FIT2100 Study Guide - Final Guide: Context Switch, Paging, Design Issues
30 May 2018
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FIT2100 - Exam Notes
Lecture 1&2 - Computer System and Operating Systems
What is an Operating System
OS: a low-level software that supports a computer’s basic functions, manages computer hardware
and software
-A program that controls the execution of application programs
-An interface between applications and hardware
-Main objective
-Convenience
-Efficiency
-Ability to evolve
-exploits the hardware resources of one or more processors
-Provides a set of services to system users
-Manages secondary memory and I/O devices on behalf of its users
-The operating system takes care of scheduling of tasks on individual processors and of
synchronisation among processors
Operating System Services:
-Program development
-Program execution
-Access I/O devices
-Controls access to files
-System access
-Error detection and response
-Accounting
Role of Operating System
-A computer is a set of resources for the movement, storage and processing of data
-OS is responsible for managing these resources
-OS is in control of the computer’s basic functions
OS: As software
-OS functions in the same way as ordinary computer software
-Program, or suite of programs, executed by the processor
-Frequently relinquishes control and must depend on the processor to allow it to regain control
-OS provides instructions to the processor and directs the processor in terms of the use of other
system resources and the timing of execution for other programs
OS: As Resource Manager
-manages and allocates resources to programs
OS: As Control Program
-controls the execution of user programs and operation of I/O devices
OS: as Kernel
-the one program running at all times (all else being application programs)
Concept of Process
Process can be defined as:
-A program in execution
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-An instance of a running program
-The entity that can be assigned to, and executed on, a processor
-A unit of activity characterised by a single sequential thread of execution, a current state, and
an associated set of system resources
Three components:
-An executable program
-Associated data needed by the program
-Execution context of the program
-This component is essential as it is the internal data by which the Os is able to supervise and
control the process
-Includes the contents of the various process registers
-Includes information such as the priority of the process; and whether the process is waiting
for the completion of a particular I/O event
Process Management
-the process is realised as a data structure
-The entire state of the process at any instant is contained in its context
-New features can be designed and incorporated into the OS
Memory Management
-OS has five principal storage management responsibilities
-Process isolation
-Automatic allocation and management
-Support of modular programming
-Protection and access control
-Long-term storage
-Can be achieved using virtual memory and file system facilities
Information Protection and Security
-The nature of the the threat that concerns an organisation will vary greatly depending on the
circumstances
-Concern involves controlling access to computer systems and the information stored in the
systems
-Main issue
-Availability
-Confidentiality
-Date integrity
-Authenticity
Scheduling and Resource Management
-Key responsibilities of an Os: managing various system resources (main memory, I/O devices,
processors)
-Resource allocation and scheduling policies must consider
-Fairness: equal and fair access to resources by competing processes
-Differential responsiveness: discriminate among different classes of processes
-Efficiency: maximise throughput and minimise response time; accomodate as many users as
possible
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OS Architecture for UNIX/LINUX, Android and Windows
-Demands on operating systems require new approaches to organising the OS architecture
Linux Systems:
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-started out as UNIX variant for the IBM PC
-Initial version was written by Linus Torvalds, a Finnish student
-First posted on the internet in 1991
-Today it is a full-featured UNIX system that runs on several platforms
-Free and source code available
-Key to success has been the availability of free software packages
-Highly modular and easily configured
Android OS:
-a Linux-based system originally designed for touchscreen mobile devices such as smartphones
and tablet computers
-The Open Handset Alliance (OHA) was responsible for the Android os release as an open
platform
-The open-source nature of Android has been the key to its success
Basic Elements of a Computer System
Processor:
-Controls the operation of the computer
-Performs the data processing functions
-Central Processing Unit (CPU)
I/O Modules:
-Moves data between the computer and external environments
—> storage (e.g. hard disk)
—> communications equipments
—> terminals
Main Memory:
-Stores data and programs
-Volatile —> contents of the memory is lost when the computer is shut down
-a.k.a real memory or primary memory or random access memory
System Bus:
-Provides for communication among processors, main memory, and I/O modules
-Comprises of:
-Address bus
-Data bus
-Control bus
Top Level View
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Document Summary
Lecture 1&2 - computer system and operating systems. Os: a low-level software that supports a computer"s basic functions, manages computer hardware and software. A program that controls the execution of application programs. Exploits the hardware resources of one or more processors. Provides a set of services to system users. Manages secondary memory and i/o devices on behalf of its users. The operating system takes care of scheduling of tasks on individual processors and of synchronisation among processors. A computer is a set of resources for the movement, storage and processing of data. Os is responsible for managing these resources. Os is in control of the computer"s basic functions. Os functions in the same way as ordinary computer software. Program, or suite of programs, executed by the processor. Frequently relinquishes control and must depend on the processor to allow it to regain control.
