VSAM (Virtual Storage Access Method) is both a dataset type and an access method for managing various types of datasets. When used as an access method, VSAM offers greater functionality with greater performance and flexibility than other disk access methods. In VSAM, records are maintained in a unique format that is not understandable by other methods. VSAM organizes data as files on Mainframe computers. This is one of the most common high-performance file access methods used in different versions of operating systems such as MVS, z/OS, and OS/390. With VSAM, enterprises can organize records in a file in physical order (the order they were entered) or logical order using a key (for example, the employee ID number) or based on their relative record numbers on DASD (Direct Access Storage Device). Record lengths can be fixed or variable in VSAM.
