The reserve clause allows the user to specify the 
number of input/output buffers to be allocated at 
run-time for the files.
If the RESERVE clause is omitted, the number 
of buffers at run time is taken from the DD 
statement when running under MVS, or from the TLBL JCL 
statement when running under VSE. 
If none is specified, the system default is taken.
If the file connector referenced by file-name-1 
in the SELECT clause is an external file connector, 
all file control entries in the run unit that reference 
this file connector must have the same value for the 
integer specified in the RESERVE clause.


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