Suppose you're back in the late 1970, before off-the-shelf computer programs have really been invented. You want to program your computer to work as a word processor so you can bash out your first novel—which is relatively easy but will take you a few days of work. A few weeks later, you tire of writing things and decide to reprogram your machine so it'll play chess. Later still, you decide to program it to store your photo collection. Every one of these programs does different things, but they also do quite a lot of similar things too. For example, they all need to be able to read the keys pressed down on the keyboard, store things in memory and retrieve them, and display characters (or pictures) on the screen. If you were writing lots of different programs, you'd find yourself writing the same bits of programming to do these same basic operations every time. That's a bit of a programming chore, so why not simply collect together all the bits of program that do these basic functions and reuse them each time.
A typical computer architecture linking the hardware to the applications via the BIOS and the operating system.
That's the basic idea behind an operating system: it's the core software in a computer that (essentially) controls the basic chores of input, output, storage, and processing. You can think of an operating system as the "foundations" of the software in a computer that other programs (called applications) are built on top of. So a word processor and a chess game are two different applications that both rely on the operating system to carry out their basic input, output, and so on. The operating system relies on an even more fundamental piece of programming called the BIOS (Basic Input Output System), which is the link between the operating system software and the hardware. Unlike the operating system, which is the same from one computer to another, the BIOS does vary from machine to machine according to the precise hardware configuration and is usually written by the hardware manufacturer. The BIOS is not, strictly speaking, software: it's a program semi-permanently stored into one of the computer's main chips, so it's known as firmware, it is usually designed so it can be updated occasionally, however.
Photo: Typical computer architecture: You can think of a computer as a series of layers, with the hardware at the bottom, the BIOS connecting the hardware to the operating system, and the applications you actually use (such as word processors, Web browsers, and so on) running on top of that. Each of these layers is relatively independent so, for example, the same Windows operating system might run on laptops running a different BIOS, while a computer running Windows (or another operating system) can run any number of different applications.
Operating systems have another big benefit. Back in the 1970 and early 1980 virtually all computers were maddeningly different. They all ran in their own, idiosyncratic ways with fairly unique hardware (different processor chips, memory addresses, screen sizes and all the rest). Programs written for one machine (such as an Apple) usually wouldn't run on any other machine (such as an IBM) without quite extensive conversion. That was a big problem for programmers because it meant they had to rewrite all their programs each time they wanted to run them on different machines. How did operating systems help? If you have a standard operating system and you tweak it so it will work on any machine, all you have to do is write applications that work on the operating system. Then any application will work on any machine. The operating system that definitively made this breakthrough was, of course, Microsoft Windows, written by Bill Gates. It's important to note that there were earlier operating systems too. You can read more of that story in our article on the history of computers.
0 comments:
Post a Comment