Bill Mensch

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Bill Mensch
Bill Mensch - Western Design Center (12924524534).jpg
William D. Mensch, Jr., 2014
Born (1945-02-09) February 9, 1945 (age 75)
NationalityUnited States
EducationB.S. - University of Arizona
A.S. - Temple University
OccupationMicroprocessor designer

William (Bill) David Mensch, Jr. (born February 9, 1945), is an American electrical engineer born in Quakertown, Pennsylvania. He was a major contributor to the design of the Motorola 6800 8-bit microprocessor, was part of the small team led by Chuck Peddle that created the MOS Technology 6502, and he designed the 16-bit successor to the 6502, the 65816.

Mensch is the founder, chairman, and CEO of the Western Design Center (WDC) located in Mesa, Arizona. Prior to founding the Western Design Center in 1978, Mensch held design engineering and management positions at Philco-Ford, Motorola, MOS Technology and Integrated Circuit Engineering.[1] At WDC, Bill Mensch worked primarily on extending and expanding the 6502 architecture. His designs are widely used in embedded systems and implantable, electronic, life-support devices.

Education, teaching, honors[edit]

Mensch graduated with an associate degree from Temple University in 1966 where he was a member of Sigma Pi fraternity.[2] He received his bachelor's degree in electrical engineering from the University of Arizona in Tucson in 1971. He has taught classes at Arizona State University, including courses on system-on-a-chip (SoC) IC design. Mensch is a Senior Member of the IEEE. In 2004 he was inducted in the Computer Hall of Fame (hosted by the San Diego Computer Museum, part of the San Diego State University Library), and in 2005 was presented with a Lifetime Achievement Award from the University of Arizona's College of Engineering.[1]

Engineering achievements[edit]

Based on his participation in the basic circuit design, definition, and system design of the Motorola 6800 microprocessor and supporting computer chips, Mensch is a co-holder of several 6800 family patents, including the 6800 CPU, 6820/21 PIA, 6850 ACIA, and 6860 modem chip. He was the sole integrated circuit (IC) design engineer of the 6820/21 PIA, which was the first peripheral IC to have bit-programmable I/O.[1]

Along with three other engineers at MOS Technology, Mensch holds the patent on the decimal correct circuitry in the 6502 CPU. He was responsible for the basic circuit design, transistor sizing, instruction decode logic (wishing to minimize the number of levels of logic so as to achieve higher speed operation), oscillator design and buffer design. Prior to leaving MOS Technology in 1977, Bill Mensch became the microprocessor design manager at the company.

Western Design Center[edit]

Shortly after founding the Western Design Center (WDC) in 1978, Commodore contracted WDC to develop what they called a "macro-micro", a macro-programmed CMOS processor that could be used in a small and powerful calculator. However, WDC was not able to complete the project, and Commodore ended their relationship with the new company.[3]

The first major effort of Mensch and his team was the development of the WDC 65C02, an enhanced version of the NMOS 6502 microprocessor. The 65C02, in addition to being implemented in CMOS circuit technology that reduced power consumption and improved noise immunity, added some new instructions and corrected a number of defects that were present in the NMOS 6502. The 65C02 was subsequently adopted for use in the Apple IIc computer and, later, in an enhanced version of the Apple IIe.

Mensch's next design, which was to become an important product at WDC, was a 65C02-compatible 16-bit microprocessor, the 65C816 (now designated the W65C816S). The 65C816's design came about following consultation with Apple and was adopted by them for use in the Apple IIGS computer. The 65C816 was later chosen as the core of the processing unit that powered the popular Super Nintendo Entertainment System.

Mensch developed the Mensch Computer as a means to promote the W65C816S microprocessor. It was a computer system designed around the WDC W65C265S microcontroller, which contains a W65C816S core. The Mensch Computer, which includes the Mensch Works software suite, was produced for a time by WDC and was geared toward hobbyist and educational applications.

As of 2012, Bill Mensch was still involved with design engineering at WDC, in addition to his work as CEO. He has written the upcoming Terbium processor family's data sheets and will be making the major RTL design decisions associated with that processor architecture.

Chuck Peddle and Bill Mensch are regarded as personal computer pioneers, because both the 6502 technology and business model were instrumental in helping launch the personal computer revolution.[4][5]


Bill Mensch has four children and resides with his wife, Dianne, in Superstition Mountain, Arizona.[1]

Mentions in press and literature[edit]


  • "What's the Proper Goal for an IP Business Model". Silicon Strategies editorial.
  • "The Chips We Live by". Forbes magazine cover story, Michael S. Malone, January 6, 1998. (Online version)
  • "A Business Model? for IP Providers". FSA Forum/Fabless Forum (member publication of the Fabless Semiconductor Association).


  • Bagnall, Brian (2019). Commodore: the final years. Variant Press. ISBN 978-099403103-7.
  • Bagnall, Brian (2006). On The Edge: The Spectacular Rise and Fall of Commodore. Variant Press. ISBN 0-9738649-0-7.
  • Drescher, Nancy (1997). Which Business?: Help in Selecting Your New Venture. Psi Successful Business Library. Bookworld Services. 358 pp. ISBN 1-55571-390-4.
  • Gilder, George (1989). Microcosm: The Quantum Revolution in Economics and Technology. New York, NY: Simon & Schuster. ISBN 0-671-50969-1. Touchstone/Free Press reprint ed., 1990: ISBN 0-671-70592-X.


  1. ^ a b c d "WDC Founder". Mesa, Arizona: The Western Design Center, Inc. 2012. Archived from the original on May 8, 2013. Retrieved 2013-03-09.
  2. ^ "Notable Alumni". Sigma Pi Fraternity, International.
  3. ^ Peddle, Chuck (June 12, 2014). "Oral History of Chuck Peddle" (Interview). Interviewed by Doug Fairbairn and Stephen Diamond. 1:53:00.CS1 maint: location (link)
  4. ^ "Microchips That Shook the World". IEEE Spectrum.
  5. ^ "Digging Into The 6502". Apple II history.

External links[edit]

Media related to Bill Mensch at Wikimedia Commons