The Evolution of CICS

The Evolution of CICS: CICS - State of the Art (1979)

Preface: With each new version and release of the Customer Information Control System (CICS), the product introduced support of new or improved technologies. When reviewing the evolution of CICS, one has to remember the date of the product enhancement, and then consider the nature of the enhancement and why it was important at the time. This article examines the CICS "State of the Art" relevant in 1979.

Although CICS/VS 1.4.1 was the latest product release to be delivered in 1979, the announcement of CICS/VS 1.5, to be delivered in 1980, created a high level of expectation among CICS users. CICS/VS 1.4 introduced Intersystem Communication (ISC) and the ability of CICS systems (OS and/or DOS) to interact with each other using VTAM. Applications on one CICS system could cause "function shipping" of a request to another ISC-connected system, accessing remote data or initiating remote transactions.

CICS/VS 1.5 was announced to provide Multi-Region Operation (MRO) by which multiple regions in CICS/OS/VS or partitions in CICS/DOS/VS could intercommunicate. The term "transaction routing" was now added to the CICS vocabulary. MRO enabled the user to distribute the CICS workload across multiple CICS regions, providing benefits such as virtual storage constraint relief (VSCR), better multiprocessor utilization or simply separation of test and production systems. Customers became anxious awaiting delivery of 1.5 planned for 1980.

CICS/VS 1.4.1 was a "modification release". That is, it did not contain a large number of significant enhancements but was shipped as Modification 1 of Version 1 Release 4, hence the product numbering of "1.4.1" CICS/VS 1.4.1 contained support for newer devices such as the IBM 6670 Information Distributor, and support for dynamic open/close of the VTAM ACB (access control block). For the DOS user, support of Fixed Block Architecture (FBA) devices was important, complementing the already available technology for Count/Key/Data (CKD) devices. CICS/OS/VS 1.4.1 added CICS support of field level sensitivity for accessing DL/I data bases.

Object level compatibility gained greater importance in the late 1970s, with CICS assurances that command level application programs need not be recompiled when migrating from one CICS release to another. Object level compatibility was a major benefit of the CICS command level interface introduced with CICS/VS 1.3 and enhanced in 1.4. Applications using the command level API were no longer sensitive to any changes in the internals of CICS. The benefit to both CICS and the user was that CICS could change its internals to improve itself or provide new function to the user, without impacting existing user command level applications.

In November 1979, IBM announced additional new Intersystem Communications function to be delivered in 1980 with CICS/VS 1.5. CICS/VS 1.4 gave customers the ability to connect CICS/OS/VS and/or CICS/DOS/VS systems and using function shipping access remote file or database data or initiate remote transactions. CICS/VS 1.5 would enhance ISC to now include CICS-IMS intersystem communication, using VTAM/SNA LU6.1 protocols.

Support of Advanced Program to Program Communication (APPC) using LU6.2 protocols was to come later. The notable difference between LU6.1 and LU6.2 had to do with the non-synchronous nature of LU6.1 versus the synchronous nature of LU6.2. Until IMS added its support of APPC, it was exclusively a message queued system. That is, a message was received and then asynchronously an IMS transaction was initiated, or taking an output example, an application may queue a message to go to CICS, but that did not occur until the IMS transaction ended. In any case, CICS to IMS intersystem communication was favorably received by customers having both transaction managers within their enterprise.

1979 would be characterized as a year of steady growth for CICS and its introduction of new or improved technologies.