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Reinventing the Dual-Boot Wheel

"Virtualization" is the latest in a long line of buzzwords which refer to old technology just reaching the PC world.

VM (stands for Virtual Machine) is an IBM mainframe operating system which has been in use since at least the 1970s. It has its own user "shell" called CMS, but it was primarily designed as a control program to run multiple guest operating systems.

In the 1980s, IBM created Processor Storage Management/Logical Partitioning (PR/SM). PR/SM is essential the hardware microcode implementation of VM.

Understand that the virtual machines have virtual CPUs which are mapped arbitrarily to the real CPUs. There may be many more virtual CPUs than actual, physical CPUs.

Now, who would want to run multiple guests on the same box? How about software developers who need to support multiple OS releases? How about data centers migrating from DOS/VSE to MVS/XA? All your CPU, memory and peripherals are available to programs running under all guest operating systems running under VM. On the PC, anybody who benefitted from dual-boot technology can now have the advantages of running multiple OSes without having to shut one down and start another. On the mainframe, we used to run MVS in one PR/SM LPAR and UTS (Amdahl Unix variant) on the other. You can benchmark different CPU configurations easily without having to buy multiple boxes, etc.

New interest in VM has emerged recently. VM/CMS virtual machines now run "on the metal" in mainframe logical partitions. Many, many virtual Linuxes can be run under VM. Some folks in the field have been able to boot as many as 10,000 Linux virtual machines under VM on the mainframe.

To me, this just underscores the status of Linux as an amateur science project, but that's not the point. Other advantages of running under VM or PR/SM are multiplying virtual memory areas and reducing the overhead of multiple processors on a single system image. How about continuous availability? You can shut down, service and IPL (boot) a system in one partition while another remains active running your critical business apps. (You do have critical business apps, don't you?)

One last comment: Believe it or not, while PCs cannot be logically partitioned (until this latest AMD announcement), VM can be installed on a PC like IBM's P390 series. There are even versions of z/OS (IBMs current generation of MVS) which run under Windows. One free-ware version is Hercules 3.8. These are serious, industrial-strength operating systems, and I would strongly recommend learning something about them, since three quarters of the world's data resides on mainframes.

It helps to have mastered the old wheel before trying to master the new wheel.

Posted by: RimaDog@...   Posted on: 03/30/05 You are currently: a Guest | Members login | Terms of Use

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