ZiLOG Z80-RIO Operating System User's Manual page 144

OPEN OPEN
3rd byte of area - length of file name. The
open request can do its own assignment,
removing the necessity for two calls to
ZOOS. If this is done, it will override
any assignment done previously. This
supplemental information should look
exactly like the supplemental information
for an assign request. If no assignment
is to be made, however, this byte should
be -1 (OFFH).
4th byte and following - filename if there is
one.
File attributes:
Each file has a 128-byte record referred to as the file
descriptor record. This contains information concerning
the type of file, where it is on the disk, how it is
organized, etc. Only 40 of the 128 bytes are used by
the system, leaving the remainder for possible use by
the user. When a file is created, the organization,
etc., must be specified by the user, either explicitly
or by default. Similarly, when a file is opened, the
information about the organization may be needed by the
program. In order to accomplish both these ends, that
portion of the file descriptor record which may be of
use to the programmer can be passed back and forth. It
is laid out as follows:
1 Type and subtype. There are 4 types of files
recognized by the system. Each is assigned
one of the top four bits of this word. The
bottom four bits are available for user
defined subtypes.
Bit 7 - procedure type files.
Bit 6 - Directory files.
Bit 5 - ASCII files.
Bit 4 - Data files.
The default is ASCII subtype 0 (20B).
2-3 Record count. Number of records in the file.
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