IBM System 360 User Manual page 59

The compiler, linkage editor, loader. and your own program require
data sets in order to operate. In an operating system without TSO these
data sets are defined with data definition (DO) JCL statements. In TSO,
these data sets are defined through the EDIT and ALLOCATE commands. You
can use the EDIT command to define and create input data sets. You can
use the ALLOCATE command to define output and work data sets and
libraries, and to allocate the data sets you created with the EDIT
command. This section discusses the ALLOCATE command.
Note: Compilers that have prompters associated with them will allocate
data sets for you. Your installation can tell you if these Program
Product facilities are available to you. The data sets for the linkage
editor and loader are allocated for you by the LINK and LOADGO commands,
respectively. You need only allocate them if you invoke the linkage
editor or the loader with the CALL command.
The number of data sets you need is determined by the program
(compiler., linkage editor, loader, or your own program) you are going to
use. (The publications associated with the IBM-supplied programs list
the data set requirements.) The number of data sets you can allocate
depends on the number of data sets assigned to you in your LOGON
procedure. The LOGON procedure defines a series of data sets. Some of
th~se
data sets are fully defined and correspond to data sets that you
always need in your processing. The remaining data sets are left
undefin.ed; they are defined when you define a data set with an ALLOCATE
or EDIT command.
When you define a data set with the ALLOCATE command, it remains
allocated until you use the FREE command to free the data set
definition. (The FREE command is described in ftFreeing an Allocated
Data set. ft )
When ,l"'Ju create a data set with the EDIT command, the system uses one
of the undefined data sets in the LOGON procedure to define the data
set. When you save the data set and end the EDIT command, the system
saves the data set, enters its name in the system catalog.. and frees the
definition in the LOGON procedure for further use. When you again use
the EDIT command to make changes to the saved data set, the system finds
the data set through the system catalog and uses another Of the
available definitions to define the data set. When you end the EDIT
command, the system frees the data set definition. If you want the data
set to remain allocated in your LOGON procedure. you must use the
ALLOCATE command.
You can list the data sets allocated to you with the LISTALC command
(described in ftListing the Names of Your Data Setsft). The system lets
you know., as part of the LISTALC listing, how many DO statements are
available for allocation. For example, if there are five available data
sets you get the following message:
5 DATA SETS CAN BE ALLOCATED DYNAMICALLY
You can allocate as many data sets as there are available
definitions. If you need more data sets you can free a previously
allocated data set with the FREE command (described in ftFreeing an
Allocated Data setft). After you free a data set .. you can use the
available definition to allocate another data set with the ALLOCATE
command .•
If you have to allocate the same data sets every time you log on, you
can have your installation allocate them in the form of fully defined
data sets in the LOGON procedure or you can build a procedure containing
your ALLOCATE statements and execute that procedure as soon as you are
logged on.. (See section on "Writing Command Procedures ft. ) In either
case you do not have to type the same ALLOCATE commands every time you
log on,.
Entering and Manipulating Data 59