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3.4.6.1.1 The Default UNIT Operand Value

 






   If the ALLOCATE command is used without UNIT operand, the default UNIT 
   operand value depends on whether the ALLOCATE command is executed in the 
   foreground or in the background. 





   Processing in the Foreground:  The ALLOCATE command uses the default UNIT 
   operand value from the protected step control block (PSCB). 



   During LOGON processing this value is taken from either the user attribute 
   data set SYS1.UADS or the security system being used (if SYS1.UADS is not 
   being used) and put in the PSCB (PSCBGPNM field). See the ACCOUNT command 
   and its UNIT operand in OS/390 TSO/E System Programming Command Reference 
   on how to specify a default device type in SYS1.UADS. 





   Processing in the Background:  If the Terminal Monitor Program (TMP) 
   IKJEFT01 (or IKJEFT1A or IKJEFT1B) is executed in the background and the 
   ALLOCATE command without UNIT operand is issued, the default value from 
   the PSCB is nulls, because LOGON is not executed. 





   Search Order for UNIT Operand Value:  The UNIT operand value is searched 
   for in the following sequence: 






    


  1.         The catalog for this data set, provided the VOLUME operand of the 
       ALLOCATE command is not being used. 


    

  2.         The protected step control block (PSCB). 


    

  3.         The UNIT keyword on the ALLOCxx member of SYS1.PARMLIB. 


    
       If there is a UNIT keyword, and Storage Management Subsystem (SMS) is 
       installed and active and has a default UNIT in the SMS control data 
       set (SCDS), the latter one is used instead. 


    

  4.         The MVS system default SYSALLDA, which contains all DASD defined to 
       the system. 







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