STARTING A JOB STREAM
After preparing job streams and placing them in the DOS/VS card reader, the message READY FOR COMMUNICATIONS appearse Enter a null line (with the return or enter key) to cause an interruption. This interruption
causes DOS/VS to begin reading from the card reader.
If the LOG command was entered before beginning the job stream, DOS/VS cn the user's terminal all the job control statements
that are executed.
As the DOS/VS operator
8 the virtual machine user can enter control
statements directly from the terminal. For example: To execute
cataloged prcgrams or procedures, enter the ASSGN, DLBL, and EXEC statements necessary to execute the program directly from the console. WHEN A JOB IS FINISHED When the DOS/VS virtual machine running a single partition finishes
reading a spool file (which may contain one or more jobs), it posts this
attention message to indicate that the reader is empty: 1COOA ATTN. OOC If additional jcbs are in the card reader and were spooled as separate CP spool files, enter a null line to cause DOS/VS to begin reading from the card reader. If no more files are in the reader and the user
enters a null line, this message appears to indicate that operator
intervention is required: OP08A INTERV REQ SYSRDR=OOC If desired, users can put cards into the real system card reader to
direct ancther job stream to the DOS/VS virtual machine. When the DOS/VS virtual machine receives cards in its reader, it begins reading
them automatically.
If the card reader of the DOS/VS virtual machine is spooled with the
CaNT cperand, then any jobs received in the card reader while a job is
executing are read upon completion of the current job stream. If a job
stream and if the end of the spool file is reached before
another job is received, an interruption must be issued to cause the
next job to be read.
Tc terminate the DOS/VS terminal session, use the attention key (or
equivalent) to enter the CP command environment. Under CP, either enter
the LOGOFF command to log off the V8/370 system or use the IFL command to load another operating system into the virtual machine. COMMUNICATING WITH CP While operating the DOS/VS virtual machine, use CP commands to: • Ccmmunicate with the system operator or other virtual machine users • Query the status of virtual machine devices or spool files • Attach cr detach devices from the virtual machine configuation
section 3. DOS/VS in a Virtual Machine 91

To enter a CP command while the DOS/VS virtual machine is in operation, press the attention key (or its equivalent) twice, quickly,
to force a CP read. After entering the necessary CP commands, use the CP BEGIN cemmand to resume DOS/VS virtual machine execution. For example: If a DOS/VS PAUSE control statement requests the VM/370 cFerator tc Ferform some action, the user must enter the CP environment
to send a message to the VM/370 system operator. The following lines
represent a typical sequence on a typewriter terminal:
// PAUSE ASK OPERATOR TO ATTACH TAPE AS 284
! ! CP msg op please attach scratch tape as 284
sleep TAPE 284 ATTACHED CP begin
The SLEEP command locks the keyboard and places the virtual machine in a
dormant status to wait for any messages,. When the message appears
indicating the tape is attached, press the attention key once to return
to CP, and then issue the BEGIN command to resume virtual machine
execution. Because the // PAUSE message is still outstanding, press the RETURN key to continue DOS/VS execution.
In most cases during virtual machine operation, use the 'CP function to
enter CP commands directly from the virtual machine environment. Users de not always have to press the attention key (or its equivalent) to
enter the CP environment. For example: If the virtual machine is
waiting for a read, a user can enter a CP command with the ICP function: #cp msg op please mount vo1240
The command line is processed by VM/370, and the virtual machine is
still waiting for a read. This method may be convenient for entering CP commands.
Note: At times CP commands cannot be entered with the ICP function. For exiiple: During the IPL procedure when DOS/VS is processing 1FL commands, the CCis used for these reads expect only three bytes of
data. Any additienal information on CP command lines is truncated. While DOS/VS is running in the virtual machine, a user can interrupt its
execution by using the attention key (or its equivalent) on the
terminal. When this key is pressed, the DOS/VS attention handler
responds with these messages:
AR 1I60A READY FOR COMMUNICATIONS. AR When these messages appear, a user can enter attention commands. To
resume program execution, enter a null line. Normally, wait until the
attention has been processed before signaling another one. An exception
would be when canceling a dump.
92 IBM VM/370 Operating Systems in a Virtual Machine