Operating Systems (Types)
An operating system is a specialized software package that operates something on behalf of someone. The object it operates is clearly the computer itself--the operating system operates the computer. The entity it operates on behalf of is a human user, or a community of human users. Functions of an operating system include providing a uniform interface across differing hardware, providing abstractions such as files, windows, clocks, etc., that humans prefer, and providing mechanisms for enforcing security policies. Every general-purpose computer requires some type of operating system that tells the computer how to operate and how to utilize software applications and hardware that are installed. This frees the user from the tedium of having to worry about the minute details of file reads, writes, scheduling of process threads, and the like.
Operating systems can be classified in various ways, depending for example on whether they allow only a single user or more than one user at a time; or depending on whether they allow one thread or many; or depending on whether they allow multiprocessing (the use of more than one processor) or multitasking (the running of more than one task on a processor).
The earliest operating systems were rudimentary and only allowed for text input. This kind of operating system is now said to be text-based, or to have a text shell. Examples of this kind include MS-DOS (the precursor to Microsoft Windows), and Unix, which was first released in 1969 from Bell Labs. It became obvious, after a time, that a mere text interface was not adequate, and efforts began to be made to develop a Graphical User Interface (GUI) which would allow for graphics, icons, drag-and-drop, and so on. The first successful GUI for personal computing devices was the system used on the Apple Macintosh, which grew partly from research done at Xerox's Palo Alto Research Center (Xerox PARC). GUI interfaces were also developed for Unix (X-Windows), and for MS-DOS (Windows 3.1). The Macintosh system was a real operating system with a GUI interface, rather than being a GUI interface running on top of a text shell. However, early X-Windows and Microsoft Windows 3.1 were both GUIs running on text shells, where mouse movements and operations on icons, etc., would be translated into text commands and executed by the underlying shell operating system that was hidden from the user. Later, with the coming of Windows 95, this shortcoming was fixed.
Early operating systems did not allow for multiprocessing or multitasking, but nearly every one of recent date does, for obvious reasons, as computers and software have continued to increase in complexity and user demands continue to increase likewise.
In the 1960s, there was a project called MULTICS, which aimed to create a "computing utility." This was back in the day when computers were owned soley by corporate owners and were housed in separate large rooms and were expensive to purchase and operate. Few envisioned that it would ever be possible for individuals and families to purchase and use their own computers, and the idea of MULTICS was to form a computing utility that would enable people to purchase computing services, much as they might purchase electricity, water, or heating gas for home use. After several years and much money spent, MULTICS failed and the sponsors withdrew. A few of the researchers who had worked on MULTICS decided to work on a more modest effort that nonetheless preserved some of the worthwhile aims of the failed grand effort, and Unix was born. (The name "Unix" is merely a pun on MULTICS, and does not stand for anything.)
Unix is, and has always been, a multi-user operating system. In fact, it is partly for this reason that Unix continues to be a popular choice for college and university computing networks with hundreds or thousands of users. By contrast, many other operating systems, including Windows 95 and the MacOS versions, are meant for a single user at a time. Microsoft has its own Windows variant called Windows NT which is supposed to be a competitor to Unix in the multi-user area, but it has not succeeded in dislodging Unix as the predominant choice. One of the important concerns in a multi-user system is obviously security--it is important for multiple independent users to be able to use the system in a meaningful way without being able to intrude upon each other, and without having to fear loss of privacy. On Unix, this is done by providing a method for file security, and a way to create individual accounts that are protected by passwords. These features are missing on most operating systems for personal computers, but Linux, a freeware Unix variant developed in the 1990s, has them.
Unix is also preferred for scientific computing where robustness, i.e., the lack of operating system crashes, is an issue. In personal computing where the applications used might be just for personal use or amusement, such as for electronic mail, Internet access, word processing, and the like, robustness is not as serious an issue since most people don't use a computer continuously for very many hours at once. However, anyone who has used Windows or other PC operating system has experienced crash failures (in fact, Windows 98, the successor to Windows 95, crashed during its demonstration to the world by Bill Gates, chairman of Microsoft). In technical terms, it would be said that the "mean time between failures" of an OS such as Windows is rather small perhaps just a day or less. This may just cause a little irritation to a lay user, but is a very serious matter in scientific computing, where for instance a simulation or a long-running program may have to be run continuously for weeks or months. Such a program obviously has no chance of being run to completion on Windows 95, and needs to be on Unix, which is a stable operating system that can go years without crashing.
On the other hand, it is true that Unix is a less user-friendly operating system than modern Windows and other releases. This is largely because it was originally conceived in a different era, and still retains some of the distinctive features of its humble beginnings. Lay users who have little training or interest in a deep study of computers and are thus keen to use them with minimal training, often find it easier to use Windows, which is thus the predominant operating system in the personal computing market.
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