Operating System as a Resource Allocator: Why and How

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Questions and Answers

What is the primary role of an operating system from the computer's point of view?

To act as a resource allocator

What is the emphasis of a control program in an operating system?

To manage the execution of user programs and control I/O devices

According to Moore's Law, what prediction has held true about the number of transistors on an integrated circuit?

It would double every 18 months

What was the initial purpose of computing before it evolved into fixed-purpose systems?

To determine what could be done experimentally Signup and view all the answers

What aspect of computing led to a vast number and variety of operating systems?

Computers gaining in functionality and shrinking in size Signup and view all the answers

How does an operating system handle numerous and conflicting requests for resources?

By deciding how to allocate them to specific programs and users efficiently and fairly Signup and view all the answers

What are the three main objectives of an operating system?

Convenience, Efficiency, Ability to evolve Signup and view all the answers

Describe the responsibility of the operating system in managing computer resources.

The OS is responsible for managing the movement, storage, and processing of data. Signup and view all the answers

Explain the concept of device controllers in a computer system.

Device controllers are responsible for specific types of devices, maintaining local buffer storage and special-purpose registers. Signup and view all the answers

How does a common bus facilitate communication in a computer system?

A common bus provides access between components and shared memory. Signup and view all the answers

What is the significance of middleware frameworks in an operating system?

Middleware frameworks ease application development and provide additional features. Signup and view all the answers

Why is the ability to evolve an important objective for an operating system?

An OS should be constructed to permit effective development, testing, and introduction of new system functions without disrupting service. Signup and view all the answers

What is the role of a device controller in an operating system?

The device controller is responsible for moving data between peripheral devices and local buffer storage. Signup and view all the answers

Why does an operating system have a device driver for each device controller?

To provide a uniform interface to the device for the rest of the operating system. Signup and view all the answers

How does a memory controller ensure orderly access to shared memory?

By synchronizing access to the memory. Signup and view all the answers

What triggers the start of an I/O operation in an operating system?

The device driver loading the appropriate registers in the device controller. Signup and view all the answers

What notifies the device driver that a device controller has finished its operation in an operating system?

An interrupt. Signup and view all the answers

What information can a device driver return after an I/O operation in an operating system?

Status information like 'write completed successfully' or 'device busy'. Signup and view all the answers

What is an interrupt?

A signal sent by a hardware or device controller to the CPU, usually via the system bus, requesting for an I/O resource or indicating the completion of an execution. Signup and view all the answers

Where is the fixed location to which the CPU transfers execution when interrupted?

The starting address where the service routine for the interrupt is located. Signup and view all the answers

Why must interrupts be handled quickly?

Because they occur very frequently. Signup and view all the answers

How is the interrupt service routine executed?

The CPU stops the current computation, executes the routine, and then resumes the interrupted computation. Signup and view all the answers

Where is the table of pointers to interrupt routines typically stored?

In low memory, usually the first hundred locations. Signup and view all the answers

How is the interrupt service routine called indirectly through the table of pointers?

The interrupt vector, indexed by a unique number, provides the address of the interrupt service routine for the interrupting device. Signup and view all the answers

What is the purpose of saving the state information of whatever was interrupted in the interrupt architecture?

To restore this information after servicing the interrupt. Signup and view all the answers

Why must an interrupt routine explicitly save the current state before modifying the processor state?

To restore that state before returning. Signup and view all the answers

What happens after the interrupt is serviced in terms of the program counter and interrupted computation?

The saved return address is loaded into the program counter, and the interrupted computation resumes as though the interrupt had not occurred. Signup and view all the answers

How does the CPU hardware detect interrupt requests?

Through a wire called the interrupt-request line that the CPU senses after executing every instruction. Signup and view all the answers

What does the CPU do when it detects a signal on the interrupt-request line from a controller?

Reads the interrupt number and jumps to the interrupt-handler routine using that interrupt number as an index into the interrupt vector. Signup and view all the answers

What does the interrupt handler do after determining the cause of the interrupt?

Saves any state it will be changing during its operation, performs the necessary processing, performs a state restore, and executes a return from interrupt instruction. Signup and view all the answers

Study Notes

Operating System Overview

An operating system (OS) includes the kernel, middleware frameworks, and system programs that manage the system and ease application development.
The main objectives of an OS are convenience, efficiency, and the ability to evolve.

Computer-System Organization

A modern computer system consists of one or more CPUs, device controllers, and a common bus that provides access between components and shared memory.
Each device controller is responsible for a specific type of device and maintains local buffer storage and special-purpose registers.

Interrupts

An interrupt is a signal sent by a hardware or device controller to the CPU, requesting an I/O resource or indicating the completion of an execution.
The CPU stops what it is doing and immediately transfers execution to a fixed location when interrupted.
Interrupts are handled quickly, and a table of pointers to interrupt routines can be used to provide the necessary speed.

Interrupt Service Routine

The interrupt service routine executes, and on completion, the CPU resumes the interrupted computation.
The interrupt architecture must also save the state information of whatever was interrupted, so that it can restore this information after servicing the interrupt.

Role of Operating Systems

From the computer's point of view, the operating system is the program most intimately involved with the hardware.
An operating system acts as a resource allocator and a control program, managing the execution of user programs and controlling I/O devices.

Device Controller and Device Driver

The device controller is responsible for moving data between the peripheral devices it controls and its local buffer storage.
A device driver understands the device controller and provides the rest of the operating system with a uniform interface to the device.

Basic Operations of OS

Interrupts, storage structure, and I/O structure are key components of an operating system.
The CPU and device controllers can execute in parallel, competing for memory cycles, and a memory controller synchronizes access to the shared memory.

I/O Operations

To start an I/O operation, the device driver loads the appropriate registers in the device controller.
The device controller examines the contents of these registers to determine what action to take, and 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 that it has finished its operation via an interrupt.

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Description

Explore the role of operating systems in resource allocation from a system view perspective. Learn how operating systems manage hardware resources and allocate them to specific programs and users in the computer system.

Role of Operating Systems in Resource Allocation

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