Brief review of operating systems

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Early computers lacked operating systems (see History of operating systems). A human operator would manually load and run programs. When programs were developed to load and run other programs, it was natural to draw their name from the human job they replaced.

Today, the term is most often used colloquially to mean all the software which "comes with" a computer system before any applications are installed.

The operating system ensures that other applications are able to use memory, input and output devices and have access to the file system. If multiple applications are running, the operating system schedules these such that all processes have sufficient processor time where possible and do not interfere with each other.

In general, the operating system is the first layer of software loaded into computer memory when it starts up. As the first software layer, all other software that gets loaded after it depends on this software to provide them with various common core services. These common core services include, but are not limited to: disk access, memory management, task scheduling, and user interfacing. Since these basic common services are assumed to be provided by the OS, there is no need to re-implement those same functions over and over again in every other piece of software that you may use. The portion of code that performs these core services is called the "kernel" of the operating system. Operating system kernels had been evolved from libraries that provided the core services into unending programs that control system resources because of the early needs of accounting for computer usage and then protecting those records.

It is also noteworthy that some people use "kernel" to mean the core piece of the OS that deals most directly with the hardware, and have a slightly broader definition of "operating system". They would define "operating system" to refer to the kernel plus some of the basic computer programs and libraries that are necessary to use the kernel. An interesting essay about the difference between the kernel and the operating system, from the perspective of a broader definition of OS, can be found here: Linux and GNU (http://www.gnu.org/philosophy/linux-gnu-freedom.html). It should be stressed that neither definition is completely accepted among the computer science community.

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A basic review of operating systems