Anthony J. Pennings, PhD


How IT Came to Rule the World, 2.6: The PC and the Floppy Disk

Posted on | September 21, 2010 | No Comments

The development of the floppy disk device was a crucial factor determining the success of the personal computer. Originally developed by David Noble at IBM in 1971 as a backup storage mechanism for their System/360’s magnetic core memories, the floppy disk was soon put to use for other purposes. An employee at IBM, Alan Shugart saw the implications of the new device for smaller computers. He realized that the floppy disk could provide a new storage device that was faster, had random access (meaning that one did not have to rewind an entire tape to find desired information) and could be portable. He started a company called Shugart Associates to build and market them. However, for the microcomputer to be effective it would need to combine the power of the microprocessor with the new storage mechanism. For a microcomputer to use the floppy disk, it required a new software package to run it, what IBM had already called a “Disk Operating System”. [1]

It was Gary Kildall who pioneered the first effective disk operating systems for microcomputers. Kildall earned his doctoral degree through the military’s ROTC program and so had a choice of going to Vietnam or teaching computer science at the Naval Postgraduate School in Monterey California. While teaching, he was also hired as a consultant by Intel to write software for its microprocessors, including a compiler later called PL/M. The compiler would allow programs written in languages like FORTRAN on larger computers to be used with the microprocessor. It was used on Intel’s Intellec-4 and Intellec-8, small computers that could lay some claim to the title of the first microcomputers, but were never marketed as such. Later, Kildall began emulating Intel’s new 8080 microprocessor on an IBM computer (Microsoft founders Gates and Allen would soon do something similar to write software for the Altair computer) and developed a new version of PL/M for it. He also decided at that time to write a program to control the mainframe’s disk drive. Using commands developed by DEC to access data from its DECtape, he began to write the code for the new operating system. DEC’s OS/8 and later its RT-11 had been important developments for PHP minicomputer series and showed that smaller computers could compete with the mainframes.[2] Pulling the pieces together, Kildall created his new operating system called CP/M, short for Control Program/Monitor.

Intel didn’t really want Kildall’s OS, but the software soon became the standard for a number of new microcomputers. CP/M was announced as a commercial product in April 1976. Kildall soon quit teaching to form a new company with his wife called Intergalactic Digital Research (later just called Digital Research) to market the operating system. CP/M was soon used by a number of small computers including the Osbourne, the first portable microcomputer, and the Kaypro which is shown below.

As C/PM became the standard for microcomputer operating systems, it inspired imitation. It was the foundation for another important operating system called Q-DOS (Quick and Dirty Operating System) that was bought by a small company called Microsoft as the basis for its own microcomputer operating system. MS-DOS became the software foundation of Microsoft’s empire and the successful early run of the IBM Personal Computer.[3]


[1] The beginnings of the floppy disk from Paul E. Ceruzzi’s A History of Modern Computing. Second Edition. Cambridge, MA: MIT Press. p. 236-237.
[2] Paul E. Ceruzzi’s A History of Modern Computing. Second Edition. Cambridge, MA: MIT Press was the source for Kildall’s development of CP/M from DEC sources. p. 238.
[3] Gary Kildall’s early story also from Robert X. Cringely’s Accidental Empires. New York: HarperBusiness, A division of HarperCollins Publishers. pp. 55-59.



AnthonybwAnthony J. Pennings, PhD is the Professor of Global Media at Hannam University in South Korea. Previously, he taught at St. Edwards University in Austin, Texas and was on the faculty of New York University from 2002-2012. He also taught at Victoria University in Wellington, New Zealand and was a Fellow at the East-West Center in Hawaii in the 1990s.


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