Download 01-ch1_introduction_minor changes - pnu-cs-os

Princess Nora University
Faculty of Computer & Information Systems
Computer science Department
Operating Systems
(CS 340 D)
(Chapter-1)
Introduction
Chapter 1 Introduction
1. What Operating Systems Do
2. Computer-System Organization
3. Computer-System Architecture
4. Operating-System Structure
3
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.
4
What is an Operating
System?
5
What is an Operating System?
6

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

Use the computer hardware in an efficient manner
Operating System Functions






7
Process Management
Memory Management
File Management
Device Management
Command Interpretation
Security
Computer System Structure

Consists of four components
1.
Hardware : provides basic computing resources (CPU, memory, I/O devices)
2.
Operating system: Controls and coordinates (use, hardware, applications)
3.
Application programs :
“define the ways in which the system resources are used to solve the computing
problems of the users”
ex: (Word processors, compilers, web browsers, database systems, video games)
4.
Users : People, machines, other computers
8
Four Components of a Computer System
9
Four Components of a Computer System
10
The operating system’s Role
1- User View:
Category
Explanation and
Example
OS is designed to
Single User
desktop and laptop computers
ease of use
Multiple Users
mainframe or minicomputer
maximize resource utilization
Workstations users
connected to networks of
other workstations and servers.
compromise between individual
usability and resource
utilization.
Handheld computers
individual users and they are
connected to networks through
cellular or other wireless
technologies.
individual usability and
performance per unit of
battery life is important as well.
Embedded
computers
If the computers have little or no
user view
run without user intervention
(minimize usability)
11
The operating system’s Role (cont.)
2- System View:
OS is a resource allocator
OS is a control program
• Manages all resources (e.g.
CPU time, memory space,
• Controls execution of
file-storage space, I/O
programs to prevent errors
devices…etc)
• Decides between conflicting
requests of many users
access the same mainframe
or minicomputer
12
• It is especially concerned
with the operation and
control of I/O devices.
Operating System Definition
Operating System Definition:
It is a software that manage the computer hardware and provide an
environment for application programs to run
 A more common definition:
“The one program running at all times on the computer” usually called
the kernel.
 What constitutes an OS?
Kernel
 system program
application program

13
Computer-System
Organization
14
Computer-System Organization
1. Computer-System Operation
2. Storage Structure
3. I/O Structure
15
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.
A general-purpose computer system
Computer System Organization
1-Computer-system operation(cont..)
Computer Startup:

bootstrap program is loaded at power-up or reboot
 Typically stored in ROM, generally known as firmware
 Initializes all aspects of system
 Loads operating system kernel and starts execution
ROM : read-only memory, Once data has been written onto a ROM chip,
it cannot be removed and can only be read.
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, and digital cameras )
•The firmware contained in these devices provides the control program for the device.
•Firmware is held in non-volatile memory
18
Computer System Organization
1-Computer-system operation(cont..)
The interrupt is signal that gets the attention of the CPU and is usually
generated when I/O is required.

It generated from either the hardware or the software
 Hardware  sending a signal to the CPU through system bus.
 Software by executing a special operation called a system call.
For example:
• Interrupt driven by hardware ( e.g. when a key is pressed or when the mouse
is moved).
• Software interrupts are generated by a program when I/O is required.
Software error or request creates exception or trap ( e.g. division by zero,
request for operating system service )
A trap is a software-generated interrupt caused either by an error or a user request
• Other process problems include infinite loop, processes modifying each other
or the operating system
19
Computer System Organization
1-Computer-system operation(cont..)
Dual-Mode and Multimode Operation




user mode
kernel mode (also called supervisor mode, system mode, or privileged
mode).
Dual-mode operation allows OS to protect itself and other system
components
Mode bit provided by hardware
 Provides ability to distinguish when system is running user code or
kernel code
 Some instructions designated as privileged, only executable in kernel
mode
 System call changes mode to kernel, return from call resets it to user
Transition from User to Kernel Mode
21
Computer System Organization
2-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
22
Computer System Organization
More expensive and faster
2-Storage Structure (cont..)
23
volatile
can be volatile
or non volatile
Nonvolatile
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:

24
It must use only as much expensive memory as necessary while providing as much inexpensive,
nonvolatile memory as possible.
Computer System Organization
2-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.
25
Storage Structure (cont.)

Typical instruction-execution cycle :
1.
2.
3.
4.
26
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.
Storage Structure (cont.)

Storing programs and data in RAM permanently is impossible
because:


27
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.
Computer System Organization
3-I/O Structure

A large portion of OS code is dedicated to managing I/O,
because of:


28
Its importance to the reliability and performance of a system
The varying nature of the devices.
Computer System Organization
3-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
29
Computer System Organization
3-I/O Structure(cont..)
DC : Responsible for moving data between
Device
Controller (DC)
Peripherals devices
that it controls eg:
keyboard
Local buffer
storage
Understand
how?
OS
30
Device Driver
(DD)
+
Set of special
purpose
registers
I/O Structure (cont.)

Typical I/O operation: (method #1)






31
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.
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) ?



32
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.
Computer-System
Architecture
33
Computer-System Architecture

Single-processor systems :

MULTIPROCESSOR SYSTEMS
have two or more processors in close communication, sharing the
computer bus and some times the clock, memory, and peripheral
devices..
34
one CPU
Computer-System Architecture

Single-processor systems




35
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.
Computer-System Architecture

36
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.
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:
1. Increased throughput

2.
Economy of scale

3.
Multiprocessor systems can cost less than equivalent multiple singleprocessor systems, because they can share peripherals, mass storage,
and power supplies.
Increased reliability

37
more work is performed
the failure of one processor will not halt the system, only slow it
down.
Computer-System Architecture (cont..)

MULTIPROCESSOR SYSTEMS TYPES – (CONT.):
Asymmetric
Multiprocessing
o Each processor is assigned a
specific task.
o master-slave relationship
o A master processor controls
the system; It schedules and
allocates work to the slave
processors.
38
Symmetric Multiprocessing
(SMP)
o Each processor performs all tasks within
the operating system. (peer =equal rank)
o Each processor has its own set of
registers & cache
o All processors share physical memory.
Symmetric Multiprocessing Architecture
39
Computer-System Architecture (cont..)
 SMP

pros (++):
many processes can run simultaneously —N processes can run if there are N
CPUs—
 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.
40
Computer-System Architecture (cont..)
o
o
o

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 process only
one instruction at a time.
Multi-cores chips.
o
It is a recent trend in CPU design is to
include multiple computing cores on
a single chip.
41
A Dual-Core Design
oMulti-cores chips can be
more efficient than multiple
chips with single cores
because:
1.
Dual-core
processor contains two
cores (Such as Intel Core Duo).
Multi-core
systems are especially
suited for server systems such as
database and Web servers.
42
on-chip communication is
faster than between-chip
communication
2. one chip with multiple cores
uses significantly less power
than multiple single-core
chips.
Operating System Structure
43
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:





44
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.
Memory Layout for Multiprogrammed System
45

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.
Operating System Structure

Time sharing (or multitasking) system:
 It is a logical extension of multiprogramming.





46
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.
The CPU time is shared by different processes, so it is called as “Time
sharing Systems”.
Time slice is defined by the OS, for sharing CPU time between
processes.
CPU is taken away from a running process when the allotted time slice
expires.
Eg.: Unix, etc
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
47
Thank you
End of
Chapter 1
48
Some Helpful Notes

Some terminologies :





49
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)
Some Helpful Notes (cont.)

Load & store operations between RAM & CPU is different
from Load & store operations between RAM & storage
devices


50
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
:
moves a word from storage device to RAM.

The load instruction>>>

The store instruction>>> moves a word from RAM to storage device .