VSAM

VSAM (Virtual Storage Access Method) is a filesystem technology used in IBM mainframes.

VSAM is not a filesystem per se, it is a layer which sits on top of the IBM VTOC filesystem.

JCL (Job Control Language) is used to control access to such systems.

Links

 * Wikipedia article
 * VSAM tutorial (actually a bunch of code samples)
 * Defining a Data Set with JCL
 * VSAM demystified