Transcript Chap 1 Introduction

Chap 1 Introduction
• What is OS?
• OS is a program that interfaces users and
computer hardware.
• Purpose: Provides an environment for
users to execute programs.
• Goal: convenient to use a computer
system and in an efficient manner to use
computer hardware
1.1 Features provided by OS
– defining user interface
– sharing the computer hardware among
users
– allowing users to share data – common data
– scheduling resources among users
– facilitating input/output
– recovering from error
1.2 The key resources an OS manages :
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processors ( cpu or other processors )
storage ( primary and secondary )
I/O devices
Data ( files )
Internal devices : clock, timers
Processes
2. Generations of OS
• 2.1 Hardware generations
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1st generation : vacuum tubes
2nd generation : transistors
3rd generation : integrated circuits (IC)
4th generation: LSI and VLSI
• Future direction:
– reduce the cost
– reduce the energy consumption
– increase operating speed
– increase capacity
2.2 Zero generation of OS (1940s)
• Features
• Hardware only, without OS
• Users had completely access to machine
language.
• Users had to hand-code all instructions.
• Load in the program manually on the front
panel.
2.3 1st generation of OS (1950s) – Batch
processing system
• For smoothing the transition between jobs
• The flow chart of running an application program
• Power on the computer
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• OS initiates a user program
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• Execute the user program
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• Clean the job
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• OS initiate another user program