System Generation (OS)

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This article is about System Generation in OS/360 . For System generation in DOS/360, see System Generation (DOS) . For other uses, see System generation.
Operating System/360
Developer IBM
OS family OS/360 and successors
Latest release 21.8
Available in Algol 60, Assembler (E), Assembler (F), CLIST, COBOL (E, F and U), FORTRAN (E, G and H), PL/I (F), RPG
Platforms S/360, S/370
Kernel type N/A
License none
Succeeded by OS/VS1, OS/VS2 (SVS), OS/VS2 (MVS), MVS/SE, MVS/SP Version 1, MVS/XA, MVS/ESA, OS/390, z/OS
Operating System/Virtual Storage 2 (Single Virtual Storage)
Developer IBM
OS family OS/360 and successors
Latest release Release 1.7
Available in Assembler (XF), CLIST
Platforms S/370
License none
Preceded by OS/360
Succeeded by OS/VS2 (MVS), MVS/SE, MVS/SP Version 1, MVS/XA, MVS/ESA, OS/390, z/OS

System Generation (SysGen) is a two-stage process for installing or updating OS/360,[1][2] OS/VS1, OS/VS2 (SVS), OS/VS2 (MVS) and chargeable systems derived from them.[3][4][5][6][7] There are similar processes for, e.g., DOS/360, which this article does not cover. Also, some of the details have changed between releases of OS/360 and many details do not carry over to later systems.

There are several reasons that IBM provided a system generation process rather than simply providing a mechanism to restore the system from tape to disk. System/360 did not have self-identifying I/O devices, and the customer could request installation of I/O devices at arbitrary addresses. As a result, IBM had to provide a mechanism for the cutomer to define the I/O configuration to OS/360. Also, OS/360 supported several different options; IBM needed a way for the customer to select the code appropriate for the options needed at a particular installation.

The SysGen process runs as a series of jobs under the control of the operating system. For new installations, IBM provides a complete pre-configured driver system, which is intended only for preparing for and running the sysgen, not for production use.

Prior to running the Sysgen, the customer must initialize a set of distribution volumes and restore a set of distribution libraries from tape to those volumes. These libraries include data that the sysgen process will copy to target libraries, input to utilities used by the sysgen process, macro definitions used by the sysgen process and load modules that the sysgen process will include when linking load modules into target libraries.

Stage 1 is the compilation of a sequence of assembler macro instructions describing the configuration to be installed or updated. The assembler does not actually compile any object code, but instead compiles a series of PUNCH pseudo-ops in order to generate a job stream for Stage 2. As IBM changed the nomenclature for OS/360 options, it also changed the Sysgen macro definitions to use newer names for the options.

The TYPE keyword on the CTRLPROG macro in the Stage 1 input specifies the type of control program. By Release 13 the old terms SSS, MSS and MPS had been replaced by PCP, MFT and MVT. The later M65MP type is a variation of MVT.

The SCHEDULER macro in the Stage 1 input specifies the type of scheduler; Release 13 still used the values SEQUENTIAL and PRIORITY, but those were subsequently replaced by the values used for the TYPE keyword on the CTRLPROG macro.

These types are

Primary Control Program (Option 1)
Multiprogramming with a Fixed number of Tasks (MFT)[8][9][10] (Option 2)
Multiprogramming with a Variable number of Tasks (MVT)[11] (Option 4)
Model 65 Multi-Processing, a special case of MVT.

The GENERATE macro in the Sysgen input can be any of several types:

  • Full generation of the operating system.
  • Generation of compilers and associated libraries.
  • Updating of the I/O configuration

For MVT (either TYPE=MVT or TYPE=M65MP) with TSO, the TSOGEN macro plays the same role as GENERATE. Either macros analyzes the options specified on the previous macro calls and punches the Stage 2 job stream.

The Stage 2 jobstream uses a variety of utilities, including the assembler and linkage editor.

This process is now obsolete; it was initially[12] replaced by the use of SMP/E, IOCP[13] and MVSCP,[14][15][16] then later by SMP/E and HCD.[17][18]

See also[edit]


  1. ^ IBM (November 1966). IBM System/360 Operating System Introduction. C28-6534-1. 
  2. ^ IBM (June 1971). IBM System/360 Operating System Introduction OS Release 21. Fourth Edition. GC28-6534-3. 
  3. ^ IBM (August 1967). IBM System/360 Operating System System Generation Release 13. Fourth Edition. C28-6554-3. 
  4. ^ IBM (August 1974). IBM System/360 Operating System System Generation Release 21.8. Fourteenth Edition. GC28-6554-13. 
  5. ^ IBM (September 1972). OS/VS System Generation Introduction VS1 Release 1 VS2 Release 1. Second Edition. GC26-3790-1. 
  6. ^ IBM (March 1973). OS/VS2 System Generation Reference VS2 Release 1 (PDF). Second Edition. GC26-3792-1. 
  7. ^ IBM (January 1979). OS/VS2 System Programming Library: System Generation Reference Release 3.8. Eighth Edition. GC26-3792-7. 
  8. ^ IBM (October 1966). IBM System/360 Operating System Multiprogramming With a Fixed Number of Tasks (MFT) Concepts and Considerations. First Edition. GC27-6926-0. 
  9. ^ IBM (October 1967). Planning for Multiprogramming With a Fixed Number of Tasks Version II (MFT II). First Edition. C27-6939-0. 
  10. ^ IBM (March 1972). IBM System/360 Operating System: MFT Guide OS Release 21.7. Eleventh Edition. C27-6939-10. 
  11. ^ IBM (March 1972). IBM System/3S0 Operating System MVT Guide OS Release 21. Fifth Edition. GC28-6720-4. 
  12. ^ In stages, e.g., DFP V2 added MVSCP (see GC28-1615) but did not eliminate the sysgen process.
  13. ^ IBM. Input/Output Configuration Program User's Guide and ESCON Channel-to-Channel Reference. GC38-0401-00. 
  14. ^ IBM (May 1987). MVS/Extended Architecture Data Facility Product General Information. Fifth Edition. p. 17. GC26-4142-4. 
  15. ^ IBM (June 1987). MVS/Extended Architecture Data Facility Product Planning Guide. Third Edition. p. 18. GC26-4147-2. 
  16. ^ IBM. MVS Configuration Program. GC28-1615. 
  17. ^ IBM. z/OS Hardware Configuration Definition Planning. GA22-7525-13. 
  18. ^ IBM. Hardware Configuration Definition: Using the Dialog. GC33-6457. 

External links[edit]