OS - System Operation | Operating Structure
** Operating Systems Tutorials **
This video tutorial on “System Operation” covers all the basics related to System Operation on computer systems. For any suggestions and doubts please do comments.
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This video is part of operating systems video course. Todays topic is System Operation.
Topics covered in this video are,
Dual Mode & Multimode Operation
Privileged Instructions
Timer
Modern operating systems are interrupt driven. If there are no processes to execute, no I/O devices to service, and no users to whom to respond, an operating system will ideal, waiting for something to happen.
Events are almost always signalled by 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.
An interrupt service routine is provided to deal with the interrupt.
Dual Mode & Multimode Operation
Modes of operation:
User Mode
Kernel Mode
Kernel mode is 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.
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.
Whenever a user application requests a service from the operating system (via a system call), the system must transition from user to kernel mode to fulfil the request.
Whenever the operating system gains control of the computer, it is in kernel mode.
privileged instructions
The dual mode of operation provides us with the means for protecting the operating system by using privileged instructions.
The hardware allows privileged instructions to be executed only in kernel mode. If an attempt is made to execute a privileged instruction in user mode, the hardware does not execute the instruction but rather treats it as illegal and traps it to the operating system.
Ex of privileged instruction: System call, I/O Control, timer management.
Timer
We must ensure that the operating system maintains control over the CPU. We cannot allow a user program to get stuck in an infinite loop or to fail to call system services and never return control to the operating system. To accomplish this goal, we can use a timer.
A timer can be set to interrupt the computer after a specified period. The period may be fixed or variable.
A variable timer is generally implemented by a fixed-rate clock and a counter.
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About the Course
Operating systems are an essential part of any computer system. Similarly, a course on operating systems is an essential part of any computer science education. This field is undergoing rapid change, as computers are now prevalent in virtually every arena of day-to-day life — from embedded devices in automobiles through the most sophisticated planning tools for governments and multinational firms. Yet the fundamental concepts remain fairly clear, and it is on these that we base this video course. This is an introductory course in operating systems at the junior or senior undergraduate level or at the first-year graduate level. It provides a clear description of the concepts that underlie operating systems. As prerequisites, we assume that the reader is familiar with basic data structures, computer organisation, and a high-level language, such as C or Java.
For more information, Please write back to us at samirshahtutorials@gmail.com or call us at IND: +91 9558840366
