In computing, a clone is a hardware or software system that is designed to mimic another system. Compatibility with the original system is usually the explicit purpose of cloning hardware or low-level software such as operating systems. Application software can be cloned simply by providing similar functionality (all word processors have the same basic purpose), but may also be designed to support specific file formats (e.g. OpenOffice is intended to supplant Microsoft Office).
Clones are created for any number of reasons, including competition, standardization, and availability across platforms.
Hardware
When IBM came out with the IBM PC in 1981, other companies such as Compaq decided to put out a clone of the PC as a legal reimplemenatation from the PC's documentation or reverse engineering. As most of the components except the PC's BIOS were publicly available, all Compaq had to do was reverse engineer the BIOS. The result was a machine that had more bang for the buck than the archetypes that the machine resembled. The term "PC clone" fell out of use in the 1990s; the class of machines it now describes are simply called PCs or Intel machines (or even Wintel machines).
Software
Software can be cloned by reverse engineering or legal reimplementation from documentation or other sources, or by observing a program's appearance and behavior. The reasons for cloning may include circumventing undesirable licensing fees or acquiring knowledge about the features of the system. In the United States, the case of Lotus v. Borland allows programmers to clone the public functionality of a program without infringing its copyright.
