The job queue is the vital link between the two controllers. Jobs are initiated on
the file side by providing the disk controller with sector header and type of
operation information. The disk controller seeks the optimum job and attempts
execution. An error condition is then returned in place of the job command. If
the job is unsuccessful, the file side re-enters the job a given number of times,
depending upon the operation, before generating an error message.
The secondary address given in the OPEN statement is used by DOS as the
channel number. The number the user assigns to a channel is only a reference
number that is used to access the work areas, and is not related to the DOS
ordering of channels. The LOAD and SAVE statements transmit secondary
addresses of 0 and 1, respectively. The DOS automatically interprets these
secondary addresses as LOAD and SAVE functions. Unless these functions are
desired when opening files, avoid secondary addresses of 0 and 1. The remaining
numbers, 2 through 14, may be used as secondary addresses to open up to five
channels for data. Secondary address 15 is used to access the command channel
for error messages, INPUT and GET statements and for "memory" commands.
DISK UTILITY COMMAND SET
The disk utility command set consists of the following commands:
Commands Abbreviations General Format
BLOCK-READ B-R "B-R:"ch;dr;t;s
BLOCK-WRITE B-W "B-W:"ch;dr;t;s
BLOCK-EXECUTIVE B-E "B-E:"ch;dr;t;s
BUFFER-POINTER B-P "B-P:"ch;p
BLOCK-ALLOCATE B-A "B-A:"dr;t;s
BLOCK-FREE B-F "B-F:"dr;t;s
memory-write M-W "M-W"adl/adh/nc/data
memory-read M-R "M-R"adl/adh
memory-execute M-E "M-E"adl/adh
USER U "Ui:parms"
Where: ch = the channel number in DOS: identical to the secondary address
in the associated OPEN statement.
dr = the drive number: 0
t = the track number: 1 through 35
p = the pointer position for the buffer pointer.
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