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Basic Disk Operating System (BDOS) Functions
4-22
with the appropriate attributes set or reset. It is the user's responsibility to insure
that the file name is not ambiguous. Function 30 searches the default disk drive
directory area for directory entries belonging to the current user number that match
the FCB-specified name and type fields. All matching directory entries are updated
to contain the selected indicators. Indicators fl' though f4' are not presently used,
but may be useful for applications programs, since they are not involved in the
matching process during file open and close operations. Indicators f5' through f8'
are reserved for future system expansion. The currently assigned attributes are
defined as follows.
t1':
The R/O attribute indicates whether or not the file is in read/only
status. The BDOS will not issue write commands to files in R/O status.
t2':
The System attribute is referenced by the CP/M DIR utility. If the
attribute is set, DIR will not display the file in a directory display. The
DIRS command, however, will display the file.
t3':
The Archive attribute is reserved but not actually used by CP /M-86. If
it is set, it indicates that the file has been written to back-up storage by
a user-written archive program. To implement this facility, the archive
program sets this attribute when it copies a file to back-up storage.
Any programs updating or creating files must reset the attribute.
Further, the archive program backs up only those files that have the
Archive attribute reset. Thus, an automatic back-up facility restricted
to modified files can be easily implemented.
Register AL returns OFFH (255 decimal) if the referenced file could not be found,
otherwise zero is returned.
GET DISK PARAMETER BLOCK ADDRESS
ENTRY
CL: 1FH
FUNCTION 31
GET ADDR
(DISK PARMS)
RETURN
BX: DPB Offset
ES: Segment Base
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