Operating Systems
Designed and Presented by
Dr. Ayman Elshenawy Elsefy
Dept. of Systems & Computer Eng..
AL-AZHAR University
Website : eaymanelshenawy.wordpress.com
Email : eaymanelshenawy@Azhar.edu.eg
eaymanelshenawy@yahoo.com
Operating Systems
1.1
Operating Systems
Reference
Operating System Concepts, ABRAHAM
SILBERSCHATZ
Part 1:
Overview of Operating system
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
Distributed Systems
Special-Purpose Systems
Computing Environments
Open-Source Operating Systems
Computer System Organization
Computer system consists of:
One or more CPU’s.
A set of device controllers (disk drives, audio devices,…)
connected through a common bus with a shared memory.
The CPU and device controllers can execute concurrently
competing for memory cycles.
A memory controller synchronize access to the shared memory
in ordered way.
Computer System Structure divided into four components
Users: People, machines,
other computers
Application & system programs – how system resources are used
to solve the computing problems of the users (Word processors,…)
Operating
system:
Controls
and
coordinates HW among
various
applications
and users
Hardware:
basic
computing resources (
CPU,
memory,
I/O
devices)
Computer System Structure
Hardware:
CPU, memory, and I/O devices
provides the basic computing resources for the system.
Application Programs:
Word processors, Spreadsheets, compilers, and Web browsers.
Define the ways in which these resources are used to solve users’
computing problems.
Operating System:
Support complex games, business applications, and everything in
between.
Controls the hardware and coordinates its use among the various
application programs for the various users.
Like a government, it performs no useful function by itself. It simply
provides an environment within which other programs can do useful
work.
What is an Operating System?
A program that:
mange computer Hardware.
The basis for Application programs.
Intermediate between user applications and computer H.W.
Mainframe OS:
Are designed primarily to optimize HW utilization.
Personal computer (PC) OS:
Support complex games, business applications, and everything in
between.
Mobile computers:
Provide an environment in which a user can easily interface with the
computer to execute programs.
OS are designed to be convenient, efficient, and some
combination of the two.
What is an Operating System?
OS Consists of.
Kernel
A program run at all times on the computer.
Systems
programs are associated with the OS but are not
part of the kernel (run as needed).
Application
programs, all programs not associated with the
operation of the system.)
OS goals:
Execute
user programs.
Solve
user problems in easy form.
Make
the computer system convenient to use.
Use
the computer hardware in an efficient manner.
Operating Systems Role- User View
Maximize Performance (ease of use), and resource utilization according
to the interface being used.
PC computer systems users need to:

Maximize the performance

Don’t care about resource utilization.
Mainframe and Minicomputers:

Maximize resource utilization.
Dedicated systems (workstations)
have
dedicated resources but frequently use shared
resources from servers, files , printers
(
usability & resources Utilization)
Mobile Devices:

users are used touch screens
embedded computers (No user interface):

devices and automobiles (no user interaction, and no resource sharing)
Operating Systems Role- System View
OS as a Resource allocator:
Manage computer resources (CPU time, memory space, file
storage space, I/O devices, ….) to solve problems.
OS acts as a manger for these resources.
Solve conflict requests for resources,
decide how to allocate them to specific programs and users (
efficiently and fairly).
OS as a Control Program
manages the execution of user programs
prevent errors and improper use of the computer.
Concerned with the operation and control of I/O devices.
Computer-System Operation
When the computer is powered on or rebooted it must have a
bootstrap program (initial Program) to start working.
Bootstrap Program:
A
simple program, stored in (ROM/EEPROM), known by firmware,
within the computer HW.
 Initialize
all the system, from CPU registers to device controllers to
memory contents.
 Locate
the OS Kernel and load it into the memory.
 Start
providing services to the systems and users ( System Process
or System Daemons)
 Know
how to execute the first process, such as “init” in Unix.
Waits for some event to occur
 Hardware
 Software
 Each
Interrupt: I/O device sending signals to CPU.
Interrupt: (special operation called a system call/ Monitor Call).
computer design has its own interrupt mechanism, but several
functions are common.
Computer-System Operation
What is happened when the CPU is interrupted?
It stops what it is doing and immediately.
Execute the Interrupt Service Routine (ISR), using the memory
address in Interrupt Vector Table (IVT) for each interrupt type.
After executing of ISR, the CPU resumes the computation.
Common Functions of Interrupts
Interrupt transfers control to the ISR through the interrupt
vector, which contains the addresses of all the service routines
Interrupt architecture must save the address of the interrupted
instruction
Incoming interrupts are disabled while another interrupt is being
processed to prevent a lost interrupt
A trap is a software-generated interrupt caused either by an
error or a user request
An OS is interrupt driven
Storage Structure –Main Memory
The CPU can load instructions only from memory.
Memory consists an array of words with addresses.
The CPU execute programs that located in main memory (RAM):
RAM is implemented in a semiconductor technology called dynamic
random-access memory (DRAM)..
too small to store all needed programs
Volatile : loses its contents when power is turned off or otherwise lost
Bootstrap program is typically stored in ROM or EEPROM.
ROM used to store static programs that cannot be changed (game
cartridges, manufacturers can distribute games that cannot be
modified).
EEPROM cannot be changed frequently and so contains mostly
static programs (smartphones store their factory setting).
The load instruction and store instruction moves a word from/to
main memory and the internal register within the CPU.
Computer Memory
• Computers use many different types of memory to hold data and programs.
▪ Semi-conductor Memories
▪ magnetic disks, USB sticks, DVDs etc.)
• Each type has its own characteristics and uses.
• Common types of memory:
▪
▪
▪
▪
read-only memory (ROM)
flash memory (EEPROM)
static random access memory
(SRAM)
dynamic random access memory
(DRAM).
Storage Structure –Secondary Memory
An extension of main memory.
Able to hold large quantities of data permanently.
magnetic disk,
Provides storage for both:
 Programs
 Data
(system and application).
until they are loaded into memory.
Many programs then use the disk as both the source and the
destination of their processing. Hence, the Disk management of
disk storage is very important.
Solid-state disks & Flash Memories:
Are faster than magnetic disks
Nonvolatile.
If external power is interrupted, this solid-state disk’s
controller copies the data from RAM to the magnetic disk.
Memory Hierarchy
• A computer have wide variety of storage systems (memory) can be
organized in a hierarchy (memory hierarchy) Rang from fast,
expensive internal registers, to slow, inexpensive Hard Magnetic
Disks.
• They are differ in speed, cost, size, volatility.
• Registers are:
• Matched in speed to the CPU
• Consume a significant amount of power.
• Only a small number of registers in a processor (More expensive).
• Secondary storage:
• such as hard magnetic disks.
• Small cost per stored bit is in terms of money and electrical power.
• Access time is very long when compared with registers.
• Between the registers and secondary storage
• There are a number of other forms of memory that bridge the gap
between the two.
Memory Hierarchy
• The memory hierarchy can be characterized by a number of
parameters:
• Access Type: how physically the memory read/write is done
(Random or Sequential).
• Capacity measured in bytes or KB, MB, GB or TB.
• Cycle time: the time elapsed from the start of a read operation to
the start of a next read.
• Latency: the time interval between the request for information and
the access to the first bit of that information.
• Bandwidth: the number of bits that can be accessed per second.
• Cost of a memory is usually specified as dollars/MB
• Total Cost = cost/MB * Memory Size.
Storage-Device Hierarchy
I/O Structure
Device controller:
a specific type of device.
seven or more devices can be attached to the small computer-systems
interface (SCSI- Small Computer System Interface) controller.
Have some local buffer storage & a set of special-purpose registers.
Transfer data between the I/O devices and its local buffer.
Device Driver:
Each OS has a device driver for each device controller.
 Understands the device controller
 provide Uniform interface for the device,
 loads the registers within the device controller.
Computer-System Operation- I/O Operation
To start an I/O operation: Interrupt Driven I/O
The device driver loads the appropriate registers within the
device controller.
The device controller, examines the contents of these registers
to determine what action to take (read a character from the KB).
The controller starts the transfer of data from the device to its
local buffer.
After transferring data, the device controller informs the device
driver via an interrupt that it has finished its operation.
The device driver then returns control to the OS
Interrupt Driven I/O is fine for moving small amount of data.
It can produce high overhead.
For bulk data or Disk I/O direct memory access (DMA) is
used.
Computer-System Operation- DMA
Direct Memory Access (DMA) used for bulk data movement.
After setting up buffers, pointers, and counters for the I/O device, the device
controller transfers an entire block of data directly to or from its own buffer
storage to memory, with no intervention by the CPU.
Only one interrupt is generated per block, to tell the device driver that the
operation has completed,
While the device controller is performing these operations, the CPU is
available to accomplish other work.
Computer-System Architecture
A computer system can be categorized according to the
number of general-purpose processors (CPU’s) used.
Single Processor system
Multi Processor system
Clustered system
Single Processor System
A system have
One general-purpose CPU capable of executing an instruction sets,
and user processes.
Special-purpose CPU’s that run instruction sets and does not
run user process (disk, keyboard, and graphics controllers);
 Special
purpose CPU’s May:
–
Managed by the OS, For example, PCs contain a CPU in the
keyboard to convert the keystrokes into codes to be sent to the
CPU.
–
Not Managed by the OS: a low-level components built into the
HW. The OS cannot communicate with it; they do their jobs
autonomously.
The use of special-purpose CPU is common and does not turn a
single-processor system into a multiprocessor.
If there is only one general-purpose CPU, then the system is a
single-processor system.
Multiple Processor System (Parallel systems)
A system have two or more CPU in close communication.
Sharing computer bus and sometimes clock, memory, I/O devices, mass
storage, and power supplies.
advantages:
Increased throughput. more work done in less time.
Low Cost than equivalent multiple single-processor systems.
Increased reliability. the failure of one processor will not halt the
system, only slow it down.
Increase Addressable memory and computing power.
Asymmetric multi-processor: each CPU is assigned to a specific task
in a (master –slave relationship). A master CPU controls the system;
the other CPU’s wait for the master instructions.
Symmetric multiprocessing (SMP), in which each processor performs
all tasks within the operating system.
Symmetric Multiprocessing Architecture
• N processes can run if there
are N CPUs.
• I/O must be controlled to
ensure the data reach the
appropriate CPU.
• Ensure no CPU is idle while
another
is
overloaded
(inefficiencies).
• Special hardware or software (written to allow only one master
and multiple slaves) can be used to differentiate between
symmetric and asymmetric multiprocessing.
• Uniform memory access (UMA): access to any RAM from any CPU
takes the same amount of time.
• Non-uniform memory access (NUMA): some parts of memory may
take longer to access than other parts.
A Dual-Core Design
• Include multiple computing cores on a single chip. In essence, these are
multiprocessor chips.
• They can be more efficient than multiple chips with single cores (on-chip
communication is faster than between-chip communication).
• appear to the operating system as N standard processors.
Clustered Systems
Like multiprocessor systems, but multiple systems working together
composed of two or more individual systems or nodes—joined together.
Usually sharing storage via a storage-area network (SAN)
Provides a high-availability service which survives failures
Asymmetric clustering has one machine in hot-standby mode
Symmetric clustering has multiple nodes running applications,
monitoring each other
Some clusters are for high-performance computing (HPC)
Applications must be written to use parallelization
Operating system Structure – Multi Programming
One of the most important aspects of OS.
Reasons:
A single program cannot, keep either the CPU or the I/O
devices busy at all times.
Single users frequently have multiple programs running.
Multiprogramming:
Increases CPU utilization by organizing jobs (code and
data).
The OS keeps several jobs in memory simultaneously.
If main memory is too small to accommodate all jobs,
Jobs
are kept initially on the disk in a job pool (consists of
all processes residing on disk awaiting allocation of main
memory). The set of jobs in memory can be a subset of job
pool.
OS Structure – Multi Programming
Eventually, the first job finishes waiting and gets the CPU back.
As long as at least one job needs to execute, the CPU is never
idle.
do not provide for user interaction with the computer system.
OS select one job and begins to execute it
Job may have to wait for some task, (I/O
operation),
The OS simply switches to another job. When
that job needs to wait, the CPU is switched to
another job, and so on.
In a non-multi programming system, the CPU
would sit idle.
Memory Layout for
Multiprogrammed System
OS Structure- Multi Tasking (Time Sharing)
Time sharing is a logical extension of multiprogramming.
In time-sharing systems, the CPU executes multiple jobs by
switching among them, but the switches occur so frequently
that the users can interact with each program while it is
running.
Time sharing requires an interactive computer system, which
provides direct communication between the user and the
system.
The user gives instructions to the OS using input device
(keyboard or mouse), and waits for an output device results.
Allows many users to share the computer simultaneously. The
system switches rapidly from one user to the next,
Each user is given the impression that the entire computer
system is dedicated to his use.
Time Sharing Requirements
Job Scheduling: If several jobs are ready to be brought into memory, and there
is no enough room for all of them, then the system must choose among them.
Memory Management: When the OS selects a job from the job pool, it loads
that job into memory for execution. Having several programs in memory at the
same time requires some form of memory management.
if several jobs are ready to run at the same time, the system must choose
among them. Making this decision is CPU scheduling.
Running multiple jobs concurrently requires that they cant affect each other in all
phases of the OS, including Process Scheduling, Disk Storage, and Memory
Management.
ensure reasonable response time through Swapping, in which processes are
swapped in and out of main memory to the disk.
Virtual Memory, enables users to run programs that are larger than actual
physical memory (The execution of a process is not completely in memory)
A file system that system resides on a collection of disks; hence, Disk
Management must be provided.
Provide a mechanism for protecting resources from inappropriate use.
provide mechanisms for job synchronization and communication ,and it may
ensure that jobs do not get stuck in a deadlock, forever waiting for one another.
Operating-System Operations – Interrupt Driven
Modern OS are interrupt driven, Waiting for something to
happen.
Events are almost always signalled by the occurrence of an
interrupt or trap or an exception.
Trap/Exception is a software-generated interrupt caused either
by a specific request from a user program that an OS service be
performed or by an error (div. by zero or invalid memory access,
request for OS service, infinite loop).
For each type of interrupt, separate segments of code in the
operating system determine what action should be taken (ISR).
An error in a user program could cause problems only for the
one program running.
An incorrect (or malicious) program cannot cause other
programs to execute incorrectly.
Dual Mode Operations
OS must distinguish between the execution of:
OS code ( Kernel mode or supervisor mode, system mode, or
privileged mode)
User-defined code( User mode ).
Mode bit, is added to the hardware of the computer to indicate the
current mode:
 kernel[0]: task that is executed on behalf of the OS.
 user[1]: task is executed on behalf of the user.
When a user application requests a service from the OS (via a
system call), it must transition from user to kernel.
At system boot time, the hardware starts in kernel mode. The OS
is then loaded and starts user applications in user mode.
If a trap or interrupt occurs, the HW switches from user mode to
kernel mode (changes the state of the mode bit to 0).
Thus, whenever the OS gains control of the computer, it is in
kernel mode.
The system always switches to user mode (by setting the mode
bit to 1) before passing control to a user program.
Transition from User to Kernel Mode
Timer
Make the OS must maintains control over the CPU.
Prevent a user program to get stuck in an infinite loop or to fail to
call system services and never return control to the OS.
Can interrupt the computer after a specified period fixed timer
(1/60 second) or variable timer (from 1 millisecond to 1 second).
The OS sets the counter before transfer the control to the user.
Every clock pulse, the counter is decremented. When the counter
reaches 0, an interrupt occurs (a 10-bit counter with a 1 ms
clock allows interrupts from 1 ms to 1,024 ms, in steps of 1 ms).
If the timer interrupts, control transfers automatically to the OS,
which may treat the interrupt as a fatal error or may give the
program more time.
Clearly, instructions that modify the content of the timer are
privileged.
Process Management
A process is a program in execution:
A word-processing program being run by an individual user
A system task (sending output to a printer).
Process needs resources to accomplish its task (CPU, memory,
I/O, files, Initialization data (such as file name for printing )
Process termination requires release of any reusable resources
Single-threaded process has one program counter specifying
location of next instruction to execute instructions sequentially, one at
a time, until completion
Multi-threaded process has one program counter per thread
The OS 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, process
communication and deadlock handling
Memory Management
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 activities
Keeping track of which memory locations are currently being
used and by whom.
Deciding which processes (or parts there of) and data to move
into and out of memory
Allocating and reallocating memory space as needed
Storage Management
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, datatransfer rate, access method (sequential or random)
File-System management
Mass storage management
Cashing
I/O Systems
File System Management
Is one of the most visible components of an OS.
Computers can store information on several types of physical media
( Magnetic disk, optical disk, and magnetic tape).
Each of these media has its own characteristics and physical
organization (access speed, capacity, data-transfer rate, and access
method (sequential or random)).
Each medium is controlled by a device, such as a disk drive or tape
drive.
A file is:
a collection of related information defined by its creator.
represent programs and data.
Data files may be numeric, alphabetic, alphanumeric, or binary.
Files may be free-form (for example, text files), or they may be
formatted rigidly (for example, fixed fields).
organized into directories to make them easier to use.
File System Management
When multiple users have access to files, it may be desirable to
control by whom and in what ways (for example, read, write,
append) files may be accessed.
The operating system is responsible for the following activities
in connection with file management:
Creating and deleting files and directories
Manipulate files and directories ( Open, Close , Append ,
Rename, Print, ….)
Mapping files onto secondary storage.
Backing up files on stable (nonvolatile) storage media.
Mass-Storage Management
Main memory are small to hold all data and program and data in
main memory are lost when the power is off.
Secondary storage are used as a backup for the main memory.
Most programs (compilers, assemblers, and word processors) are
stored on a disk until loaded into memory and then use the disk as
both the source and destination of their processing.
The OS is responsible for Free-space management, Storage
allocation and Disk scheduling.
Files usually organized into directories, Access control systems
determines who can access what
Some storage need not be fast
Tertiary storage includes optical storage, magnetic tape
Still must be managed – by OS or applications
Varies between WORM (write-once, read-many-times) and RW
(read-write)
Caching
Caching is an important principle of computer systems.
Information is normally kept in some storage system (such as main
memory). As it is used, it is copied into a faster storage system.
When we need a particular piece of information:
Check whether it is in the cache.
If it is, we use the information directly from the cache;
if it is not, we use the information from the source, putting a copy
in the cache under the assumption that we will need it again soon.
Without this cache, the CPU would have to wait several cycles
while an instruction was fetched from main memory.
Careful selection of the cache size and of a replacement policy can
result in greatly increased performance.
Performance of Various Levels of Storage
Migration of Integer A from Disk to Register
Movement between levels of storage hierarchy can be explicit or
implicit
I/O Subsystem
One purpose of OS is to hide difficulties of HW 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
Only the device driver knows the specialization of the specific
device to which it is assigned.
Protection and Security
Protection – a mechanism for controlling access of processes or users to
resources defined by the OS
memory-addressing hardware ensures that a process can execute only within
its own address space.
Device-control registers are not accessible to users,
an unprotected resource cannot defend against use (or misuse) by an
unauthorized or incompetent user.
Security – defense of the system against internal and external attacks
Huge range, including denial-of-service, worms, viruses, identity theft,
theft of service
OS generally must distinguish among users, to determine who can do what
User identities (user IDs ) 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
Kernel Data Structure (OS Implementation)
An array:
A simple data structure in which each element can be accessed directly.
Example,
 main
memory is constructed as an array.
 If
the data item being stored is larger than one byte, ( use multiple
bytes number × item size)
 Variable
item Sizes, ?????
Linked Lists:
the most fundamental data structures in computer science.
Each item must be accessed in a particular order.
Represents a collection of data values as a sequence.
In a singly linked list, each item points to its successor
Double linked list, a given item can refer either to its predecessor or to its
successor,
Circular linked list, the last element in the list refers to the first element,
rather than to null,
Kernel Data Structure (OS Implementation)
Kernel Data Structure (OS Implementation)
Stack:
A stack is a sequentially ordered data structure that uses the last in, first
out (LIFO) principle for adding and removing items
The operations for inserting and removing items from a stack are known
as push and pop, respectively.
Example: OS uses a stack when invoking function calls. Parameters,
local variables, and the return address are pushed onto the stack when a
function is called; returning from the function call pops those items off the
stack.
A queue,
A sequentially ordered data structure that uses the first in, first out (FIFO)
principle.
Example:
 Jobs
that are sent to a printer are typically printed in the order in
which they were submitted.
 Tasks
that are waiting to be run on an available CPU are often
organized in queues.
Kernel Data Structure (OS Implementation)
Tree:
A data structure that can be used to represent data hierarchically linked
through parent–child relationships.
A parent may have an unlimited number of children (two children for
binary tree).
Linux uses a balanced binary search tree as part its CPU-scheduling
algorithm.
Hash Function:
A hash function takes data as its input,
performs a numeric operation on this data,
and returns a numeric value. This numeric
value can then be used as an index into a
table (typically an array) to quickly retrieve the
data.
a user enters his user name and password.
The hash function is used to retrieve the
password.
Kernel Data Structure (OS Implementation)
Bitmap:
A bitmap is a string of n binary digits that can be used to represent the
status of n items.
Example, suppose we have several resources, and the availability of
each resource is indicated by the value of a binary digit: 0 means that the
resource is available, while 1 indicates that it is unavailable (or viceversa).
The value of the ith position in the bitmap is associated with the ith
resource. As an
example, consider the bitmap shown below:
» 001011101
A medium-sized disk drive might be divided into several thousand
individual units, called disk blocks.
A bitmap can be used to indicate the availability of each disk block.
Distributed Computing – Computer Network
Collection of separate,
networked together
possibly
heterogeneous,
systems
Network is a communications path
Networks vary by the protocols used, the distances between
nodes, and the transport media, their performance and
reliability.
–
Local Area Network (LAN) room, floor , building.
–
Wide Area Network (WAN) building, cities , countries
–
Metropolitan Area Network (MAN) building within a city
A network OS provides:
File sharing across the network and that includes a
communication scheme that allows different processes on
different computers to exchange messages.
Different OS communicate closely enough to provide the illusion
that only a single operating system controls the network.
Special-Purpose Systems - RTOS
Real-time embedded systems:
Embedded computers is a HW device with special purpose OS
(car engines and manufacturing robots, microwave ovens, …).
Have a specific task.
It’s OS provides limited functions
It may use a general PC with standard OS to run a special App.
Have little or no user interface.
HW device with App Specific Integrated Circuits (ASIC)
A real-time system is often used as a control device in a dedicated
application.
 Sensors
 The
bring data to the computer.
computer must analyze the data and possibly adjust
controls to modify the sensor inputs.
Special-Purpose Systems – Multimedia Systems
Most OS’s are designed to handle:
 Conventional
data (text files, programs, word documents, and
spreadsheets)
 Multimedia
data (audio and video files, video frames). These
data must be delivered (streamed) according to certain time
restrictions ( 30 f/s).
Multimedia systems:
A
wide range of applications that include audio files such as
MP3, DVD movies, video conferencing, and short video clips of
movie, live webcasts (broadcasting over the Web) of speeches
or sporting events and even live webcams.
 Includes
a combination of audio and video. For example, a
movie may consist of separate audio and video tracks.
 Exist
in desktop PC’s. PDAs and cellular telephones.
Special-Purpose Systems - Handheld systems
Personal digital assistants (PDAs), and cellular telephones use
special-purpose embedded OS.
Developers of handheld systems and applications face many
challenges due to the limited size of these devices:
 Size,
most handheld devices have small amounts of memory, slow
processors, and small display.
 CPU’s
for most handheld devices run at a fraction of the speed of a
CPU in a PC (consume less power, have no large battery).
A
lack of physical space limits input methods to small KB,
handwriting recognition, or small screen-based KB’s.
 The
small display screens limit output options (3 inch square).
 Web
clipping, only a small subset of a Web page is delivered and
displayed on the handheld device.
 use
wireless technology, such as Bluetooth, allowing remote access
to e-mail and Web browsing.
Computing Environments
How computer-system organization and major OS’s
components are used in a variety of computing environments.
Traditional Computing
Client server computing
Peer to Peer computing
Web Based Computing
Computing Environments
Traditional Computing ( an office)
Consists of PCs connected to a network, with servers providing
file and print services.
Remote access desktop.
Terminals attached to mainframes.
Portability was achieved by use of Laptop computers.
Web technology resizes the boundary.
Portals, provide Web accessibility to their internal servers.
Network computers are essentially terminals that understand
Web-based computing.
Handheld PDAs can also connect to wireless networks to use the
company’s Web portal
Home computers serve up Web pages and run networks that
include printers, client PCs, and servers.
Firewalls to protect their networks from security warms.
Computing Environments : Mobile Computing
Refers to computing on handheld smartphones and tablet computers.
Portable and lightweight, Rich functionality that is either unavailable or
impractical on a desktop or laptop computer.
Are used for e-mail, web browsing ,playing music and video, reading
digital books, taking photos, and recording HD Video, playing games.
Developers are now designing mobile APPS:
Use GPS chips, accelerometers, and gyroscopes.
An embedded GPS chip allows a mobile device to use satellites to
determine its precise location on earth.
GPS is useful in designing navigation applications (telling users
which way to walk or drive or perhaps directing them to nearby
services, such as restaurants).
An accelerometer allows a mobile device to detect its orientation with
respect to the ground and to detect certain other forces, such as tilting
and shaking.
Two OS dominate mobile computing: Apple iOS (run on Apple
iPhone and iPad mobile devices.)
Computing Environments : Distributed Systems
A distributed system is a collection of physically separate, possibly
heterogeneous, computer systems that are networked to provide
users with access to the various resources that the system maintains.
Increases computation speed, functionality, data availability, and
reliability.
Some OS generalize network access as a form of file access, with the
details of networking contained in the network interface’s device
driver.
Others make users specifically invoke network functions. Generally,
systems contain a mix of the two modes—for example FTP.
Computing Environments : Client-Server Computing
A set of PC’s connected to a centralized systems.
The centralized system acts as computer servers or file servers to
satisfy requests generated by client systems.
compute-server system:
Provides an interface to a client that can send a request to perform an
action (read data); the server executes the action and sends back
results to the client. (A server running a database that responds to client
requests for data).
The file-server system:
Provides a file-system interface where clients can create, update, read,
and delete files ( Web server delivers files to clients running Web
browsers).
Computing Environments: Peer to Peer Computing
All nodes are identical, and each of them can act as client or server,
depend on it have a request or provide a service.
Services can be provided by several nodes distributed throughout the
network, in client server model a server has a bottleneck.
Once a node has joined the network, it can begin providing services to and
requesting services from—other nodes in the network.
➢ When a node joins a network, it registers its service with a centralized
lookup service on the network. Any node desiring a specific service first
contacts this centralized lookup service to determine which node
provides the service.
➢ A client peer broadcasting a request for the service to all other nodes in
the network. The node (or nodes) providing that service responds to the
peer making the request.
Computing Environments (Cont.)
Web Based Computing
Web computing has increased the emphasis on networking.
Devices that were not previously networked now include
wired or wireless access. Devices that were networked
now have faster network connectivity, provided by either
improved networking technology, optimized network
implementation code, or both.
The implementation of Web-based computing has given rise
to new categories of devices, such as load balancers,
which distribute network connections among a pool of similar
servers.
Computing Environments (Cont.)
Virtualization
Virtualization is a technology that allows operating systems
to run as applications within other operating systems.
Virtualization is one member of a class of software that also
includes emulation.
Computing Environments (Cont.)
Cloud Computing
Cloud computing is a type of computing that delivers
computing, storage, and even applications as a service
across a network.
In some ways, it’s a logical extension of virtualization,
because it uses virtualization as a base for its functionality.
Example, the Amazon Elastic Compute Cloud (EC2) facility
has thousands of servers, millions of virtual machines, and
petabytes of storage available for use by anyone on the
Internet.
Users pay per month based on how much of those
resources they use.
Computing Environments (Cont.)
Computing Environments (Cont.)
Cloud Computing
Public cloud—a cloud available via the Internet to anyone
willing to pay for the services
Private cloud—a cloud run by a company for that company’s
own use
Hybrid cloud—a cloud that includes both public and private
cloud components
Software as a service (SaaS)—one or more applications
(such as word processors or spreadsheets) available via the
Internet
Platform as a service (PaaS)—a software stack ready for
application use via the Internet (for example, a database
server)
Infrastructure as a service (IaaS)—servers or storage
available over the Internet (for example, storage available for
making backup copies of production data)
Open-Source Operating Systems
Computer and software companies eventually sought to limit
the use of their software to authorized computers and
customers by releasing only the binary files compiled from the
source code, rather than the source code itself ( to save their
ideas from their competitors).
Counter to the copy protection and Digital Rights
Management (DRM) movement
Started by Free Software Foundation (FSF) (encouraging the
free exchange of software source code and the free use of that
software), which has “copy left” GNU Public License (GPL)
Source code can be compiled and deployed to a binary code
format to be executed on a system,
Reverse Engineering is to reach to the source code from the
binary code.
Open-Source Operating Systems
Open-source OS are those made available in source-code format
(Linux is the most famous) rather than as compiled binary code
(Closed source) Microsoft Windows is a well-known example of the
opposite closed source approach.
Benefits :
learning operating systems by examining the actual source code.
OS can be modified and compiled again (excellent learning tool).
Large community of interested programmers who contribute to the
code by helping to debug it, analyze it, provide support, and
suggest changes.
more secure than closed-source code because many more eyes
are viewing the code.
Any bug can be founded and fixed faster.
Linux Operating Systems
As an example of an open-source OS.
Produced many tools, including compilers, editors, and utilities.
Linus Torvalds, released a rudimentary UNIX-like kernel using the GNU
compilers and tools and invited contributions worldwide programmers to
download the source code, modify it, and submit changes to Torvalds.
Releasing updates once a week allowed this so-called Linux operating
system to grow rapidly, enhanced by several thousand programmers.
The resulting GNU/Linux operating system has hundreds numbers of
unique distributions, or custom builds, of the system. Major
distributions include RedHat, SUSE, Fedora, Debian, Slackware, and
Ubuntu.
Distributions vary in function, utility, installed applications, hardware
support, user interface, and purpose. For example, RedHat Enterprise
Linux is geared to large commercial use.
PCLinuxOS is a LiveCD , LiveDVD—an operating system that can be
booted and run from a CD-ROM without being installed on a system’s
hard disk.
Linux Operating Systems
Ubuntu Linux. Ubuntu is a popular Linux distribution that comes in a
variety of types, including those tuned for desktops, servers, and
students.
The following steps outline a way to explore the Ubuntu kernel source
code on systems that support the free “VMware Player” tool:
1.
Download the player from http://www.vmware.com/download/player/
and install it on your system.
2.
Download a virtual machine containing Ubuntu. are available from
VMware at http://www.vmware.com/appliances/.
3.
Boot the virtual machine within VMware Player.
4.
Get the source code of the kernel release of interest, such as 2.6, by
executing
wget
http://www.kernel.org/pub/linux/kernel/v2.6/linux2.6.18.1.tar.bz2 within the Ubuntu virtual machine.
Uncompress and untar the downloaded file via tar xjf linux2.6.18.1.tar.bz2.
Explore the source code of the Ubuntu kernel, which is now in ./linux2.6.18.1.
End of Chapter 1