ENVS 1800 Chapter Notes - Chapter 17: Minos, Program Counter, Microcomputer
14 May 2018
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ENVS 1800 Chapter 17 Notes – Summary
Introduction
• The two major components of the kernel were the process scheduler/memory manager
and the dispatcher.
• MINOS was capable of manipulating up to five user programs at a time.
• The process scheduler handled requests for program loading.
• The header for a program to be loaded specified a priority level and a memory size
requirement.
• Programs were loaded into the smallest available memory space of the correct priority
level that would fit the program.
• Of course, there was only a single memory area available for each program of the
highest and lowest priorities.
• If space was not available, the process scheduler notified the user
• It was up to the user to determine which program, if any, should be unloaded to make
room.
• For each program in memory, there was an entry in a process control table
• Recall that at any instant in time, one process per CPU is running, while the others are
ready to run or waiting for an event, such as I/O completion, to occur.
• The process control table shows the status of each program and the program counter
locations where the program will restart when it is next run.
• In MINOS, it also contained locations for storage and restoration of each of the two
registers that were present in the microcomputer that was used.
• There was also one additional register that kept track of which mid-priority process,
partition 2, partition 3, or partition 4, was run most recently.
• We called this register the mid-priority process run last, or MPRL, register.
• Since there was one entry in the process table for each partition, the priority value for
each program was already known by the operating system.
• The most interesting part of MINOS was the program dispatcher.
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