Model 4P bootable NEWDOS/80

Note from Dave Keil (who created this image)

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.

The MODELA/III 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.

The 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.

The 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:
COPY 0,1,,BDU
You can use this method to make a real Model 4P boot disk in a compatible PC drive.

Copying 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.
