01-Introduction

1 .Operating systems 1 1. Introduction 1.1 The Role of Operating Systems Bridge the “Semantic Gap” between Hardware and Application Three Views of Operating System 1. Abstraction (addresses complexity) 2. Virtualization (addresses sharing) 3. Resource management (addresses performance) Fall, 2010

2 .Operating systems 2 Single CPU System Fall, 2010 Without OS: There is no program in memory (RAM) – how can we load it? There are no files on secondary storage (disk) – how to save anything? The screen is blank – no program is running, no prompt We cannot type or use the mouse – no one is listening Without OS the system is dead Need OS to start system and to use any hardware component OS bridges part of the Semantic Gap

3 .Operating systems 3 What is the Semantic Gap Hardware capabilities are very low level Arithmetic and logical operators Comparison of two bit-strings Branching, reading, and writing bytes User needs to think in terms of problem to be solved High-level data structures and corresponding operations Simple, uniform interfaces to subsystems Treat programs and data files as single entities Use software to bridge this gap Language processors (e.g., assemblers, compilers, interpreters ) Editors and text processors, linkers and loaders Application programs, utility and service programs Operating Systems Fall, 2010

4 .Operating systems 4 PC Hardware Organization Fall, 2010 C onsider the complexity of a real system: OS must somehow manage all this complexity for the user

5 .Operating systems 5 The role of OSs Bridge Hardware/Application Gap Machine instruction vs high level operation compiler bridges gap Linear memory vs data structures compiler bridges gap Single CPU & l imited memory vs more needed OS bridges gap Secondary memory devices vs files OS bridges gap I/O devices vs high level I/O commands OS bridges gap Fall, 2010

6 .Operating systems 6 Three views of OSs OS is an extended machine Principle of abstraction hides complexity OS provides high level operations using lower level operations OS is a virtual machine Principle of virtualization supports sharing OS provides virtual CPU, memory, devices OS is a resource manager Balance overall performance with individual needs (response time, deadlines) Fall, 2010

7 .Some observations In this course we study principles of OS no specific system Why? Systems change, principle are permanent E.g.: virtual memory, file organization, … Course is problem-oriented : Concrete problems with precise solutions No memorization, only how-to knowledge and why Operating systems Fall, 2010 7