When one attempts to define what constitutes an Operating System, most definitions tend to center around the fact than an OS manages various hardware resources (CPU, memory, I/O paths, I/O devices) and provides various logical resources and functions useful for running applications.
Perhaps a more generic way of viewing a typical Operating System is that it creates the illusion of a virtual machine that is better suited as an application platform - an environment in which many of the complexities of dealing with I/O, resource sharing, security, integrity, etc. at the actual hardware level are are resolved by the Operating System and hidden from and can be largely taken for granted by application programmers. VM is usually regarded as a "control program" rather than an "Operating System" precisely because it passes on to the the virtual machines running under it all the complexity of the actual hardware, including access to and the risks associated with privileged instructions. While VM does make some enhancements available to the virtual machines, primarily to support the CMS environment in a virtual machine and to provide controls for the virtual machines themselves; a generic Operating System running under VM uses very little beyond the host hardware instructions. VM is cool and can be a very useful tool, but trying to implement a complex multi-user application with shared data using bare VM virtual machines with just the functions provided by VM shows why many would hesitate to classify it along with other Operating Systems, much less consider it the only "true" operating system. On 02/19/2010 07:10 PM, George Henke wrote: ... > I have since come to realize that even though MVS is more robust with more > functionality, that when all is said and done, VM is really the only "true" > operating system, because it is the only operating system that can run other > operating systems. In effect reducing MVS to the level of a CICS. ... -- Joel C. Ewing, Fort Smith, AR [email protected] ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
