4P bootable NEWDOS/80
The Model 4P
versions of NEWDOS/80 have a special MODELA/III
ROM image file that allows them to boot on the
Model 4P. The 4P versions will boot on a Model
III, 4 or 4P system.
file is the standard TRSDOS v6.xx file that has
been padded and placed on the NEWDOS/80 disk so
it aligns with LDOS's six sector/granule
structure. The file also has 3 sectors of a LDOS
DIR/SYS embedded in it so that it aligns with a
real track boundary.
The 3rd byte of
sector 1 on track 0 (boot sector) has been
modified to point to the embedded LDOS directory
in the MODELA/III file. This byte is not used by
NEWDOS/80 since it uses the 3rd byte of sector 0
to find the directory lump. During a Model 4P
boot this byte is used to find the directory
track of an LDOS disk, search for the MODELA/III
file entry and then load the MODELA/III file.
Pointing the 3rd byte at the embedded LDOS
directory allows the 4P to find the MODELA/III
file and load it.
The 4P version of
NEWDOS/80 can be used almost exactly like the
regular version of NEWDOS/80, but because of the
exact placement of the MODELA/III file on the 4P
disk and the 1 byte modification of the boot
sector certain guidelines must be obeyed or the
original disk or its copies will be unbootable on
a Model 4P.
MODELA/III cannot be modified, deleted,
moved or recopied onto the NEWDOS/80 4P
disk. Doing so will result in the disk
being only Model 3/4 bootable.
MODELA/III files on the single &
double sided 4P disks are not the same
and because of the padding and embedded
LDOS directory are not compatible with
other DOSs. However, the actual ROM image
that is loaded, is.
To make a
4P bootable copy use a type 5 copy using
the BDU option, example:
You can use this method to make a real
Model 4P boot disk in a
compatible PC drive.
the 4P NEWDOS/80 disk to a disk of a
different configuration by using a type 6
copy will result in the disk being only
Model 3/4 bootable.