In the beginning, the hardware vendor owned it all (a single vendor provided all equipment and all software). Not long after mainframes came into general use in enterprises, portability became recognized as an important goal. As faster computers became available, customers wanted to upgrade. They were stymied because the newer machines were incompatible. Workarounds were developed. For example, IBM pioneered the use of microcode on its System/360 models to enable them to run 1401 applications.
Such emulators were often used to allow so-called legacy applications to run (albeit with significant overhead) on newer machines. According to a comment by Tom Bell on one blog, Good Morning Silicon Valley, programs written for the IBM 1401 (announced October 5, 1959 and withdrawn February 8, 1971) continued to function well into the 1990s.
The virtue of portability, always important, became obvious to everyone once the IBM PC (Model 5150) entered the marketplace on August 12, 1981. With its open architecture, it and its successors were an instant and enduring hit, with one billion shipped by the end of 2008, and 135 million during the first half of 2010, according to Worldometers, which tracks computer shipments in real time. Brandon eBlanc of Microsoft says that 150 million licenses for Windows 7 were sold between November 2009 and June 2010. Cheap multisourced components, the related DOS operating system, and frequent improvements in processors and other components that still retained op-code-level compatibility sparked the personal computer revolution.
In September 1991, Linus Torvalds released Linux version .01, and it became open source under the GNU Public License (GPL) in February 1992. Linux jumpstarted the open source revolution. Open source versions of Linux and all of the Internet-oriented software built on top of it, such as Apache (see below), MySQL, and PHP/PERL/Python (collectively the LAMP architecture) and the myriad of ISPs offering hosting services built on that architecture amply demonstrate the benefits of openness.
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