Introduction - Introduction to Computer Science - Lecture Slides, Slides of Computer Science

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Introduction

Introduction

• What Operating Systems Do
• Computer-System Organization
• Computer-System Architecture
• Operating-System Structure
• Operating-System Operations
• Process Management
• Memory Management
• Storage Management
• Protection and Security
• Distributed Systems
• Special-Purpose Systems
• Computing Environments
• Open-Source Operating Systems

What is an Operating System?

• A program that acts as an intermediary

between a user of a computer and the

computer hardware

• Operating system goals:

– Execute user programs and make solving user

problems easier

– Make the computer system convenient to use

– Use the computer hardware in an efficient

manner

Computer System Structure

• Computer system can be divided into four

components

• Hardware – provides basic computing resources
  • CPU, memory, I/O devices
• Operating system
  • Controls and coordinates use of hardware among various applications and users
• Application programs – define the ways in which the system resources are used to solve the computing problems of the users - Word processors, compilers, web browsers, database systems, video games
• Users
  • People, machines, other computers

Operating System Definition

• OS is a resource allocator

– Manages all resources

– Decides between conflicting requests for

efficient and fair resource use

• OS is a control program

– Controls execution of programs to prevent

errors and improper use of the computer

Operating System Definition (Cont)

• No universally accepted definition
• “Everything a vendor ships when you order an

operating system” is good approximation

• But varies wildly
• “The one program running at all times on the

computer” is the kernel. Everything else is either a system program (ships with the operating system) or an application program

Computer System Organization

• Computer-system operation

– One or more CPUs, device controllers connect

through common bus providing access to shared

memory

– Concurrent execution of CPUs and devices

competing for memory cycles

Computer-System Operation

• I/O devices and the CPU can execute concurrently

• Each device controller is in charge of a particular

device type

• Each device controller has a local buffer

• CPU moves data from/to main memory to/from

local buffers

• I/O is from the device to local buffer of controller

• Device controller informs CPU that it has finished

its operation by causing an interrupt

Interrupt Handling

• The operating system preserves the state of the

CPU by storing registers and the program counter

• Determines which type of interrupt has occurred:

• polling
• vectored interrupt system

• Separate segments of code determine what

action should be taken for each type of interrupt

Interrupt Timeline

Direct Memory Access Structure

• Used for high-speed I/O devices able to

transmit information at close to memory

speeds

• Device controller transfers blocks of data from

buffer storage directly to main memory

without CPU intervention

• Only one interrupt is generated per block,

rather than the one interrupt per byte

Storage Structure

• Main memory – only large storage media that the

CPU can access directly

• Secondary storage – extension of main memory

that provides large nonvolatile storage capacity

• Magnetic disks – rigid metal or glass platters

covered with magnetic recording material

• Disk surface is logically divided into tracks , which are subdivided into sectors
• The disk controller determines the logical interaction between the device and the computer

Storage-Device Hierarchy

Caching

• Important principle, performed at many levels in a

computer (in hardware, operating system, software)

• Information in use copied from slower to faster

storage temporarily

• Faster storage (cache) checked first to determine if

information is there

• If it is, information used directly from the cache (fast)
• If not, data copied to cache and used there
• Cache smaller than storage being cached
• Cache management important design problem
• Cache size and replacement policy