What is an OS?

An intermediary layer between user and computer hardware Provides abstraction for user to communicate with hardware Serves as a Resource Allocator

Resources can be shareable and non-shareable IO Devices, timers, disks, memories, network interfaces, printers etc.

top-down view is that it is a program that acts as an intermediary between a user of a computer and the computer hardware, and makes the computer system convenient to use

the bottom-up view is that operating system is a resource manager who manages the hardware and software resources in the computer system

Purpose

• Solve User Problems
• Efficiency for User
• Connivence for User

Terms / Components

Kernel

Those files / software which are stored in the RAM from ROM to load the operating system into the memory

there are four events that cause execution of a piece of code in the kernel. These events are: interrupt, trap, system call, and signal.

Entry points into the operating system kernel
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Bootstrap Loading

The process of loading the OS into the RAM

Resource Multiplexing

1. In Time
2. In Space

Process

A process may require the combination of CPU utilisation and IO utilisation CPU manges computation and IO devices Therefore, a process needs to tend to CPU for computation as well as IO devices A process may consist of many threads

Frequency

A frequency of 2.3 GHz can about perform 2.3 Giga Oscillations

See Also : Timeline of the Computer Systems