VSAM basics

In the early 1970s, VSAM (Virtual Sequential Access Method) was introduced by IBM as a collection of three data set organizations — sequential, indexed, and direct-access, together with the access methods and utilities to be used on the large scale IBM operating systems.

The word virtual means only that VSAM was introduced at approximately the same time as the initial IBM virtual storage operating systems OS/VS1 and OS/VS2. Since then VSAM has been continually improved and enhanced.