VSAM was first released with the IBM® MVS™ operating systems OS/VS1 and OS/VS2 in the early 1970s. It has been the underlying access method for the IBM DB2® software on MVS and OS/390® since the first release. It is also the most common access method for IMS™ databases.
As well as being the core of IBM relational and hierarchical database management systems, VSAM became the preferred choice for CICS® users when support was introduced in 1974.
These functions are limited for programs that access VSAM files natively.