Transcript OPERATING SYSTEM CONCEPT AND PRACTISE

OPERATING SYSTEM CONCEPT
AND PRACTISE
CSC633
INTRODUCTION
 A computer is an electronic machine which
consists of hardware and software resources.
 Hardware components refers to physical parts
of computer.
 Software means computer instructions or data
that is stored electronically on computer.
 A system refers to a complete working
computer.
 Input devices are what is used to put data into
computer example mouse, keyboard
microphone etc.
 Output devices are through which the
computer gives information to user example
printers, monitors, loudspeakers etc
 There are two types of memory in Computer:
• Primary Memory
•
Secondary Memory
 Primary memory is internal memory of
computer and provides main working space to
computer.
 Terms under Primary memory
• Random Access Memory
• Read Only Memory
• Programmable Read Only
Memory(PROM)
• Cache Memory
• Erasable Programmable Read Only
Memory(EPROM)
 Random Access Memory (RAM) is that can be
accessed randomly ,a common type of
memory found in computer and devices like
printers.
 Read Only Memory(ROM) refers to special
memory used to store programs.
• In a programmable read only memory (PROM)
programs or instructions written cannot be
changed.
• In Erasable programmable read only
memory(EPROM) chip can be written again by
erasing the information stored earlier in it.
 CPU is made up of 3 main parts :
 Arithmetic Logic Unit(ALU)
 Registers
 Control Unit
 Arithmetic Logic Unit (ALU) is a part of
computer in CPU used to perform all
arithmetic computations.
 A Register is a high speed storage area in the
CPU
 Control Unit is a component of CPU, it controls
and coordinates between input and output
devices.
 The Motherboard serves to connect all of the
parts of a computer together.
 A Motherboard is the piece of computer
hardware that can be thought of as the
“backbone” of pc.
 Main memory is where anything that the
computer is working with is kept.
 A Buffer is used for temporary storage of data
that is waiting to be sent to a device.
 A Central Processing Unit (CPU) is the most
important element of computer system
where most calculations takes place.
 The number of registers that a CPU has and
the size of each help determine the power and
speed of Central Processing Unit(CPU)
 A Register is a high-speed storage area within the
Central Processing Unit(CPU). All data must be
represented in a register before it is processed.
 The Register contains address of memory location
where data is stored.
 Sometimes the speed of CPU is high compared to
access time of main memory, therefore the
performance of CPU decreases. To decrease this
mismatch a small memory chip is attached
between CPU and main memory known as cache.
What is an Operating System?
 A program that acts as an intermediary
between a user of a computer and the
computer hardware.
 The operating system is a chief piece of
software that manages all the hardware and
software resources.
 Use the computer hardware in an efficient
manner.
 Tasks of Operating system:
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Memory Management
Human computer Interface
Error Reporting
File management
 System software is a term given to set of
computer programs that make the hardware
work properly.
Four Components of a Computer
System
 Computer system can be divided into 4
components:
 Users: People, machines, other computers
 Compiler: It is a computer program that
translates source code from a high level
programming language to a lower level
language
 An assembler is a program that takes basic
computer instructions and converts them
into a pattern of bits.
 A text editor is a type of program used for
editing plain text files
 A Database is an organized collection of
data.
 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
 Hardware provides basic computing devices
like CPU, memory, I/O devices.
 Operating System controls the use of
hardware among various applications and
users.
User View of Computer
• Most systems are designed for one user.
• Main goal is to maximize the work the user
performs.
• In some cases user is connected through a
minicomputer and other users access same
computer to exchange information.
• Some cases users sit at workstation connected
to a network of other stations
System View
• From computer's point of view, the operating
system is the program most intimately
involved with the hardware.
• Operating system is a resource allocator.
• A operating system is mainly to control
program.
COMPUTER SYSTEM ORGANIZATION
 One or more CPUs, device controllers
connect through common bus providing
access to shared memory.
 Each device controller is in charge of a
specific type of device (for example, disk
drives, audio devices, and video displays)
 Central Processing Unit known as CPU is
the hardware within the computer.
 For a computer to start running , when it is
rebooted it needs initial program named
bootstrap program.
 Bootstrap must know how to load the
operating system and start executing.
 It locates and load into memory the operating
system kernel.
 The operating system executes the first
process such as Init.
The occurrence of event is signaled by an
interrupt.
When CPU is interrupted it stops and
immediately and transfers execution to fixed
location.
The location contains starting address where
service routine is located.
 The fixed location usually contains the starting
address where the service routine for the
interrupt is located.
Common Functions of Interrupts
 Interrupt transfers control to the interrupt service
routine generally, 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 operating system is interrupt driven.
I/O Structure
 A general computer system consists of CPU
and multiple devices connected through a
common bus.
 Each device controller is in charge of a specific
type of device
 A device controller maintains some local
buffer storage and a set of special-purpose
registers.
 Operating systems have a device driver for
each device controller.
 To start a I/O operation the following steps
takes place:
 Device driver loads appropriate registers within
device controller.
 Device controller examines the contents of
registers
The controller transfers data from device to local
buffer
Once transfer is complete the device controller
informs device driver via interrupt.
Device driver returns control to OS.
 Direct Memory Access (DMA)used for highspeed 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.
COMPUTER SYSTEM OPERATION
 A trap (or an exception) is a software-generated
interrupt caused either by an error or by a
specific request from a user program that an
operating-system service be performed.
 For each type of interrupt, separate segments of
code in the operating system determine what
action should be taken.
 A properly designed operating system must
ensure that an incorrect (or malicious) program
cannot cause other programs to execute
incorrectly.
Dual-Mode Operation
 we need two separate modes of operation:
 user mode
 kernel mode
 A bit, called the mode bit, is added to the
hardware of the computer to indicate the
current mode.
 When the computer system is executing on
behalf of a user application, the system is in
user mode.
 When a user application requests a service
from the operating system it must transition
from user to kernel mode to fulfill the request.
 At system boot time, the hardware starts in
kernel mode. The operating system is then
loaded and starts user applications in user
mode.
 Whenever a trap or interrupt occurs, the
hardware switches from user mode to kernel
mode.
 The system always switches to user mode
before passing control to user program
COMPUTER SYSTEM ARCHIECTECTURE
 It can be categorized with respect to number
of processors used.
 Single-Processor System: There is one main
CPU capable of executing a general-purpose
instruction set.
 Multiprocessor Systems :Systems have two or
more processors in close communication
sharing the computer bus.
• Clustered Systems: Clustered computers share
storage and are closely linked via a local-area
network (LAN).
OPERATING SYSTEM STRUCTURE
 Important aspect of operating system is multiprogramming.
 The operating system keeps several jobs in
memory.
 The operating system picks and begins to
execute one of the jobs in memory.
 Eventually, the job may have to wait for some
task, such as an I/O operation, to complete.