Operating Systems

VM and the VM community have proved to be survivors; a tough journey has made VM and its users stronger.

Every five to 10 years, some threat to VM arises in the form of poor economic conditions, marketing pitches in the guise of new technologies, or some eager, young executive within IBM who has come up with the brilliant idea of saving money by getting rid of VM. Rather than capitulate to these threats, the response of the VM community has been to rise up and prevent disaster. It’s a battle that has produced a lot of scars but has resulted in the robust hypervisor and ecosystem we call z/VM today

This article reviews how VM has survived and even prospered over the years. It’s an incomplete, though hopefully interesting, retrospective. For a more comprehensive analysis, please see Melinda Varian’s work “VM and the VM Community: Past, Present and Future,” which is available at www.leeandmelindavarian.com/Melinda/neuvm.pdf.

The Golden Years: Early ’80s

Back in 1981, VM/370 gave way to VM/SP Release 1, EDGAR deferred to XEDIT, and VM found itself in a golden age of sorts. The “Doubtful Decade,” as the SHARE VM Group had labeled it, had passed. SHARE attendances were measured in the thousands, and the future looked rosy. Hardware-wise, we were about to see the introduction of the 43xx series of processors, which were more like an oversized piece of furniture than their room-filling predecessors. Microcode— Extended Control Program Support (ECPS)—was created specifically to meet the needs of VM and VSE users.

In 1983, VM/SP Release 3 (see Figure 1) became available, and with it Restructured Extended Executor (REXX), a vitally important development that remains relevant today. REXX prompted dramatic growth in the number and types of utilities and applications running on CMS. With the announcement of SQL/DS (see Figure 2), VM/CMS was primed to act as a base for developing and running sophisticated applications. When the RXSQL program offering became available in 1986, the programming power of REXX and the data management of SQL/DS were coupled to provide a sophisticated, powerful tool base.


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