In the world of mainframe operating systems, z/VSE is often overshadowed by better-known siblings such as z/OS. But z/VSE has an impressive story worth telling.
Virtual Storage Extended (z/VSE) is an operating system designed specifically for IBM mainframes. It was first introduced in the 1960s and has continued to evolve. It is known for its stability, reliability, and efficiency in handling large amounts of data and complex transaction processing.
z/VSE is proof that even older technologies, if well-maintained and developed, can remain relevant in the modern IT landscape.
In the early days of the mainframe era, z/VSE was one of the leading operating systems, especially in commercial environments. It provided a robust platform for mission-critical applications and supported a wide variety of programming languages and database management systems. These features made it a preferred choice for organizations that needed a reliable and powerful IT infrastructure.
In addition, z/VSE offers comprehensive security features to protect sensitive data and control system access. It also supports modern technologies and standards, such as TCP/IP for network communications and Web services, to facilitate integration into heterogeneous IT environments.
Today, z/VSE(VSEn) is still relevant, especially for organizations that rely on proven and stable mainframe technologies. It is widely used in mainframe environments of all sizes, where its efficiency and reliability are impressive. Many of these organizations use z/VSE(VSEn) for mission-critical applications that require high availability and security, such as in the financial, retail, and logistics sectors.
z/VSE remains popular with many customers, especially small and medium-sized businesses. These customers value z/VSE for mission-critical applications and transaction processing.
A key reason for the continued relevance of z/VSE(VSEn) is its ability to integrate modern technologies while protecting investments in existing IT infrastructures. For example, it supports virtualization and can run with Linux on the same mainframe, enabling flexible and cost-effective use of hardware. It also offers extensive support for Web services and modern communication protocols, making it easy to integrate into today’s IT landscapes.
History of z/VSE
1964: IBM introduced the System/360, a family of compatible computers that became the basis for many later developments. The original operating system for the small and mid-sized models was the Disk Operating System (DOS/360). This system allowed data to be managed on hard disks and was a significant step away from tape-based systems.
1970s: DOS/360 evolved into DOS/VS (Virtual Storage), which allowed virtual storage. This was a significant advance because it greatly increased system efficiency and performance. Virtual memory made it possible to run programs larger than the physically available memory by loading parts of the program into memory as needed.
1980s: DOS/VS evolved into DOS/VSE, which offered additional features and enhancements. During this time, IBM also began introducing VSE/SP (System Product), which offered improved system management and security. VSE/SP allowed for more efficient use of system resources and provided enhanced security features to better control access to sensitive data.
1990s: The next major development was VSE/ESA (Enterprise Systems Architecture), which introduced support for larger memory addresses and improved networking capabilities. VSE/ESA enabled the use of 31-bit addresses, which improved memory management and performance. It also supported advanced networking protocols that allowed better integration into distributed networks.
2000s: IBM introduced z/VSE, designed specifically for the z/Series mainframes. This version supported the z/Architecture and enabled 64-bit addressing, significantly increasing memory and system performance.
2007: With the release of z/VSE version 4, support for 64-bit real addressing was introduced. This enabled even more efficient use of available memory and improved overall system performance.
2014: z/VSE version 5.2 was released, further improving system performance and security. This version supported advanced encryption technologies and provided enhanced networking capabilities to meet the increasing demands for data security and integrity.
2017: Version z/VSE 6.2 was released. This release included numerous enhancements and new features to meet today’s needs. These include support for TLS 1.3 for secure network communications and enhanced virtualization capabilities.
2021: IBM transferred the development and distribution of z/VSE to the U.S. company 21st Century Software (21CS). This transfer marked a significant turning point in the operating system’s history, as it is now developed under the new name VSEn. VSEn 6.3, the first release under 21st Century Software, brought additional improvements in security, memory management, and networking capabilities.
Initially, DOS/360 was seen as a temporary solution until the more complex OS/360 was ready. However, many customers appreciated the simplicity and efficiency of DOS/360 and stuck with it even after OS/360 became available. Over the following decades, it evolved and underwent several transformations, as noted above. Each version brought improvements and new features such as virtual memory support, enhanced security features, and improved networking capabilities.
“z/VSE is a fascinating example of the durability and adaptability of mainframe technologies.”
IBM tried several times to replace z/VSE with the more powerful and complex z/OS. z/OS offers greater functionality and is designed for larger and more demanding mainframe environments. However, z/VSE has remained popular with many customers, especially small and medium-sized businesses (SMBs). These customers value z/VSE for their mission-critical applications and transaction processing.
There is a loyal and dedicated z/VSE user base, especially in the DACH region (Germany, Austria, Switzerland). Many of these companies have invested in their z/VSE infrastructures for decades and continue to use the operating system for their core applications.
The story of z/VSE shows how, despite many attempts to replace it with (supposedly) more modern alternatives, an operating system remains relevant because of its unique advantages and the loyalty of its users. It is a fascinating example of the durability and adaptability of mainframe technologies.
VSEn and the future
The first version of the operating system developed by 21CS was released in May 2022 under the name VSEn V6.3. This version was designed to be fully compatible with IBM z/VSE 6.2 to make the upgrade as transparent as possible for users. VSEn V6.3 brought many improvements and new features to meet today’s needs:
- One of the most important developments under 21CS was the integration of cloud technologies. This innovation allows users to run z/VSE applications in hybrid cloud environments and take advantage of the benefits of the cloud. These include the flexibility and scalability that cloud solutions offer and the ability to use resources more efficiently.
- VSEn can be virtualized under z/VM – in parallel with Linux or z/OS. This simplifies infrastructure, reduces costs, and increases flexibility. VSEn can also be seamlessly integrated into modern REST or Web services architectures via middleware such as the VSE Connector or OLTP Web Support, which is ideal for hybrid cloud environments.
- Another focus has been on improving security. New security features have been introduced to ensure the protection of sensitive data and to meet the requirements of modern IT security standards. These include enhanced encryption technologies and support for Quantum-safe Encryption, which provides future-proof security mechanisms. Encrypted connections also benefit from hardware acceleration through the CPACF and Crypto Express adapters.
- The networking capabilities of z/VSE have also been enhanced to enable seamless integration into modern and hybrid IT infrastructures. This includes support for new protocols and improved network performance, increasing the efficiency and reliability of communications.
21CS has partnered with many different technology companies to advance the development of z/VSE and provide users with access to a wider range of tools and services. Customer support has been expanded to help users migrate to new versions of z/VSE and ensure they get the most out of the latest features and enhancements.
In addition, 21CS is committed to the continued development of z/VSE to meet the changing needs of the IT world. The focus is on integrating new technologies such as artificial intelligence and machine learning to make z/VSE even more powerful and versatile.
z/VSE and IBM z17
The introduction of IBM z17 in April 2025 brings the latest technology and significant performance, security, and future-proofing benefits to established platforms such as z/VSE. CPU-intensive or I/O-heavy VSEn workloads will benefit from faster processors, optimized caches, and advanced I/O systems. Single-threaded jobs will also run noticeably faster.
New machine instructions and a planned COBOL update will further improve efficiency. In addition, Data Processing Units (DPUs) offload the CPU to provide significantly enhanced I/O throughput – ideal for batch and OLTP (CICS) workloads.
In addition, 21CS is committed to continually evolving VSEn to meet the changing needs of the IT world. The focus is on integrating new technologies such as artificial intelligence and machine learning to make VSEn increasingly powerful and versatile.
Conclusion
z/VSE may not have the same name recognition as z/OS, which is often considered the quintessential mainframe operating system. Still, it is a robust and reliable operating system that plays an important role in many organizations around the world.
It is proof that even older technologies, if well-maintained and developed, can maintain their place in the modern IT landscape.
