Attached Support Processor

Attached Support Processor (ASP) is an implementation of loosely coupled multiprocessing for IBM's OS/360 operating system.^[1]^[2] IBM later changed the name to Asymmetrical multiProcessor but retained the acronym ASP.

History

ASP evolved from the design of the 7094/7044 direct coupled system, using data channel to data channel communication. By attaching an IBM 7044 as a peripheral processor throughput of the 7094 was more than doubled.

ASP was introduced in March 1967, and initially allowed connection of two System/360 computers via a channel-to-channel adapter (CTCA).^[3]

As initially defined an ASP system typically^[a] consisted of a large System/360 computer, a Model 50, 65, or 75 running OS/360, called the main processor, and a smaller System/360, Model 40 or larger, called the support processor, running the ASP supervisor as a single task under OS/360 PCP (Primary Control Program). The support processor performed functions such as printing, card reading and punching, freeing the main processor to run the application workload. It queued jobs, roughly 30 in the basic configuration, and released them to the main processor in priority order, and also did pre-execution setup of removable input/output devices such as disks and tapes on the main processor.^[2]

The main processor was configured identically to a "stand-alone processor operating under OS/360, except that the channel-to-channel adapter replaces the normal system input and output devices." The support processor was a minimum of a Model 40 G (G indicates memory size of 128KB) with two selector channels, a 1052 console typewriter, a 2540 card read/punch, a 1403 printer, and three 2311 disk drives. It was recommended that the support processor have access to one 2400-series tape drive for support.

The OS version on the main processor was modified to be able to overlay itself with the 7090/94 emulator program when an emulator job was to be run, and the emulator program would similarly overlay itself with OS/360 when done, to process emulated 709x jobs intermixed with standard 360 jobs.^[2] This later became unnecessary with the introduction of integrated emulation programs on the Model 85 and System/370

Later IBM allowed a single support processor to control multiple main processors and added support for Local ASP (LASP), in which the same processor serves as both a local and a main. These capabilities are standard in the final ASP version, version 3, as is support for OS/VS2 (SVS).

With the introduction of MVS for System/370 IBM rewrote and renamed ASP as Job Entry Subsystem 3 (JES3) and it is still in use as of 2015.

Features

ASP has several features that either replace features of the underlying OS, are new or are needed for its own housekeeping.

Multifunction monitor (MFM))

The Multifunction monitor (MFM) multiplexes parallel functions under a single Task Control Block (TCB). The functions must use ASP macros rather than similar OS macros.

SPOOL

The term system input (SYSIN) refers to data presented as part of a job. These include

JCL
Data preceded by a DD *
Data preceded by a DD DATA
Data following a JCL statement (implicit DD *)

The term system output (SYSOUT) includes

Messages about the job, including messages written by the running program
Print data written to DD SYSOUT=output class
Punch data written to DD SYSOUT=output class
Jobs submitted to ASP by the running program.

ASP uses a set of SPOOL volumes^[b] to hold ASP control blocks and datasets associated with jobs. ASP mamages the I/O; to the jobs it appears as tape I/O.

ASP stores control blocks, SYSIN and SYSOUT on SPOOL.

CTC links

ASP uses a channel-to-channel adapter (CTC or CTCA) to connect the support processor to each main processor. The installation generates each as a 1052-7 with FEATURE=CTC.

Pseudo CTC links

ASP uses pseudo CTCs when the same processor serves as both a main and support processor. The installation generates each as a 1052-7 with FEATURE=CTC.

Dummy tape CTCs

A job running under ASP sees SYSIN and SYSOUT datasets as tape datasets, but ASP intercepts the I/O done by the access methods. The installation generates each as a The installation generates each as a tape drive with FEATURE=CTC.

Stages

Each job has several stages, each being an ASP support program. The job can use the normal sequence of stages or can request its own. This includes utility functions like card to card copy.

Notes

↑ If a main processor was a 360/65 then ASP could IPL it between OS/360 and the 7090 Emulator.
↑ Technically a set of DASD datasets, but in practice each fills a full volume.

References

↑ "Representative ASP Installation". Computerworld. September 13, 1967. Retrieved February 7, 2013.
1 2 3 IBM Corporation (1967). Catalog of Programs for IBM System/360 August 1967 (PDF).
↑ Pugh, Emerson W.; Johnson, Lyle R.; Palmer, John H. (1991). IBM's 360 and Early 370 Systems. MIT Press. p. 710. ISBN 0262161230.

[4] If a main processor was a 360/65 then ASP could IPL it between OS/360 and the 7090 Emulator.

[5] Technically a set of DASD datasets, but in practice each fills a full volume.

[1] "Representative ASP Installation". Computerworld. September 13, 1967. Retrieved February 7, 2013.

[PgmCat1967-2] 1 2 3 IBM Corporation (1967). Catalog of Programs for IBM System/360 August 1967 (PDF).

[Pugh-3] Pugh, Emerson W.; Johnson, Lyle R.; Palmer, John H. (1991). IBM's 360 and Early 370 Systems. MIT Press. p. 710. ISBN 0262161230.

[1]

[2]

[3]

[a]

[b]

This page was redesigned at the edge.

A page that knows where it met you.