Summary OfOperating System

 

William Stallings Computer Organization and Architecture

Chapter 7 Operating System Support

Early System

Late 1940s to mid-1950s

·        No Operating System

·        Programs interact directly with hardware

·        Two main problems:

§      Scheduling

§      Setup time

Types of OS

·        Interactive

·        Batch

·        Single program (Uni-programming)

·        Multi-programming (Multi-tasking)

 

OS as a Resource Manager

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 which reads next job

·        Monitor handles 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

 

Short-term Scheduling

·        Dispatcher

·        Fine grained decisions of which job to execute next

·        i.e. which job actually gets to use the processor in the next time slot

 

Process Control Back

·        Identifier

·        State

·        Priority

·        Program counter

·        Memory pointers

·        Context data

·        I/O status

·        Accounting information

 

Process State

 

Memory Management

·        Uni-program

o   Memory split into two

o   One for Operating System (monitor)

o   One for currently executing program

·        Multi-program

o   “User” part is sub-divided and shared among active processes

 

Key Elements of OS