ALLOCATE command

Use the ALLOCATE command or the ALLOCATE subcommand of EDIT (the subcommand's function and syntax are identical to the ALLOCATE command) to allocate dynamically the VSAM and non-VSAM data sets, and UNIX files required by a program that you intend to execute. Each UNIX file system data set contains zero or more UNIX files.

Each UNIX file system data set has a 44-byte data set name and must be capitalized and cataloged. A UNIX file has a mixed-case name of up to 250 characters.

There is no documented API for an UNIX file system data set. Users can access UNIX files with BSAM, QSAM, VSAM and UNIX calls.

You can specify data set attributes for non-VSAM data sets that you intend to allocate dynamically in several ways:

Use the LIKE operand to obtain the attributes from an existing model data set (a data set that must be cataloged) whose data set attributes you want to use. You can override model data set attributes by explicitly specifying the desired attributes on the ALLOCATE command.
Identify a data set and describe its attributes explicitly on the ALLOCATE command.
Use the ATTRIB command to build a list of attributes. During the remainder of your terminal session, you can have the system refer to this list for data set attributes by specifying the USING operand when you enter the ALLOCATE command. The ALLOCATE command converts the attributes into the data control block (DCB) operands for data sets being allocated. If you code DCB attributes in an attribute-list and you refer to the attribute-list using the USING operand on the ALLOCATE command, any DCB attribute you code on the ALLOCATE command is ignored.
With the Storage Management Subsystem (SMS) installed and active, use the DATACLAS operand. Your storage administrator might provide default data set attributes through the automatic class selection (ACS) routine. Using DATACLAS to define the data class for the data set makes specifying all the attributes unnecessary.

In this book, "with SMS" indicates that SMS is installed and is active. "Without SMS" indicates that SMS is not installed. Requesting space, in terms of a quantity of logical records, is device-independent and is particularly useful in conjunction with a system-determined BLKSIZE. This space can be obtained by omitting the BLKSIZE operand and coding LRECL, RECFM, and DSORG, or acquiring these from SMS DATACLAS.