The Evolution of CICS

The Evolution of CICS: The Language and Terminal Feature (1970)

Terminal devices which were popular in the mid- and late-1960s were of the so-called start/stop variety. Various teletype machines were available from AT&T, such as the 83B3 or the TWX/33/35. A teletype machine basically had a keyboard/printer and possibly a 'torn paper tape' punch and reader. IBM introduced the IBM 1050 in the mid-1960s and it also included a keyboard/printer and paper tape punch and readers.

When CICS was first announced in 1968/69, its support of terminals included not only the 1050 and teletype terminals, but also the IBM 2740, which was similar to the 1050 in that it was basically a keyboard/printer (typewriter-like device). CICS also supported one of the first commerically available graphics devices, the IBM 2260/65. All of these devices used the start/stop communication protocol, where the data to be sent or receive was bounded by control characters.

In May of 1970, IBM announced that CICS would be enhanced to support additional terminal types, plus, the very significant announcement of support for COBOL and PL/I as application programming languages for use with CICS. This support became available in December 1970.

The new terminal support being added by the so-called Language and Terminal Feature included the IBM 1030 Data Collection System, the IBM 2741 (another keyboard/printer/typewriter-like device), dial support for the 1050/2740/2741 and support for binary synchronous devices such as the IBM 2780, S/360 and IBM 1130. The binary synchronous (bisync) (BSC) protocol was significantly different than the start/stop protocol. Device support added to CICS over the years was driven both by IBM marketing new device types as well as customers having those devices and wanting to use them with CICS. The 2780 was a (relatively) high speed printer and customers wanted higher print speeds than were available with start/stop devices.

The IBM 2260/65 was fairly popular in the late 1960s and programming the device was basically on a display line by line. The 2260 could be attached locally to the computer or be used on remote communication lines (leased lines, initially, and then later dial-up support was added).

In 1972, the IBM 3270 was introduced and immediately supported by CICS. The 3270 was in marked contrast to the line by line orientaion of the 2260. The 3270 had a very powerful command set, enabling the user to display data at any point on the screen, as well as controlling the display attributes (intensify, blink, reverse video, display dark, etc). The initial CICS support for the 3270 enabled the customer to program 3270 data streams natively or to use the higher level programming facilities of CICS' Basic Mapping Support (BMS).

Initially, CICS Development did not think COBOL or PL/I were appropriate for the high volume, quick response objectives for an online system. But customers pressed IBM to support the high level languages. CPU and storage usage was one consideration for attempting to use COBOL and PL/I within CICS, but the more serious concern was that neither language (at the time) produced reusable/reentrant code. CICS found it necessary to dynamically allocate unique copies of working storage (for instance, the Task and Program Global Table (TGT, PGT) for COBOL) so as to permit more than one transaction to use an application at one time.