Section 5. Operator Spooling Functions Spooling Input and output files for use and access by virtual machines through
unit record devices are maintained by CP as disk data files using a mechanism called spooling. Individual files can be identified and
manipulated using various console functions. The disk records are
chained to form a logical file from dynamically assigned areas on
specially formatted CP disk areas. Data records from disk are read into
available page space obtained through the CP paging mechanism. The data
records contain the actual data to be used and the CCWs to properly
control the format. These CCWs are directly executed to perform the
actual unit record oFerations on the real hardware. CP can support any number of virtual and real unit record devices given sufficient system resources.
The data is placed in the spool buffers through the virtual machine
unit record simulation routines in CP. Certain spool files have a
special data format (system dumps, for example) and are accessed using a
special interface. SPOOLING CONSIDERATIONS VM/310 spooling facilities allow several virtual machines to share one
or more unit record devices. Since virtual machines controlled by CMS ordinarily have modest requirements for unit record I/O, such device
sharing is quite advantageous, and it is the standard mode of system operation.
Each user has, as a general rule, a virtual reader, a virtual punch,
and a virtual printer as his spooling devices; In addition, the virtual
console can also be classified as a spool file generator as all input
and output to the console can be logged on a sFool file. This console
log, and the files created by the user's virtual spooling devices, can
be processed by the real unit record devices that attach to the system. CP controls and schedules the operation of the real unit record
devices via spooling techniques. Virtual machine SIO instructions
directed to those unit record devices designated as spool devices in the
user directory entry are intercepted and '.odified by CP. CP generates
another I/O operation, transparent to the virtual machine, which
replaces the one specified. The new operation is directed to a CP spooling disk area which acts as intermediate storage between the real
unit record device and the virtual machine. The data transfer operation
between a spooled unit record device and the virtual machine is, in
reality, between a CP spool file and the virtual machine. spool file
records are page size (that is, 4096 byte blocks), and are transferred
between storage media via the CP paging mechanism. Section 5. Operator Spooling Functions 209

SPOOLING FUNCTIONS CP spooling support performs the following five functions for virtual
aachines:
1. It siaulates, with software routines, the operation of the virtual
unit record devices that are attached to each user's virtual
machine. The simulation makes it appear that the program in the
virtual machine controls real unit record devices. Unit record
device simulation involves the interception and interpretation of
user Start I/O (SIO) instructions, the movement of data to and from the user's virtual storage space, and the reflection of
interruption codes and ending conditions in the virtual machine.
2. It operates the real unit record equipment attached to the real machine. Spooling moves print-image and punch-card-image files to
a real printer and card punch, and creates spool files froa data
read in fro. the real card reader.
3. It provides an easy-to-use interface between the machine users, the system operator, and the spooling system to allow
flexible and easy switching of system resources between many users. A set of general user and operator commands can request these
functions.
4. It allows keyed-in CP machine console input
or in addition to,
initiate or terminate
terminal session. commands and responses as well as virtual
and output to be placed on disk instead of,
being displayed at the terminal. You can
virtual console spooling at any time during a
5. It provides the ability telefrccessing network.
to spool files across the RSCS Spooling commands can be separated by type into those that affect
virtual devices, those that affect real devices, and those that affect
queued spool files within the system. The commands that affect virtual
devices are available to all general users; a user may affect the status
of devices that attach to only his virtual machine. For a discussion of
the Class G spooling commands, see VBL.Jl.Q £R £2!.!s!lg Only the spooling or resource operator can use commands that affect
the status of the real spooling devices. Commands affecting the user's
virtual machine closed spool files that are awaiting processing are
available to all users, with some additional capabilities available to
the spooling operator. For eXaaFle, a user can alter characteristics of
only those files that have the same userid as his, but the spooling
operator can change the status of any spool file in the system. The "CP Commands" section of this publication describes these commands. You can create input spool files (that is, data available at a
specific user's virtual card reader), when you flace cards in the real card reader that are preceded by a special V!/370 card that identifies the virtual machine userid of the user requesting spool files. When the virtual machine operating system writes to a virtual printer
or card punch, it output spool files and stores thea on direct
access devices. Real output is scheduled for a real printer or card
punch, or for reaote output, whenever a user logs off the system or
issues a CP spooling co.mand to close the file. 210 VB/370 Operator's Guide