Apple - Introducing OS X Lion

Apple - Introducing OS X Lion

Get a closer look at OS X Lion, the world's most advanced desktop operating system. With features like Mission Control, Launchpad, full-screen apps, and new gestures, OS X Lion takes Mac further than ever.

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Apple - Introducing OS X Lion

Operating System Support - Scheduling

Scheduling

• Key to multi-programming
• Long term
• Medium term
• Short term
• I/O

 

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

Operating System Support - Scheduling

Operating System Support - Part 2

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

Multi-programmed Batch Systems

• I/O devices very slow
• When one program is waiting for I/O, another can use the CPU

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

Operating System Support - Part 2

Operating System Support

• 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

Types of Operating System

• Interactive 
• Batch 
• Single program (Uni-programming) 
• Multi-programming (Multi-tasking)

Early Systems

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

Operating System Support