Chapter 1: Introduction
Operating System Concepts – 9th Edit9on Silberschatz, Galvin and Gagne ©2013
Chapter 1: 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
Kernel Data Structures
Computing Environments
Open-Source Operating Systems
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Objectives
To describe the basic organization of computer systems
To provide a grand tour of the major components of
operating systems
To give an overview of the many types of computing
environments
To explore several open-source operating systems
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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: user tasks
Execute user programs and make solving user problems
easier
in the middle between user
and Make the computer system convenient to use easy to use
hardware
Use the computer hardware in an efficient manner
and correct manner
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Computer System Structure
Computer system can be divided into four components: IUSV[ZKX33#33NGXJ]GXK33YULZ]GXK
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
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Four Components of a Computer System
works in series
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What Operating Systems Do
resource utilization = percentage
Depends on the point of view (Desktop / Laptop) of busy time
Users want convenience, ease of use and good performance
Don’t care about resource utilization resource = any hardware components response time
But shared computer such as mainframe or minicomputer must
many users
keep all users happy
many users on different devices (ex : data base)
Users of dedicate systems such as workstations have dedicated
resources but frequently use shared resources from servers
tablets and mobiles
Handheld computers are resource poor, optimized for usability
and battery life
Some computers have little or no user interface, such as
embedded computers in devices and automobiles
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Operating System Definition
hardware
OS is a resource allocator users cannot allocate resources by them self
Manages all resources
Decides between conflicting requests for efficient and
fair resource use
OS is a control program software
Controls execution of programs to prevent errors and
improper use of the computer
middle layer between user and hardware
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Operating System Definition (Cont.)
os = shell + kernal (core for os)
No universally accepted definition
“Everything a vendor ships when you order an operating
system” is a 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.
software = 1-user programms
2-kernal
3-shell
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Computer Startup
uploads os
bootstrap program is loaded at power-up or reboot
Typically stored in ROM or EPROM, generally known
as firmware
Initializes all aspects of system
Loads operating system kernel and starts execution
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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
Bus
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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 if bus is not available
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 signal generated by any i/o device and goes to cpu to perform
task
cpu is busy by some task , when i/o needs service , cpu should be interrupt
interrupt happens : 1- start i/o action
2- end i/o action
user clicks on keyboard , what should happen ?
1-stop current task , ex : A exe (saving info that help to return to stop point)
2-manage how user click should be handled
3-returns to A exe from where he stopped
cpu operations in interrupt driven
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interrupt is hardware generated signal
Common Functions of Interrupts
Interrupt transfers control to the interrupt service routine
generally, through the interrupt vector, which contains the interrupt vector is like a
table contains interrupt
addresses of all the service routines name and its pointer to
Interrupt architecture must save the address of the what to do
interrupted instruction
A trap or exception is a software-generated interrupt
caused either by an error or a user request
trap : software generated signal going to cpu
An operating system is interrupt driven
exception : error interrupt
interrupt cpu is interrupt
interrupt os in trap
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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 no interrupt
vectored interrupt system
Separate segments of code determine what action should
be taken for each type of interrupt
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Interrupt Timeline
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I/O Structure
After I/O starts, control returns to user program only upon I/O
completion
pause
Wait instruction idles the CPU until the next interrupt
Wait loop (contention for memory access) polling (cpu watching i/o )
At most one I/O request is outstanding at a time, no
simultaneous I/O processing
After I/O starts, control returns to user program without waiting
for I/O completion
System call – request to the OS to allow user to wait for
interrupt types I/O completion
Device-status table contains entry for each I/O device
indicating its type, address, and state
OS indexes into I/O device table to determine device
status and to modify table entry to include interrupt
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Storage Hierarchy
Storage systems organized in hierarchy
Speed
Cost
Volatility
Caching – copying information into faster storage system;
main memory can be viewed as a cache for secondary
storage
Device Driver for each device controller to manage I/O
Provides uniform interface between controller and
kernel
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Storage-Device Hierarchy
fast & small
slow &
large
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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
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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
DMA : improve performance for cpu without many disruption (interrupt)
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How a Modern Computer Works
A von Neumann architecture
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Computer-System Architecture
Most systems use a single general-purpose processor
Most systems have special-purpose processors as well
Multiprocessors systems growing in use and importance
Also known as parallel systems, tightly-coupled systems
Advantages include:
1. Increased throughput
2. Economy of scale
3. Increased reliability – graceful degradation or fault tolerance
Two types:
1. Asymmetric Multiprocessing – each processor is assigned a
specie task.
2. Symmetric Multiprocessing – each processor performs all tasks
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Symmetric Multiprocessing Architecture
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A Dual-Core Design
multichip for multicores 1 chip with multicors
Multi-chip and multicore
Systems containing all chips
Chassis containing multiple separate systems
multicore
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Operating System Structure
multiple processes to end
Multiprogramming (Batch system) 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 who will come after the last one
When it has to wait (for I/O for example), OS switches to another job
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 processes remain until the os determined
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
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Memory Layout for Multiprogrammed System
user applications processes
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Operating-System Operations
Interrupt driven (hardware and software)
Hardware interrupt by one of the devices
Software interrupt (exception or trap):
Software error (e.g., division by zero) exception
Request for operating system service trap
Other process problems include infinite loop, processes
modifying each other or the operating system
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Operating-System Operations (cont.)
Dual-mode operation allows OS to protect itself and other system
components
User mode and kernel mode
Mode bit provided by hardware its like a flag with only single bit
Provides ability to distinguish when system is running user
code or kernel code
forbidden on user mode (any instructions want hardware)
Some instructions designated as privileged, only
executable in kernel mode
System call changes mode to kernel, return from call resets
it to user
Increasingly CPUs support multi-mode operations
i.e. virtual machine manager (VMM) mode for guest VMs
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Transition from User to Kernel Mode
Timer to prevent infinite loop / process hogging resources
Timer is set to interrupt the computer after some time period
Keep a counter that is decremented by the physical clock.
Operating system set the counter (privileged instruction)
When counter zero generate an interrupt go back from kernel mode to user mode
Set up before scheduling process to regain control or terminate
program that exceeds allotted time
gray -> blue (hardware call)
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Kernel Data Structures
n Many similar to standard programming data structures
n Singly linked list
n Doubly linked list
n Circular linked list
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Kernel Data Structures
Binary search tree
left <= right
Search performance is O(n)
Balanced binary search tree is O(lg n)
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Kernel Data Structures
Hash function can create a hash map
Bitmap – string of n binary digits representing the status of n items
Linux data structures defined in
include files <linux/list.h>, <linux/kfifo.h>,
<linux/rbtree.h>
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Computing Environments - Virtualization
Use cases involve laptops and desktops running multiple OSes
for exploration or compatibility
Apple laptop running Mac OS X host, Windows as a guest
Developing apps for multiple OSes without having multiple
systems
QA testing applications without having multiple systems
Executing and managing compute environments within data
centers
VMM can run natively, in which case they are also the host
There is no general purpose host then (VMware ESX and
Citrix XenServer)
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Computing Environments - Virtualization
interface
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Read Only
Open-Source Operating Systems
Operating systems made available in source-code format rather
than just binary closed-source
Counter to the copy protection and Digital Rights
Management (DRM) movement
Started by Free Software Foundation (FSF), which has
“copyleft” GNU Public License (GPL)
Examples include GNU/Linux and BSD UNIX (including core of
Mac OS X), and many more
Can use VMM like VMware Player (Free on Windows), Virtualbox
(open source and free on many platforms -
http://www.virtualbox.com)
Use to run guest operating systems for exploration
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End of Chapter 1
Operating System Concepts – 9th Edit9on Silberschatz, Galvin and Gagne ©2013
