z/Virtual Storage Extended (z/VSE™) is popular with users of smaller mainframe computers. Some of these customers eventually migrate to z/OS® when they grow beyond the capabilities of z/VSE.

Compared to z/OS, the z/VSE operating system provides a smaller, less complex base for batch processing and transaction processing. The design and management structure of z/VSE is excellent for running routine production workloads consisting of multiple batch jobs (running in parallel) and extensive, traditional transaction processing. In practice, most z/VSE users also have the z/VM® operating system and use this as a general terminal interface for z/VSE application development and system management.

z/VSE was originally known as Disk Operating System (DOS), and was the first disk-based operating system introduced for the System/360™ mainframe computers. DOS was seen as a temporary measure until OS/360 would be ready. However, some mainframe customers liked its simplicity (and small size) and decided to remain with it after OS/360 became available. DOS became known as DOS/VS (when it started using virtual storage), then VSE/SP and later VSE/ESA™, and most recently z/VSE. The name VSE is often used collectively to refer to any of the more recent versions.