Operating System Support - Processor Architecture and Microprogramming - Lecture Slides, Slides of Computer Architecture and Organization

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Chapter 8

Operating System Support

Objectives and Functions

• Convenience —Making the computer easier to use
• Efficiency —Allowing better use of computer resources

Operating System Services

• Program creation
• Program execution
• Access to I/O devices
• Controlled access to files
• System access
• Error detection and response
• Accounting

O/S as a Resource Manager

Early Systems

• Late 1940s to mid 1950s
• No Operating System
• Programs interact directly with hardware
• Two main problems: —Scheduling —Setup time

Simple Batch Systems

• Resident Monitor program
• Users submit jobs to operator
• Operator batches jobs
• Monitor controls sequence of events to process batch
• When one job is finished, control returns to Monitor which reads next job
• Monitor handles scheduling

Job Control Language

• Instructions to Monitor
• Usually denoted by $
• e.g. —$JOB —$FTN —... Some Fortran instructions —$LOAD —$RUN —... Some data —$END

Desirable Hardware Features

• Memory protection —To protect the Monitor
• Timer —To prevent a job monopolizing the system
• Privileged instructions —Only executed by Monitor —e.g. I/O
• Interrupts —Allows for relinquishing and regaining control

Single Program

Multi-Programming with Two Programs

Utilization

Time Sharing Systems

• Allow users to interact directly with the computer —i.e. Interactive
• Multi-programming allows a number of users to interact with the computer

Long Term Scheduling

• Determines which programs are submitted for processing
• i.e. controls the degree of multi-programming
• Once submitted, a job becomes a process for the short term scheduler
• (or it becomes a swapped out job for the medium term scheduler)

Medium Term Scheduling

• Part of the swapping function (later…)
• Usually based on the need to manage multi- programming
• If no virtual memory, memory management is also an issue