Attached Support Processor
| Industry | Computer software |
|---|---|
| Founded | March 1967 |
| Products | Loosely coupled multiprocessing system within OS/360 |
| Parent | IBM |
Attached Support Processor (ASP) represented IBM's approach to loosely coupled multiprocessing within the OS/360 environment. The company subsequently rebranded it as Asymmetrical multiProcessor while retaining the ASP abbreviation.
The origin of ASP traces back to the 7094/7044 direct-coupled configuration, which utilized data channel-to-channel communication. Integrating an IBM 7044 as a peripheral processor more than doubled the throughput capacity of the 7094.
Launched in March 1967, ASP initially linked two System/360 machines through a channel-to-channel adapter (CTCA). A typical ASP setup comprised a primary System/360 mainframe—such as Model 50, 65, or 75—operating OS/360, paired with a smaller support processor, generally Model 40 or higher. The support processor ran the ASP supervisor under OS/360 PCP (Primary Control Program). Its responsibilities included managing printing, card reading, and punching tasks, thus allowing the mainframe to concentrate on application processing. In basic configurations, it could queue approximately 30 jobs, dispatching them according to priority and preparing removable I/O devices such as disks and tapes for the main processor.
The mainframe was set up similarly to an independent OS/360 system except that the CTCA replaced conventional I/O hardware. The support processor typically featured at least a Model 40 G (with 128KB of memory), two selector channels, an 1052 console typewriter, a 2540 card reader/punch, an 1403 printer, and three 2311 disk drives. Access to an 2400-series tape drive was recommended for optimal performance.
To accommodate emulator jobs, the main processor’s OS was adapted to overlay itself with the 7090/94 emulator temporarily before reverting to OS/360 for mixed workload processing. This overlay method became unnecessary with the integrated emulation features introduced in the Model 85 and later in the System/370.
Subsequent improvements enabled a single support processor to oversee multiple mainframes and introduced Local ASP (LASP), where one processor could operate as both local and main. These capabilities were incorporated into ASP version 3, which also added compatibility with OS/VS2 (SVS).
With the introduction of MVS on System/370, IBM redesigned ASP and renamed it Job Entry Subsystem 3 (JES3), a system still operational as of 2015.