Operating System Concept Free Download Books

Introduction

Modern general-purpose computers, including personal computers and mainframes, have an

operating system to run other programs, such as application software. Examples of operating

systems for personal computers include Microsoft Windows, Mac OS (and Darwin), Unix, and

Linux.

The lowest level of any operating system is its kernel. This is the first layer of software

loaded into memory when a system boots or starts up. The kernel provides access to various

common core services to all other system and application programs. These services include, but are

not limited to: disk access, memory management, task scheduling, and access to other hardware

devices.

As well as the kernel, an operating system is often distributed with tools for programs to

display and manage a graphical user interface (although Windows and the Macintosh have these

tools built into the operating system), as well as utility programs for tasks such as managing files

and configuring the operating system. They are also often distributed with application software that

does not relate directly to the operating system's core function, but which the operating system

distributor finds advantageous to supply with the operating system.

The delineation between the operating system and application software is not precise, and is

occasionally subject to controversy. From commercial or legal points of view, the delineation can

depend on the contexts of the interests involved. For example, one of the key questions in the

United States v. Microsoft antitrust trial was whether Microsoft's web browser was part of its

operating system, or whether it was a separable piece of application software.

Like the term "operating system" itself, the question of what exactly should form the

"kernel" is subject to some controversy, with debates over whether things like file systems should

be included in the kernel. Various camps advocate microkernels, monolithic kernels, and so on.

Operating systems are used on most, but not all, computer systems. The simplest computers,

including the smallest embedded systems and many of the first computers did not have operating

systems. Instead, they relied on the application programs to manage the minimal hardware

themselves, perhaps with the aid of libraries developed for the purpose. Commercially-supplied

operating systems are present on virtually all modern devices described as computers, from personal

computers to mainframes, as well as mobile computers such as PDAs and mobile phones.