Sanity Check: A Virtualization Primer for IT Execs

by Bill Carico
February 12, 2009

The terms logical and virtual are virtually synonymous. For example, on the mainframe a Logical Partition (LPAR) is the virtualization of physical processor and memory resources that ultimately allows multiple operating systems to run on the same machine. LPARs were essentially derived by taking a subset of the Virtual Machine (VM) operating system, which provides software partitioning of resources, and puts this functionality in hardware microcode for better performance.

The predecessor to z/OS is MVS, which stands for Multiple Virtual Storage. MVS excelled at running mixed workloads by allowing each application or subsystem to have its own virtual address space. This remains one of the pillars of the mainframe’s renowned bulletproof security design. It also introduced the notion of horizontal scalability, since the range of a system’s potential addressing capacity (range of memory addresses) is assigned for each address space. By the way, each address space shares the operating system, which resides in common virtual memory.

The mainframe hardware has been expanded over the decades. IBM has effectively put virtualization on steroids, adding features for high-speed, inter-address space communication and allowing data-only virtual spaces and hyperspaces.

When comparing platforms, all virtualization hasn’t been created equally, and an underpowered environment will get bogged down. The mainframe has added extensive hardware assist during its 40 years of refinement to turbo-charge hypervisors, which in turn facilitate “virtual guests” in ways that are well-beyond the industry’s “next best.” And because IBM owns the entire stack (hardware and software), it will be hard for any other provider to come up with a tighter knit technology.