Architecture: DB2 for z/OS

A payment transaction hits the mainframe. It needs to check an account balance, verify a credit limit, write an audit record, and update three tables atomically. All of this happens under a single unit of work, coordinated by a database that has been running at that bank since the 1980s. If any part fails, every change rolls back. If two transactions try to update the same row simultaneously, one waits. If the system crashes mid-transaction, the… Read More

Architecture: VSAM

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 CICS file definition points to a VSAM dataset. Every … 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