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Concept
Shared Variables
Summary
Shared Variables are a feature of the programming language APL which allows APL programs running on one processor to share information with another processor. Although originally developed for mainframe computers, Shared Variables were also used in personal computer implementations of APL. Shared Variables could be used to control peripheral devices, or to communicate with external files, database management systems, or other users. Shared Variables were first introduced by International Business Machines Corporation (IBM) in their APL.SV software product in 1973, and are still available , in APLs from IBM and Dyalog, for the operating systems Linux and Windows.
When APL\360 was first introduced in 1968, there were no built-in means by which a user could directly access data from outside of the APL system. Thus, starting in 1969, IBM developed the shared variable facility. Following APL.SV, the IBM VS APL and APL2 program products also supported shared variables, as did the IBM 5100 line of computers.
Shared Variable Processors were available to allow APL access to the following:
Standard operating system files (TSIO)
Time Sharing Option (TSO) and Conversational Monitor System (CMS) command processors (AP100)
VSAPL Stack Processor (AP101)
VSAPL Session Manager (AP102)
CMS Native Files (AP110)
CMS and TSO Native Files (AP111)
APL2 Data File Processor (AP121)
Virtual storage access method (VSAM) Files (AP123)
Full Screen Display Manager (AP124)
IBM Graphical Data Display Manager (GDDM) (AP126)
IBM Db2 (AP127)
In the early 1980s, I. P. Sharp Associates, which offered a rich and advanced APL, introduced Shared Variables in their product. Many of the Shared Variable Processors available for IBM products were also written for Sharp APL, notably TSIO (called PJAM), AP124, AP126, and AP127. Further, as I. P. Sharp also offered IPSANET which allowed in-house clients of SHARP APL to be connected to the network, a Network Shared Variable Processor (NSVP) allowed programs from one mainframe site to access another.
Official source
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