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Introduction to the IBM Mainframe
Physical Resource / System Management
It can be argued that software dependant virtualisation on mainframes began in the late 1960s. In the 1980s, in response to competition,
IBM introduced PR/SM (Physical Resource / System Management), which uses micro-code.
The basic concept of PR/SM is that the mainframe will be divided into a number of Logical Partitions (LPARs) with each LPAR having access
to memory, processor and peripherals.
Memory assignment is dedicated, but processor usage is generally assign as a percentage of processor time, and allowed to float to an
available processor as required.
The next page illustrates the concept in a different way.