CS212: OPERATING SYSTEM
Lecture 1: Introduction
1
2
Chapter 1: Introduction What Operating Systems Do Computer-System Organization Computer-System Architecture Operating-System Structure Operating-System Operations Distributed Systems Computing Environments
3
Objectives To provide a grand tour of the major operating systems
components To provide coverage of basic computer system organization
4
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
5
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
6
Four Components of a Computer System
7
The operating system’s Role User View:
Single User (personal computer) OS designed for ease of use , with some attention paid to
performance. Multiple User’s (mainframe or minicomputer)
OS designed to maximize resource utilization. Workstations users connected to networks of other
workstations and servers OS designed to compromise between individual usability and
resource utilization.
8
The operating system’s Role (cont.)
System View: OS is a resource allocator
Manages all resources Decides between conflicting requests for efficient and
fair resource use It is important when many users access the same
mainframe or minicomputer OS is a control program
Controls execution of programs to prevent errors and improper use of the computer
It is especially concerned with the operation and control of I/O devices.
9
Operating System Definition
No universally accepted definition “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.
An operating system is a software that manages the computer hardware, as well as providing an
environment for application programs to run.
10
Computer-System Organization Computer-System Operation Storage Structure I/O Structure
11
Computer System operation 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
12
Computer System Operation (cont.)Computer Startup: bootstrap program is loaded at power-up or reboot
Typically stored in ROM or EEPROM, generally known as firmware
Initializes all aspects of system Loads operating system kernel and starts execution
13
Computer System Operation (cont.)Interrupt: The occurrence of an event is usually signaled by an
interrupt from either the hardware or the software. Hardware interrupts by sending a signal to the CPU through
system bus. Software interrupts by executing a special operation called a
system call.The interrupt is signal that gets the attention of the CPU and is usually generated when I/O is required. For example, hardware interrupts are generated when a key is pressed or when the mouse is moved. Software interrupts are generated by a program requiring disk input or output.
14
Storage Hierarchy Storage systems organized in hierarchy
Speed Cost Volatility
Caching – copying information into faster storage system; main memory can be viewed as a last cache for secondary storage
15
Storage-Device Hierarchy
16
I/O Structure each device controller is in charge of a specific type of
device. A device controller maintains some local buffer storage
and a set of special-purpose registers. OS have a device driver for each device controller.
This device driver understands the device controller and presents a uniform interface to device to the rest of the operating system.
17
Computer-System Architecture Multiprocessors systems growing in use and importance
Also known as parallel systems, tightly-coupled systems Advantages include
1. Increased throughput2. Economy of scale3. Increased reliability – fault tolerance
Two types1. Asymmetric Multiprocessing (master-slave relationship)2. Symmetric Multiprocessing (all processors are peers)
18
Symmetric Multiprocessing Architecture
19
A Dual-Core Design• Processors were originally developed with only one core. • The core is the part of the processor that actually performs the reading and executing of the instruction. Single-core processors can only process one instruction at a time• Dual-core processor contains two cores (Such as Intel Core Duo).
20
Operating System Structure
Multiprogramming needed for efficiency Multiprogramming organizes jobs (code and data) so CPU
always has one to execute. (Increase CPU Utilization.) A subset of total jobs in system is kept in memory One job selected and run via job scheduling When it has to wait (for I/O for example), OS switches to
another jobMultiprogramming systems provide an environment inwhich the various system resources are utilized effectively,Not for user interaction with the computer system
21
Memory Layout for Multiprogrammed System
Uniprogramming Processor must wait for I/O
instruction to complete before preceding
22
Multiprogramming When one job needs to wait for
I/O, the processor can switch to the other job
23
24
Multiprogramming
25
Utilization Histograms
26
Example
27
Operating System Structure (cont.)
Timesharing (multitasking) is logical extension of multiprogramming in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing Response time should be < 1 second Each user has at least one program executing in memory
process If several jobs ready to run at the same time CPU
scheduling If processes don’t fit in memory, swapping moves them
in and out to run Virtual memory allows execution of processes not
completely in memory
28
Time Sharing Using multiprogramming to handle
multiple interactive jobs Processor’s time is shared among
multiple users Multiple users simultaneously access the
system through terminals
29
Operating-System Operations Dual-mode operation allows OS to protect itself and other
system components User mode and kernel mode Mode bit provided by hardware
Provides ability to distinguish when system is running user code or kernel code
Some instructions designated as privileged, only executable in kernel mode
System call changes mode to kernel, return from call resets it to user
30
Transition from User to Kernel Mode
31
Distributed Systems Distributed systems allow users to share resources on
geographically dispersed hosts connected via a computer network.
The basic types of networks are: Local-area Network (LAN) connects computers within a room, a
floor, or a building. Wide-area Network (WAN) links building, cities or countries.
A network operating system provides features such as file sharing across the network and includes a communication scheme that allows different
processes on different computers to exchange messages
32
Computing Environments Traditional computing (Centralized computing)
Office environment PCs connected to a network, terminals attached to
mainframe or minicomputers providing batch and timesharing
Now portals allowing networked and remote systems access to same resources
Home networks Used to be single system, then modems Now firewalled, networkedCentralized computing is computing done at a central
location, using terminals that are attached to a central computer.
33
Computing Environments (Cont)
Client-Server Computing Many systems now servers, responding to requests generated
by clients Compute-server provides an interface to client to request
services (i.e. database) File-server provides interface for clients to store and
retrieve files
34
Peer-to-Peer Computing Another model of distributed system P2P does not distinguish clients and servers
Instead all nodes are considered peers May each act as client, server or both To participate in a P2P system, a node must join P2P network
by: Registers its service with centralized lookup service on
network, or Broadcast request for service and respond to requests for
service via discovery protocol
Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8th Edition,
End of Chapter 1