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The Job Entry Subsystem (JES) is a component of IBM's MVS (OS/VS2 R2 through z/OS) operating systems that receives jobs into the computer system, schedules them for processing, and controls their output processing. There is also a ''JES''〔(The job entry subsystem of OS/VS1, by J. H. Baily, J. A. Howard, and T. J. Szczygielski, IBM Systems Journal, Volume 13 (1974), No 3, Page 253 )〕 in OS/VS1, often referred to as ''JES1''. While MVS/370's immediate predecessor, SVS, retained the spooling facilities of OS/360, most installations used the optional ASP Version 3 or HASP II Version 4. sometimes incorrectly referred to as HASP4; ASP V3 is available for OS/360 and HASP II V4 has been quite easily retrofitted to OS/360, even on systems which did not, and cannot support the System/370 instruction set. In MVS, JES is a task that runs under MVS and provides the necessary functions to get jobs in to, and jobs out of, the MVS operating system, and to control the scheduling of, and, indeed, their execution. It is designed to provide efficient spooling, scheduling, and management facilities for the MVS operating system. By separating job processing into a number of tasks, MVS operates more efficiently. At any point in time, the computer system resources are busy processing the tasks for individual jobs, while other tasks are waiting for those resources to become available. In its most simple view, MVS divides the management of jobs and resources between the JES and the base control program of MVS. In this manner, the JES manages jobs before (i.e., during the reading and scheduling phases) and after the completion of running the program (i.e., the printing, punching and purgeing phases); the base control program manages them during processing, usually without any specific knowledge of JES. There are three job entry subsystems in MVS; Master, JES2 and JES3. The Master subsystem is used during system initialization and for starting system tasks that must run outside of the control of the primary JES; in particular, it is used to start the primary JES. The other two job entry subsystems have very little in common, and in fact jobs written to run on one usually require small Job Control Language changes before they can be run on the other. JES2 (Job Entry Subsystem 2) is descended from the Houston Automatic Spooling Priority〔〔 (HASP) system, developed by the contractor programmers of IBM as self-initiative and eventually owned and supported by IBM for NASA's Houston-based Manned Spaceflight Center, hence the root word in its name, in the mid 1960s. JES3 (Job Entry Subsystem 3) is similarly descended from the Attached Support Processor〔Eventually renamed to Asymmetric Multiprocessing System〕〔 (ASP), which was IBM's initially preferred system for OS/360 "unit record I/O", although JES2's "shared SPOOL" program product (NJE) ultimately displaced JES3 (and even JES2) in many cases. JES3 ''Main Device Setup'' (MDS) has more control over data sets shared between systems than JES2, and JES3 ''Dependent Job Control'' (DJC) has more provisions for scheduling jobs with dependencies on each other than JES2. With the widespread use of sophisticated job scheduling software, DJC has become less important. ==History== OS/360's job input and print queuing had limited operational flexibility and performance. This was addressed by two field-developed packages: ''Houston Automatic Spooling Priority'' (HASP), and ''Attached Support Processor'' (ASP). Source code was provided to IBM customers for both ASP and HASP, and many customers made substantial enhancements to these programs, some of which were incorporated into the official product. Far more installations made use of HASP than ASP, and in contemporary z/OS systems there are many more JES2 installations than JES3. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Job Entry Subsystem 2/3」の詳細全文を読む スポンサード リンク
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