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 : 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 –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 ↓ OS initiates a user program ↓ Execute the user program ↓ Clean the job ↓ OS initiate another user program