1. Chapter 1: Introduction

2. Chapter 1: Introduction
What Operating Systems Do
Computer-System Organization
Computer-System Architecture
Operating-System Structure
Operating-System Operations
Process Management
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.
Handheld computers (Single user & may connected to networks)
Their operating systems are designed mostly for individual usability and performance per unit of battery life is important as well.
Embedded computers
If the computers have little or no user view, OS is designed primarily to run without user intervention (minimize usability)

8. The operating system’s Role (cont.)
System View:
OS is a resource allocator
Manages all resources (e.g. CPU time, memory space, file-storage space, I/O devices…etc)
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
Operating System Definition:
It is a software that manage the computer hardware and provide an environment for application programs to run
“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

10. Computer-System Organization
Computer-System Operation
Storage Structure
I/O Structure

11. Computer System Organization
Computer-system operation
A general-purpose computer system consists of
One or more CPU
Multiple device controllers that are connected through a common bus
RAM connecting to CPU and device controllers through common bus
Each device controller is responsible of a specific type of device (e.g. disk drives, audio devices, and video displays).
The CPU and the device controllers can execute concurrently, competing for memory cycles . So, a memory controller is provided whose function is to synchronize access to the memory.

12. Computer-system operation

13. 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
ROM : read-only memory,
computer memory on which data has been prerecorded.
Once data has been written onto a ROM chip, it cannot be removed and can only be read.
EEPROM: electrically erasable programmable read-only memory.
EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge.
EEPROM retains its contents even when the power is turned off.
firmware: Firmware is software that is embedded in a piece of hardware.
You can think of firmware simply as "software for hardware.“
Typical examples of devices containing firmware are embedded systems (such as traffic lights,
consumer appliances, mobile phones, and digital cameras )
The firmware contained in these devices provides the control program for the device.
Firmware is held in non-volatile memory

14. Computer System Operation (cont.)
Interrupt:
It is a signal that gets the attention of the CPU
It generated 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.
A trap is a software-generated interrupt caused either by an error or a user request
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 when I/O is required.

15. Storage Structure
Main memory – only large storage media that the CPU can access directly
Secondary storage – extension of main memory that provides large nonvolatile storage capacity
Magnetic disks – rigid metal or glass platters covered with magnetic recording material
Disk surface is logically divided into tracks, which are subdivided into sectors
The disk controller determines the logical interaction between the device and the computer

16. Storage Structure (cont.)
All forms of memory provide an array of words. Each word has its own address.
Interaction is achieved through a sequence of load or store instructions to specific memory addresses.
The load instruction>>> moves a word from RAM to CPU’s register
The store instruction>>> moves the content of a CPU’s register to RAM
CPU automatically loads instructions from main memory for execution.

17. Storage Structure (cont.)
Typical instruction-execution cycle :
Fetches an instruction from memory and stores that instruction in the instruction register .
The instruction is decoded and may cause operands to be fetched from memory and stored in some internal register.
the instruction on the operands is executed
the result may be stored back in memory.

18. Storage Structure (cont.)
Storing programs and data in RAM permanently is impossible because:
RAM is too small to store all needed programs and data permanently.
RAM is volatile storage device that loses its contents when power is turned off.

19. Storage Hierarchy Storage systems organized in hierarchy Speed Cost
size
Volatility
Caching
It is copying information into faster storage system.
Caches can be installed to improve performance where a large access-time or transfer-rate disparity exists between two components.
The design of a complete memory system must balance all the factors just discussed:
It must use only as much expensive memory as necessary while providing as much inexpensive, nonvolatile memory as possible.

20. Storage-Device Hierarchy
More expensive and faster
volatile
can be volatile or non volatile
Non-volatile

21. I/O Structure
Storage (e.g. hard disk) is only one of many types of I/O devices within a computer.
A large portion of OS code is dedicated to managing I/O, because of:
Its importance to the reliability and performance of a system
The varying nature of the devices.

22. I/O Structure (cont.)
A device controller maintains some local buffer storage and a set of special-purpose registers.
The device controller is responsible for moving the data between the peripheral devices that it controls and its local buffer storage.
Operating systems have a device driver for each device controller. This device driver understands the device controller

23. I/O Structure (cont.) Typical I/O operation: (method #1)
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 (such as “read “a character from the keyboard”).
The controller starts the transfer of data from the device to its local buffer.
Once the transfer of data is complete, the device controller informs the device driver via an interrupt that it has finished its operation.
The device driver then returns control to the operating system, possibly returning the data or a pointer to the data if the operation was a read.
This form of interrupt-driven I/O is fine for moving small amounts of data but can produce high overhead when used for bulk data movement such as disk I/O.

24. I/O Structure (cont.) Direct memory access I/O operation: (method #2)
This method is used to solve the problem of moving bulk data without causing OS overhead >>>> (to improve performance)
What is direct memory access (DMA) ?
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, rather than the one interrupt per byte generated for low-speed devices.
While the device controller is performing these operations, the CPU is available to accomplish other work.

25. Computer-System Architecture
Single-processor systems
It has one CPU capable of executing a general-purpose instruction set, including instructions from user processes.
Most systems use a single processor (PDAs through mainframes)
Almost all systems have other special-purpose processors
The use of special-purpose microprocessors is common and does not turn a single-processor system into a multiprocessor.

26. Computer-System Architecture
About special-purpose processors :
They may come in the form of device-specific processors, such as disk, keyboard controllers
Special-purpose processors run a limited instruction set and do not run user processes.
Special-purpose processors types:
Managed by the operating system—
e.g. A disk-controller microprocessor receives a sequence of requests from CPU and implements its own disk queue and scheduling algorithm).
This arrangement relieves CPU of the overhead of disk scheduling (advantage)
special-purpose processors that are low-level components built into the hardware.
Os cannot communicate with these processors; they do their jobs autonomously.

27. Computer-System Architecture
MULTIPROCESSOR SYSTEMS
Also known as parallel systems, tightly-coupled systems
have two or more processors in close communication, sharing the computer bus and some times the clock, memory, and peripheral devices.
Advantages include:
Increased throughput
more work is performed
Economy of scale
Multiprocessor systems can cost less than equivalent multiple single-processor systems, because they can share peripherals, mass storage, and power supplies.
Increased reliability
the failure of one processor will not halt the system, only slow it down.

28. Computer-System Architecture
MULTIPROCESSOR SYSTEMS – (CONT.):
Two types
Asymmetric Multiprocessing
Each processor is assigned a specific task.
master-slave relationship
A master processor controls the system; It schedules and allocates work to the slave processors.
Symmetric Multiprocessing (SMP)
Each processor performs all tasks within the operating system.
All CPUs are peers
Each processor has its own set of registers & cache
All processors share physical memory.

29. Symmetric Multiprocessing Architecture

30. Computer-System Architecture
SMP pros (++):
many processes can run simultaneously —N processes can run if there are N CPUs—without causing a significant deterioration of performance
SMP Cons (--):
OS must carefully control I/O to ensure that the data reach the appropriate processor.
since the CPUs are separate, one may be sitting idle while another is overloaded, resulting in inefficiencies.
All modern operating systems—including Windows, Mac OS X, and Linux—now provide support for SMP.

31. Computer-System Architecture
Multi-cores chips.
It is a recent trend in CPU design is to include multiple computing cores on a single chip.
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
Multi-cores chips can be more efficient than multiple chips with single cores because:
on-chip communication is faster than between-chip communication
one chip with multiple cores uses significantly less power than multiple single-core chips.

32. A Dual-Core Design
Dual-core processor contains two cores (Such as Intel Core Duo).
Multi-core systems are especially well suited for server systems such as database and Web servers.

33. Computer-System Architecture
Clustered Systems:
they are systems composed of two or more individual systems linked together. ……(definition)
Represent another type of multiple-CPU system
Like multiprocessor systems, clustered systems have multiple CPUs
Clustered systems differ from multiprocessor systems, in that they are composed of two or more individual
Clustering is usually used to provide high-availability service.
service will continue even
if one or more systems in
the cluster fail

34. Operating System Structure
Multiprogramming environment:
Single program cannot keep CPU and I/O devices busy at all times
Multiprogramming increases CPU utilization by organizing jobs (code and data) so that the CPU always has one to execute.
Multiprogramming idea is as follows:
The operating system keeps several jobs in memory simultaneously .
One job selected and run via job scheduling.
When it has to wait (for I/O for example), OS switches to another job
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.
RAM is too small to accommodate all jobs, the jobs are kept initially on the disk in the job pool.
This pool consists of all processes residing on disk awaiting allocation of main memory.

35. Memory Layout for Multiprogrammed System

36. Operating System Structure
Time sharing (or multitasking) system:
It 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
The response time should be short ( less than one second)
amount of time it takes from
when a request was submitted
until the first response is
produced.
system that provides direct
communication between the
user and the system.

37. Operating System Structure
A time-shared operating system allows many users to share the computer simultaneously. each user is given the impression that the entire computer system is dedicated to his use.
Each user has at least one separate program in memory.
A process : is a program loaded into memory and executing

38. Computing Environments
Traditional Computing
Client–Server Computing
Peer-to-Peer Computing
Web-Based Computing

39. Computing Environments
Traditional computing
Office environment
In past >>>
PCs connected to a network or terminals attached to mainframe
Remote systems access was difficult
Portability was achieved by using laptops
Now>>>
Web portals allowing remote systems access
Hand-held computers are used to provide portability
Wireless networks is more common and efficient
Home environment
In past >>> Used to be single computer, with slow modem
Now >>> multiple computers with fast inexpesive internet connection

40. Computing Environments (Cont)
Client-Server Computing
Dumb terminals supplanted by smart PCs
Many systems now servers, responding to requests generated by clients
Server systems can be categorized as:
Compute-server system
provides an interface to which a client can send a request to perform an action
the server executes the action and sends back results to the client. (e.g. database servers )
File-server system
provides interface for clients to store and retrieve files

41. Computing Environments (Cont)
Client-server Structure

42. 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

43. Web-Based Computing Web has become popular PCs most prevalent devices
More devices becoming networked to allow web access (e.g. handheld PDA, smart phones….etc)
New category of devices is appeared: load balancers
The Web has increased the complexity of devices because their users require them to be Web-enabled.
is a physical unit that directs
computers to individual servers
in a network, based on factors
such as server processor utilization

44. End of Chapter 1

45. Some Helpful Notes Some terminologies : Usability = ease of use
Utilization= efficiency
Performance= speed
Synchronize = manage the timing
System overhead = more work must be performed by the system (e.g. more load)
Distributed System: refers to multiple computer systems working on a single problem.
In distributed computing, a single problem is divided into many parts, and each part is solved by different computers.
As long as the computers are networked, they can communicate with each other to solve the problem.

46. Some Helpful Notes (cont.)
Load & store operations between RAM & CPU is different from Load & store operations between RAM & storage devices
Between RAM & CPU :
The load instruction>>> moves a word from RAM to CPU’s register
The store instruction>>> moves the content of a CPU’s register to RAM
Between RAM & Storage Devices :
The load instruction>>> moves a word from storage device to RAM.
The store instruction>>> moves a word from RAM to storage device .