Commodore Plus 4 - Page 345

The Disk Drive 333
where the diskname is a string of up to 16 characters that is displayed whenever a
directory of the disk is requested. The disknameis a literal string (in quotes) or a
string expression (in parentheses). The identification is two characters that the
DOS uses to identify the disk. It is a good idea to give a different identification to
each disk. For a brand new disk, an identification must be given, but an old disk
can be cleared of information more quickly by omitting the identification
parameter. The drive number is required (for the 1541, use 0). The unit number,
which is optional, is the device number for the disk drive. It is set by the factory to
8. The device number can be changed in the hardware according to instructions in
the disk drive manual. The device number can also be changed temporarily by the
disk address change utility program on the diskette that comes with the drive.
Whenever the device number is optional in a command, it is assumed to be 8 if
omitted.
To format a diskette by direct command to the DOS, use
PRIWT#
where filenumber is the logical file number of the previously opened command
channel, diskname is the name (up to 16 characters) to be displayed with the
directory of the diskette and identification is the two characters used by DOS to
identify the diskette. As with the header command, any information previously
on the diskette is lost. You can reformat a reused disk more quickly by omitting
the identification.
Initializing a Diskette
The DOS keeps its own local copy of the diskette's ID and BAM (block availabil
ity map). It uses the BAM information to decide what areas of the diskette are
available for writing. If DOS discovers that a diskette it is attempting to write on
has a different ID from that it has stored, an error (error number 29) occurs.
Unfortunately, the DOS identifies diskettes on the basis of their ID number only.
If two diskettes have the same ID number, and they have been switched since the
DOS last updated its information, the DOS uses an incorrect BAM. This is a
disastrous occurrence. You can easily avoid this by ensuring that the DOS has the
correct BAM in memory. This is done with the initialize command that is sent
through the command channel:
PRINT* filenumber/'I"
where filenumber is the logical file number of the previously opened command
channel. It is a good idea to perform an initialization whenever you switch
diskettes, regardless of their respective ID numbers.