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VSE (operating system)

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Developer21st Century Software (previously IBM)
OS familyDOS/360 and successors
Working stateCurrent
Source modelClosed source
Latest release6.3 / May 17, 2022; 2 years ago (2022-05-17)[1]
Marketing targetIBM mainframe computers
Official website21cs.com/vsen/

VSEn (Virtual Storage Extended) is an operating system for IBM mainframe computers, the latest one in the DOS/360 lineage, which originated in 1965. It is less common than z/OS and is mostly used on smaller machines.[2][3][4]

DOS/VSE was introduced in 1979 as a successor to DOS/VS; in turn, DOS/VSE was succeeded by VSE/SP version 1 in 1983, and VSE/SP version 2 in 1985.[5] In the late 1980s, there was a widespread perception among VSE customers that IBM was planning to discontinue VSE and migrate its customers to MVS instead, although IBM relented and agreed to continue to produce new versions of VSE.[6][7] In February 2005, IBM announced z/VSE as successor to VSE/ESA 2.7, which was named to reflect the new System z branding for IBM's mainframe product line.[8][9] In June 2021, 21st Century Software Inc announced that it had licensed the z/VSE source code from IBM with the intention of developing new versions of the operating system.[10] As part of this transfer, z/VSE was renamed to VSEn.[1]


DOS/360 originally used 24-bit addressing. As the underlying hardware evolved, VSE/ESA acquired 31-bit addressing capability.[11]

IBM released z/VSE Version 4, which requires 64-bit z/Architecture hardware and can use 64-bit real mode addressing, in 2007. With z/VSE 5.1 (available since 2011)[11] z/VSE introduced 64-bit virtual addressing and memory objects (chunks of virtual storage), that are allocated above 2 GB.

User interfaces[edit]

Job Control Language (JCL)[edit]

A Job Control Language (JCL) that continues in the positional-parameter orientation of earlier DOS systems is VSEn's batch processing primary user interface.[12][13] There is also another, special interface for system console operators.[14]

Beyond batch[edit]

VSEn, like z/OS systems, had traditionally provided 3270 terminal user interfaces. However, most VSEn installations have at least begun to add Web browser access to VSEn applications. VSEn's TCP/IP is a separately priced option for historic reasons, and is available in two different versions from two vendors. Both vendors provide a full function TCP/IP stack with applications, such as telnet and FTP. One TCP/IP stack provides IPv4 communication only, the other IPv4 and IPv6 communication. In addition to the commercially available TCP/IP stacks for VSEn, IBM also provides the Linux Fastpath method which uses IUCV socket or Hipersockets connections to communicate with a Linux guest, also running on the mainframe.

Using this method the VSEn system is able to fully exploit the native Linux TCP/IP stack.[15]

IBM recommends[16] that z/VSE customers run Linux on IBM Z alongside, on the same physical system, to provide another 64-bit application environment that can access and extend z/VSE applications and data via Hipersockets using a wide variety of middleware. CICS, one of the most popular enterprise transaction processing systems, is extremely popular among VSEn users and now implements recent innovations such as Web services. Db2 is also available and popular[clarification needed].

Device support[edit]

VSEn can use ECKD, FBA and SCSI devices. Fibre Channel access to SCSI storage devices was initially available on z/VSE 3.1 on a limited basis (including on IBM's Enterprise Storage Server (ESS), IBM System Storage DS8000, DS6000 series), but the limitations disappeared with 4.2 (thus including IBM Storwize V7000, V5000, V3700 and V9000).[17]

See also[edit]


  1. ^ a b Lisa Klemens (2022-03-25). "21st Century Software Announces VSEn V6.3". Retrieved 2022-06-09.
  2. ^ Axel Buecker; Boudhayan Chakrabarty; Lennie Dymoke-Bradshaw (2016). Reduce Risk and Improve Security on IBM Mainframes (Volume 1). ISBN 978-0738440101. Extended (z/VSE) is popular with users of smaller mainframe computers.
  3. ^ "Ahead of the Pack". IBM Systems Magazine. At the risk of oversimplification, z/VSE is similar to z/OS but relatively smaller, simpler ... cost-effective
  4. ^ Stedman, Craig (29 Jan 1996). "IBM teaches VM, VSE new mainframe tricks". Computerworld. 30 (5): 39.
  5. ^ Jim Hoskins; Bob Frank (2003). Exploring IBM Eserver Zseries and S/390 Servers: See Why IBM's Redesigned Mainframe Server Family Has Become More Popular Than Ever. Maximum Press. p. 275. ISBN 978-1-885068-91-0.
  6. ^ Cortese, Amy (21 Aug 1989). "Militant VSE users upbeat but impatient". Computerworld. 23 (34): 17.
  7. ^ Ambrosio, Johanna (23 Jul 1990). "VSE gets jumpstart with sequel". Computerworld. 24 (30): 6.
  8. ^ "IBM z/VSE V3.1 generally available". IBM. February 1, 2005. z/VSE continues the focus on interoperability that began with VSE/ESA Version 2 Release 5, and continued with VSE/ESA Version 2 Release 6 and VSE/ESA Version 2 Release 7
  9. ^ Roger Kay (January 13, 2015). "With Z Systems Refresh, IBM Reminds Us That Mainframes Remain Relevant". Forbes. The new system — called IBM z13 and running the fastest ... this latest revision of IBM's time-hallowed product line incorporates new ... fast enough to intervene in time to avert brand damage and lost sales? Well ... What used to be "System z" is now "z Systems," with the current product being the IBM z13.
  10. ^ Rebecca Levesque (2021-06-01). "21st Century Software Technologies, Inc. Enters Agreement to License z/VSE Operating System and Middleware Stack From IBM". 21st Century Software. Retrieved 2022-06-09.
  11. ^ a b Ingolf Salm (May 7, 2012). "Virtual Addressing With z/VSE: From 24-Bit to 64-Bit". EnterpriseSystemsMedia.com.
  12. ^ "Introduction to the New Mainframe: IBM z/VSE Basics" (PDF). March 1, 2016.
  13. ^ "Storage Considerations For the Batch External Interface".
  14. ^ "Hints and Tips for z/VSE 5.2" (PDF).
  15. ^ "The z/VSE Fast Path to Linux on System z". Archived from the original on 2013-10-22. Retrieved 2013-10-16.
  16. ^ "z/VSE Fast Path to Linux on IBM Z" (PDF). Both z/VSE and Linux on IBM Z run as z/VM Guests in the same z/VM-mode LPAR .... The use of a z/VM-mode LPAR is recommended.
  17. ^ "z/VSE SCSI Support and Migration Options" (PDF).

External links[edit]