CST 206 OPERATING SYSTEMS
MODULE 1
Introduction: Operating system overview – Operations, Functions, Service – System calls,
Types – Operating System structure - Simple structure, Layered approach, Microkernel,
Modules – System boot process.
WHAT IS AN OPERATING SYSTEM?
An operating system acts as an intermediary between the user of a computer and computer hardware.
The purpose of an operating system is to provide an environment in which a user can execute programs in
a convenient and efficient manner.
Operating System
• An operating system is a program that controls the execution of application programs .A more
common definition is that the operating system is the one program running at all times on the
computer (usually called the kernel), with all else being system program (ships with the operating
system) or application programs.
• An operating system is concerned with the allocation of resources and services, such as memory,
processors, devices, and information. The operating system correspondingly includes programs to
manage these resources, such as a traffic controller, a scheduler, memory management module, I/O
programs, and a file system.
• An operating system is software that manages the computer hardware. The hardware must provide
appropriate mechanisms to ensure the correct operation of the computer system and to prevent
user programs from interfering with the proper operation of the system
• OS is a System Software. Computer system can be divided into four components:
1. Hardware – provides basic computing resources example: CPU, memory, I/O devices.
2. Operating system-Controls and coordinates use of hardware among various applications and users.
3. Application programs – define the ways in which the system resources are used to solve the
computing problems of the users. Examples: Word processors, compilers, web browsers, database
systems, video games
4. Users-People, machines, other computers
Figure 1.1 Abstract view of the components of a computer system
1
, CST 206 OPERATING SYSTEMS
❑ User View
❖ Single users: ease of use
❖ Mainframe or a minicomputer-to maximize resource utilization
❖ Workstations connected to networks of other workstations and servers.
❑ System View
❖ OS is a resource allocator
❖ Manages all resources
❖ Decides between conflicting requests for efficient and fair resource use
❖ OS is a control program
❖ Controls execution of programs to prevent errors and improper use of the computer.
FEATURES OF AN OPERATING SYSTEM
1. Convenience: An OS makes a computer more convenient to use.
2. Efficiency: An OS allows the computer system resources to be used in an efficient manner.
3. Ability to Evolve: An OS should be constructed in such a way as to permit the effective development,
testing and introduction of new system functions at the same time without interfering with service.
BASICS OF OPERATING SYSTEM(COMPUTER SYSTEM OPERATION)
A modern general-purpose computer system consists of one or more CPUs and a number of device
controllers connected through a common bus that provides access to shared memory.
Figure 1.2 A modern computer system
❖ Each device controller is in charge of a specific type of device.
❖ The CPU and the device controllers can execute concurrently ,competing for memory cycles.
❖ To ensure orderly access to the shared memory, a memory controller is provided whose function is
to synchronize access to the memory.
Storage Definitions and Notations
• The basic unit of computer storage is the bit.
• A bit can contain one of two values, 0 and 1.
• All other storage in a computer is based on collections of bits.
• Given enough bits, it is amazing how many things a computer can represent: numbers, letters,
images, movies, sounds, documents, and programs, to name a few.
• A byte is 8 bits, and on most computers it is the smallest convenient chunk of storage.
2
, CST 206 OPERATING SYSTEMS
• A less common term is word, which is a given computer architecture’s native unit of data. A word is
made up of one or more bytes.
• Computer storage is generally measured and manipulated in bytes and collections of bytes.
A kilobyte, or KB, is 1,024 bytes
a megabyte, or MB, is 1,0242 bytes
a gigabyte, or GB, is 1,0243 bytes
a terabyte, or TB, is 1,0244 bytes
a petabyte, or PB, is 1,0245 bytes
Fig 1.3: Storage Device Hierarchy
OPERATING-SYSTEM OPERATIONS
• Modern operating systems are interrupt driven.
• Events are almost always signaled by the occurrence of an interrupt or a trap.
• A trap (or an exception) is a software-generated interrupt caused either by an error (for example,
division by zero or invalid memory access) or by a specific request from a user program that an
operating-system service be performed.
1. Dual-Mode and Multimode Operation
• We need two separate modes of operation: user mode and kernel mode (also called supervisor
mode, system mode, or privileged mode). A bit, called the mode bit, is added to the hardware of the
computer to indicate the current mode: kernel (0) or user (1).
• With the mode bit, we can distinguish between a task that is executed on behalf of the operating
system and one that is executed on behalf of the user.
• When the computer system is executing on behalf of a user application, the system is in user mode.
However, when a user application requests a service from the operating system (via a system call),
the system must transition from user to kernel mode to fulfill the request.
2. Timer
• We must ensure that the operating system maintains control over the CPU.
3
MODULE 1
Introduction: Operating system overview – Operations, Functions, Service – System calls,
Types – Operating System structure - Simple structure, Layered approach, Microkernel,
Modules – System boot process.
WHAT IS AN OPERATING SYSTEM?
An operating system acts as an intermediary between the user of a computer and computer hardware.
The purpose of an operating system is to provide an environment in which a user can execute programs in
a convenient and efficient manner.
Operating System
• An operating system is a program that controls the execution of application programs .A more
common definition is that the operating system is the one program running at all times on the
computer (usually called the kernel), with all else being system program (ships with the operating
system) or application programs.
• An operating system is concerned with the allocation of resources and services, such as memory,
processors, devices, and information. The operating system correspondingly includes programs to
manage these resources, such as a traffic controller, a scheduler, memory management module, I/O
programs, and a file system.
• An operating system is software that manages the computer hardware. The hardware must provide
appropriate mechanisms to ensure the correct operation of the computer system and to prevent
user programs from interfering with the proper operation of the system
• OS is a System Software. Computer system can be divided into four components:
1. Hardware – provides basic computing resources example: CPU, memory, I/O devices.
2. Operating system-Controls and coordinates use of hardware among various applications and users.
3. Application programs – define the ways in which the system resources are used to solve the
computing problems of the users. Examples: Word processors, compilers, web browsers, database
systems, video games
4. Users-People, machines, other computers
Figure 1.1 Abstract view of the components of a computer system
1
, CST 206 OPERATING SYSTEMS
❑ User View
❖ Single users: ease of use
❖ Mainframe or a minicomputer-to maximize resource utilization
❖ Workstations connected to networks of other workstations and servers.
❑ System View
❖ OS is a resource allocator
❖ Manages all resources
❖ Decides between conflicting requests for efficient and fair resource use
❖ OS is a control program
❖ Controls execution of programs to prevent errors and improper use of the computer.
FEATURES OF AN OPERATING SYSTEM
1. Convenience: An OS makes a computer more convenient to use.
2. Efficiency: An OS allows the computer system resources to be used in an efficient manner.
3. Ability to Evolve: An OS should be constructed in such a way as to permit the effective development,
testing and introduction of new system functions at the same time without interfering with service.
BASICS OF OPERATING SYSTEM(COMPUTER SYSTEM OPERATION)
A modern general-purpose computer system consists of one or more CPUs and a number of device
controllers connected through a common bus that provides access to shared memory.
Figure 1.2 A modern computer system
❖ Each device controller is in charge of a specific type of device.
❖ The CPU and the device controllers can execute concurrently ,competing for memory cycles.
❖ To ensure orderly access to the shared memory, a memory controller is provided whose function is
to synchronize access to the memory.
Storage Definitions and Notations
• The basic unit of computer storage is the bit.
• A bit can contain one of two values, 0 and 1.
• All other storage in a computer is based on collections of bits.
• Given enough bits, it is amazing how many things a computer can represent: numbers, letters,
images, movies, sounds, documents, and programs, to name a few.
• A byte is 8 bits, and on most computers it is the smallest convenient chunk of storage.
2
, CST 206 OPERATING SYSTEMS
• A less common term is word, which is a given computer architecture’s native unit of data. A word is
made up of one or more bytes.
• Computer storage is generally measured and manipulated in bytes and collections of bytes.
A kilobyte, or KB, is 1,024 bytes
a megabyte, or MB, is 1,0242 bytes
a gigabyte, or GB, is 1,0243 bytes
a terabyte, or TB, is 1,0244 bytes
a petabyte, or PB, is 1,0245 bytes
Fig 1.3: Storage Device Hierarchy
OPERATING-SYSTEM OPERATIONS
• Modern operating systems are interrupt driven.
• Events are almost always signaled by the occurrence of an interrupt or a trap.
• A trap (or an exception) is a software-generated interrupt caused either by an error (for example,
division by zero or invalid memory access) or by a specific request from a user program that an
operating-system service be performed.
1. Dual-Mode and Multimode Operation
• We need two separate modes of operation: user mode and kernel mode (also called supervisor
mode, system mode, or privileged mode). A bit, called the mode bit, is added to the hardware of the
computer to indicate the current mode: kernel (0) or user (1).
• With the mode bit, we can distinguish between a task that is executed on behalf of the operating
system and one that is executed on behalf of the user.
• When the computer system is executing on behalf of a user application, the system is in user mode.
However, when a user application requests a service from the operating system (via a system call),
the system must transition from user to kernel mode to fulfill the request.
2. Timer
• We must ensure that the operating system maintains control over the CPU.
3
