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Operating Systems
Chapter 1
Outline
• How does this class operate?
• History & Examples of Operating Systems
• High level introduction to Operating
Systems
– What is an Operating System?
• Why study Operating Systems?
• Conclusion
Course Administration
• Text Book: Operating Systems Concepts, 7th Edition Silbershatz,
Galvin, Gagne
• References: Wikibook, Wikipedia, OER (open courseware)
• TAs.
• Office hours:
• Web Page: www.ksu-it.com/cap332
• Terms and Policies
• Mailing list
• Rough Grading Breakdown
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Exams: Three exams 10%~15% each
Exam dates (3/11/07, 1/12/07, 5/1/08)
Assignments 10%~15%, you need to work with Linux
Class Participation 5%, using a Wiki
Course prerequisites
Data Structures
Assembly
Programming
Computer Architecture
SW-Engineer (Preferable)
Course Objectives
• Short term goals
– Gain a good knowledge of OS in general, and
how their internals work
• Long term goals
– This course is the basis for future work in
other areas of OS:
• hacking Linux, i.e. contribute to the Open source
OS :-)
• postgraduate degree with an OS major
Topic Coverage
• Fundamentals (Operating Systems
Structures)
• Process Control and Threads
• Synchronization and scheduling
• VM, Protection, Address translation,
Caching
• File Systems, I/O
• ~Security, Networking
Let us begin!
Computing Devices Everywhere
Computing Devices Everywhere
• Operating Systems drive the inner
workings of virtually every computer in the
world today
• PCs, servers, iPods, cell phones, missile
guidance systems, etc. all have an OS that
dictate how they operate.
• The OS manages many aspects of how
programs run, and how they interact with
hardware and the outside world.
Understanding the OS is essential
for understanding:
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System performance and reliability
Resource management
Virtualization and abstraction
Concurrency and parallelism
Hardware interfaces and I/O
IS OS Development easy?
• Developing huge OS needs a lot of Man-Power,
Organization and Budget, e.g.
– Windows Vista has approx. 30 Million lines of code
– I recommend visiting Channel 9
(http://channel9.msdn.com/), Example video:
Windows Vista PreOS Environment: What
happens before the OS loads
– *nix OS has an interesting story, search for Richard
Stallman and Linus Torvalds in Google Video.
– I highly recommend watching “Triumph of the Nerds.”
Organization & Components
of a computer system
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
Three Components of a
Computer System
• A computer system consists of
– hardware
– system programs
– application programs
Four Components of a Computer
System
What does an Operating System
do?
• Silberschatz and Gavin:
“An OS is Similar to a government”
• Coordinator and Traffic Cop:
– Manages all resources
– Settles conflicting requests for resources
– Prevent errors and improper use of the computer
• Facilitator:
– Provides facilities that everyone needs
– Standard Libraries, Windowing systems
– Make application programming easier, faster, less error-prone
• Some features reflect both tasks:
– E.g. File system is needed by everyone (Facilitator)
– But File system must be Protected (Traffic Cop)
What is an Operating System,…
Really?
• Most Likely:
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Memory Management
I/O Management
CPU Scheduling
Communications? (Does Email belong in OS?)
Multitasking/multiprogramming?
• What about?
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File System?
Multimedia Support?
User Interface?
Internet Browser?
What is an OS?
User Application
User Application
User Application
Protection
Boundary
Kernel
Memory Management
File System
Device Drivers
CPU Scheduling
Disk I/O
Process Mang.
Multitasking
Networking
Hardware/
Software
interface
Hardware
Operating System Definition
• 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
What if we didn’t have an OS?
• Source
CodeCompilerObject
CodeHardware
• How do you get object
code onto the hardware?
• How do you print out the
answer?
• Once upon a time, had to
Toggle in program in
binary and read out
answer from LED’s!
Altair 8080
What if we didn’t have an OS?
Early batch system
– bring cards to 1401
– read cards to tape
– put tape on 7094 which does computing
– put tape on 1401 which prints output
Operating System Structure
Operating System Structure
• Multiprogramming needed for efficiency
– Single user cannot keep CPU and I/O devices
busy at all times
– Multiprogramming organizes jobs (code and
data) so CPU always has one to execute
– 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 job
Memory Layout for
Multiprogrammed System
Operating System Structure
• Timesharing (multitasking) is logical extension 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
Operating-System Operations
Operating-System Operations
• Interrupt driven by hardware
• Software error or request creates exception or
trap
– Division by zero, request for operating system service
• Other process problems include infinite loop,
processes modifying each other or the operating
system
Dual Mode Operation
• Hardware provides at least two modes:
– “Kernel” mode (or “supervisor” or “protected”)
– “User” mode: Normal programs executed
• Some instructions/ops prohibited in user mode:
– Example: cannot modify page tables in user mode
• Attempt to modify  Exception generated
• Transitions from user mode to kernel mode:
– System Calls, Interrupts, Other exceptions
Process Management (1)
• A process is a program in execution. It is a
unit of work within the system. Program is
a passive entity, process is an active
entity.
• Process needs resources to accomplish its
task
– CPU, memory, I/O, files
– Initialization data
• Process termination requires reclaim of
any reusable resources
Process Management (2)
• Single-threaded process has one program
counter specifying location of next instruction to
execute
– Process executes instructions sequentially, one at a
time, until completion
• Multi-threaded process has one program
counter per thread
• Typically system has many processes, some
user, some operating system running
concurrently on one or more CPUs
– Concurrency by multiplexing the CPUs among the
processes / threads
Process Management Activities
The operating system is responsible for the following
activities in connection with process management:
• Creating and deleting both user and system processes
• Suspending and resuming processes
• Providing mechanisms for process synchronization
• Providing mechanisms for process communication
• Providing mechanisms for deadlock handling
Memory Management (1)
• All data in memory before and after
processing
• All instructions in memory in order to
execute
• Memory management determines what is
in memory when
– Optimizing CPU utilization and computer
response to users
Memory Management (2)
• Memory management activities
– Keeping track of which parts of memory are
currently being used and by whom
– Deciding which processes (or parts thereof)
and data to move into and out of memory
– Allocating and deallocating memory space as
needed
Storage Management (1)
• OS provides uniform, logical view of
information storage
– Abstracts physical properties to logical storage
unit - file
– Each medium is controlled by device (i.e., disk
drive, tape drive)
• Varying properties include access speed, capacity,
data-transfer rate, access method (sequential or
random)
Storage Management (2)
• File-System management
– Files usually organized into directories
– Access control on most systems to determine
who can access what
– OS activities include
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Creating and deleting files and directories
Primitives to manipulate files and dirs
Mapping files onto secondary storage
Backup files onto stable (non-volatile) storage
media
Mass-Storage Management (1)
• Usually disks used to store data that does not fit
in main memory or data that must be kept for a
“long” period of time.
• Proper management is of central importance
• Entire speed of computer operation hinges on
disk subsystem and its algorithms
Mass-Storage Management (2)
• OS activities
– Free-space management
– Storage allocation
– Disk scheduling
• Some storage need not be fast
– Tertiary storage includes optical storage, magnetic
tape
– Still must be managed
– Varies between WORM (write-once, read-manytimes) and RW (read-write)
I/O Subsystem
• One purpose of OS is to hide peculiarities
of hardware devices from the user
• I/O subsystem responsible for
– Memory management of I/O including
buffering (storing data temporarily while it is
being transferred), caching (storing parts of
data in faster storage for performance),
spooling (the overlapping of output of one job
with input of other jobs)
– General device-driver interface
– Drivers for specific hardware devices
Protection and Security (1)
• Protection – any mechanism for controlling
access of processes or users to resources
defined by the OS
• Security – defense of the system against
internal and external attacks
– Huge range, including denial-of-service, worms,
viruses, identity theft, theft of service
Protection and Security (2)
• Systems generally first distinguish among users,
to determine who can do what
– User identities (user IDs, security IDs) include name
and associated number, one per user
– User ID then associated with all files, processes of
that user to determine access control
– Group identifier (group ID) allows set of users to be
defined and controls managed, then also associated
with each process, file
– Privilege escalation allows user to change to
effective ID with more rights
Computing Environments
• Traditional computer
– Blurring over time
– 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, networked
Computing Environments
(Cont.)
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Client-Server Computing
 Dumb terminals supplanted by smart PCs
 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
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
– Node must join P2P network
• Registers its service with central lookup service on network,
or
• Broadcast request for service and respond to requests for
service via discovery protocol
– Examples include Napster and Gnutella
Web-Based Computing
• Web has become ubiquitous
• PCs most prevalent devices
• More devices becoming networked to allow web
access
• New category of devices to manage web traffic
among similar servers: load balancers
• Use of operating systems like Windows 95,
client-side, have evolved into Linux and
Windows XP, which can be clients and servers
Chapter Conclusion
OS Systems Principles
• OS as illusionist:
– Make hardware limitations go away
– Provide illusion of dedicated machine with infinite memory and
infinite processors
• OS as government:
– Protect users from each other
– Allocate resources efficiently and fairly
• OS as complex system:
– Constant tension between simplicity and functionality or
performance
• OS as history teacher
– Learn from past
– Adapt as hardware tradeoffs change
Why Study OS?
• Learn how computer works
• Learn how to build complex systems:
– How can you manage complexity for future projects?
• Engineering issues:
– Why is the web so slow sometimes? Can you fix it?
– How do large distributed systems work? (Kazaa, etc)
• Buying and using a personal computer:
– Why different PCs with same CPU behave differently
– How to choose a processor (Itanium, Celeron, Pentium, etc)?
– Should you get Windows XP, 2000, Linux, Mac OS …?
• Because OS is everywhere!!
Conclusion
• Operating systems provide a virtual machine
abstraction to handle diverse hardware
• Operating systems coordinate resources and
protect users from each other
• Operating systems simplify application
development by providing standard services
• Operating systems can provide an array of fault
containment, fault tolerance, and fault recovery
References
• Pictures & some slides
– Prof. Kubiatowicz & Prof. Anthony, Berkeley
university, Prof. Welsh, Harvard University
– Modern OS slides by A. Tanenbaum
• Content
– Text book
– Modern OS Book
– Wikipedia
• http://en.wikipedia.org/wiki/History_of_the_Linux_kernel
• http://en.wikipedia.org/wiki/Operating_system
• And much more