J28-6169, 04.01.02

The text read off it

[04.01.02]

The sequence of operations within the framework is:

The Basic Monitor is called into core from the system tape. For the first job, this is done by the initial start procedure; for subsequent jobs, this is done by a routine in the Nucleus upon return from the processor which handled the previous jobs.
The Monitor functions as directed by control cards. For example, the sequence (the exact format of the control cards will be specified later)
```
$ATTACH          A6
$AS              SYSPP1
```
would result in an entry in the Unit Function table of the Nucleus, assigning physical unit A6 to the function of System Peripheral Punch tape until changed by some subsequent assignment. It should be emphasized that such an assignment is needed only to deviate from the normal one in use at a particular installation.

Finally, upon recognition of
```
$EXECUTE         Processor-name
```
(Processor-name = CT for Commercial Translator), the Basic Monitor will position the System Library tape to the named processor, read in the first record, and relinquish control to it.
The processor involved examines the Unit Function and Unit Availability tables within the Nucleus; and from them determines which I/O units to use for the job. It then proceeds to process the current job.
When the processor encounters the control card $IBSYS, the availability table is restored (if necessary) and control is turned back to the Basic Monitor.
Steps 1 through 4 are repeated until the stack of jobs has been completely processed.

The Unit Function and Availability Tables

In order to achieve the maximum flexibility in the use of I/O units attached to the machine, it is necessary to know the number and status of these units at all times. For this purpose, the nucleus contains an assembled table, the Unit Availability table, which describes the physical configuration of the machine, the number of channels, and the number and type of units on each channel. Programs operating within the system use this table to make their unit assignments,