Architecture: VSAM

div class="separator text-center"> Every time a CICS transaction reads an account record, there is a file somewhere holding that record. It is not a relational table. It is not a flat file. It is a VSAM dataset: a structured, indexed file that CICS reads in under 10 milliseconds, keyed precisely on the account number, without scanning from the beginning. VSAM is the file system that mainframe application programs live on. Every C… Read More

Explained: COBOL

Every time a bank processes a payment, there is a reasonable chance a COBOL program is doing the work. Every time an insurance company calculates a premium or a government agency processes a benefit, there is a good chance COBOL is involved. The language was designed in 1959. It is still running, unchanged in many cases, in production today. Most engineers have heard of COBOL and formed an opinion of it without ever reading a line of it. The repu… Read More

Architecture: CICS

A bank teller presses Enter. Within 30 milliseconds, the customer's account balance is on the screen. Somewhere in a data center, a COBOL program ran, read a VSAM file, formatted a response, and terminated. The same thing happened simultaneously for several thousand other tellers at other terminals in other branches. None of them waited for each other. None of them interfered with each other's data. That is CICS. It has been doing exactly… Read More