=device 8, 01=device 9, 02=device 10,
                           03=device 11)

  Don't forget to write the changes to the disk!

- Go to native mode and with a sector editor change the bytes below.

  Track   Sector   Position   Byte

   40       5        45         8    (device number: 8, 9, 10, 11)
   40       8       117         8    (device number: 8, 9, 10, 11)

  To be sure that the byte is the right  one, check the sequence 169 15 162 8
  (A9 0F A2 08 in hexadecimal) on both sectors. The byte to be changed is the
  8 at the  end  of  the  sequence.  Don't forget to write the changes to the
  disk!

- Put the disk on the device you chose  and  enter  BOOTUx  (x  is the device
  number).


I  would  like  to  thank  Myklos  Garamszeghy  for his excellent articles in
Transactor and Randy Winchester for clues that led me to the right path.