OS/VS1

OS/VS1 (Operating System/Virtual Storage 1) was a single virtual storage operating system developed by IBM for System/370 mainframe computers. It was a successor to OS/MVT (Operating System/Multiprogramming with a Variable Number of Tasks) and aimed to provide virtual storage capabilities with a simpler architecture compared to its counterpart, OS/VS2 (later MVS).

The key feature of OS/VS1 was its implementation of virtual storage, allowing programs to address more memory than was physically available. This was achieved through paging, where portions of a program's address space were stored on disk and brought into real memory only when needed. This significantly increased the amount of work that could be processed concurrently.

OS/VS1 was designed to run with a single virtual address space per user. While OS/VS2 (MVS) offered multiple virtual address spaces, VS1's simpler structure made it easier to implement and manage, appealing to organizations with less complex processing requirements.

The system provided a range of services, including job management, data management, and system utilities. It supported various programming languages, including COBOL, FORTRAN, and Assembler. Job Control Language (JCL) was used to specify job execution parameters and resource requirements.

Over time, OS/VS1 was superseded by MVS and its derivatives, which offered greater scalability, advanced features, and improved performance. While OS/VS1 is no longer in active use, it represents an important milestone in the evolution of mainframe operating systems and the adoption of virtual storage technology.