Operating System
chapter 1 : Introduction to OS
Computer System divided into 4 components:
1. Hardware : cpu,memory,I/O devices
2. Opreating System : controls use of Hardware
3. Application programs
4. Users
Define OS : is a program manages computer’s hardware and acts as
interface (intermediate) between user and hardware
OS goals:
• Execute user programs and make solving problems easier
• Make the Computer System convenient to use ( )سهل االستخدام
• Use the computer hardware in an efficient manner
What OS do ?
According to:
• User view : Users want convenience()سهولة, ease of use and good
performance
• Don’t care about resourse utilization
• System view: Must involved with hardware , we can view an OS as
resourse allocator => manages all resources
OS is control program => controls execution of programs to prevent errors
Kernel : is one program running at all times on the computer
• The core of OS ( OS)هو النواة بتاعه ال
With kernel we have two types of programs run with :
• System programs : which are associated with OS but not necessary
part of kernel
• Application programs : which include all programs not associated
with OS
Computer Startup ( )لما اجى اشغل الكمبيوتر:
Bootstrap : program is loaded at power up or reboot
• Typically stored in ROM or EPROM generally know as Firmware
• Initializes all aspects of system
• Load OS kernel and start execution
Interrupts ()المقاطعات:
• OS is Interrupt driven
• The occurrence of an event is usually signaled by interrupt from
either Hardware or Software
• Hardware may trigger ( )يستدعىan interrupt at any time by sending a
signal to cpu
• Software may trigger an interrupt by executing a special operation
called a System Calls
• Interrupts are important part of a computer archeticture
• A trap ot Exception : is a software genrated interrupt caused by an
error or user request
Storage Structure:
Basic unit of computer storage is bit
Storage divided into :
• Main Memory : CPU can access directly such as RAM (volatile )مؤقتة
• Secondary Storage : Large and non-volatile such as Hard disk
Storage System organized in hierarchy:
Registers → cache → main memory → solid-state disk (SSD) → hard disk →
optical disk → magnetic types
• كل اما امشى يمين بتقل التكلفة و تقل السرعة و تزيد المساحة
(Less cost , Less speed , More Storage)
Multiprocessors System : growing in use and importance
• Also known as parallel systems
Advantages:
• Increased Throughtput : get more work done in less time
• Economy of Scale : can cost less than equivalent multi-single process
systems
• Increased Reliability : graceful degradation ( )رشيقة التدهورor fault
tolerance ()التسامح مع الخطا
Multiprocessors has two types :
1. Asymmetric → each processor is assigned a specific task
2. Symmetric → each processor performs all tasks
Multichip and Multicore :
• One processor has multi-cores such as core i3 , core i5 , core i7
Multiprogramming (Batch System) :
• organizes jobs so cpu always has one to execute via (Job Scheduling)
TimeSharing (Multitasking) :
• is logical extension in which cpu switches jobs so the user can
interact with each job while it is running
Dual-Mode operation : allows OS to protect itself and other system
components
We have Two modes :
• User Mode
• Kernel Mode
System calls switch from user mode to kernel mode
Protection → any mechanism for controlling access of processes or users
resources defined by OS
Security → defense of the system against internal and external attacks
Network :
Portals : which provides web access to their internal services
Network Computers : which are essentially terminals that understand web
based computing
Network is communication path TCP / IP most common
Types of Computer Networks : LAN , WAN , MAN , PAN
Network OS : provides features between system across network
Mechanism → How to do something ?
Policy → what you have be done ?
Virtualization → is a technology that allows OS to run as application within
other OS
• VMM(virtual machine manager) : provides virtualizations services
Cloud Computing :
• Delivers computing , storage , even apps as a service across network
Divided into :
• Public Cloud : available by anyone willing to pay
• Private Cloud : run by a company for the company’s own use
• Hyprid Cloud : includes both puplic and private cloud components
We have Three Types of Cloud Computing :
1. Software as a Service (SaaS) : One or more apps available via internet
sush as (Word processor)
2. Platform as a Service (PaaS) : Software stack ready for apps use via
internet such as (database server)
3. Infrastructure as a Service(IaaS) : Servers or Storage available over
internet such as (Storage for backup)
Chapter 1 Finished
