The operating system for IBM-compatible computers was first called MS-DOS. Although at times you may think that the "MS" stands for "malicious system," it really stands for Microsoft, the company that wrote the program.
Computers whose disk drives, memory, etc. have different operating characteristics from IBM-compatible PCs, such as the Apple Macintosh, use different disk operating systems. Although all computers, even room-sized mainframes, must use a disk operating system, the term "DOS" has come to be associated with IBM-compatibles.
The more generic term is now simply "OS" (pronounced as separate letters) for operating system, dropping out the word "disk." Any operating system must be copied or "loaded" into a computer’s memory from a disk, either internal or external, before the computer can be used. This is called "booting" the computer.
Once the computer is initialized by loading the basic instructions supplied by the OS, it is ready to run your application software, such a word processing or personal finance program, or a game for you or your kids.
The current combination of DOS and Windows, which is the core operating system and an environment making it easier to use, is in the process of being replaced by an all-in-one operating system and friendly user environment called Windows 95.
The Apple Macintosh operating system, currently called System 7.5, has recently received a new name -- Mac OS. The reason is that Apple has finally authorized other companies to make clones of the Mac in order to broaden the base of installed machines, thereby increasing market share for their system and allowing more software to be sold by Apple and others.
Apple’s marketing people feel the operating system needs an official name, one the clone makers can use in their advertising to show that any software written for the genuine Apple Macintosh will also work on their machines.
Other popular operating systems for use on personal computers and workstations, which are like PCs on steroids (more powerful processors, tons of chip memory, huge hard disks) are OS/2, Windows NT, UNIX, Solaris, NeXTStep, Linux, and many others.
All require different amounts of hardware horsepower, work with different microprocessors, have varying amounts of commercial software available for them, and are used for specialized applications such as engineering, scientific, graphics and publishing, financial, and manufacturing.
Minicomputers and mainframes use dozens of operating systems, some dating back decades.
Most of the more esoteric and powerful operating systems require custom-written software, which large corporations are more likely to use.
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