Rymarczyk, still at Big Blue today as an IBM fellow and chief virtualization technologist, recalls using CP-67 software, one of IBM's first attempts at virtualizing mainframe operating systems. CP-67 and its follow-ups launched the virtualization market, giving customers the ability to greatly increase hardware utilization by running many applications at once. The partitioning concepts IBM developed for the mainframe eventually served as inspiration for VMware, which brought virtualization to x86 servers in 1999.

"Back in the mid-60s, everyone was using key punches and submitting batch jobs," Rymarczyk says in a recent interview with Network World. "It was very inefficient and machines were quite expensive."

The problem of implementing a time-sharing system that would let multiple users access the same computer simultaneously was not an easy one to solve. Most engineers were taking traditional batch operating systems and making them more interactive to let multiple users come into the system, but the operating system itself became extremely complex, Rymarczyk explains. IBM's engineering team in Cambridge, Mass., came up with a novel approach that gave each user a virtual machine (VM), with an operating system that doesn't have to be complex because it only has to support one user, he says.

The first stake in the ground was CP-40, an operating system for the System/360 mainframe that IBM's Robert Creasy and Les Comeau started developing in 1964 to create VMs within the mainframe. It was quickly replaced by CP-67, the second version of IBM's hypervisor, which Rymarczyk began using upon joining IBM's Cambridge operations in 1968. The early hypervisor gave each mainframe user what was called a conversational monitor system (CSM), essentially a single-user operating system. The hypervisor provided the resources while the CMS supported the time-sharing capabilities. CP-67 enabled memory sharing across VMs while giving each user his own virtual memory space.

Rymarczyk says he got to know several of the CP-67 developers and describes himself as one of their "guinea pigs." But even in these early days of virtualization, the technology's benefits were clear.