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    Cmmodore pioneered and popularized so much of the technology we use today.  Commodore Business Machines was a juggernaut in the late 1970's and early 1980's.  Commodore history is rich with interesting stories and fascinating facts.  
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The Rise of MOS Technology & The 6502
Written by Ian Matthews of commodore.ca February 15, 2003
Seriously revised and expanded on January 18, 2006, Last update June 26, 2006
Last minor update: June 4, 2007

MOS Technogloy, Inc Valley Forge Corporate Center, Norristown PA, CSG Logo GraphicAt the heart of what people think of as Commodore, was a company called MOS Technology.  MOS' claim to fame was their development and manufacturing of the wildly successful 6500 line of microprocessors which in addition to being used in nearly all Commodore computers and floppy drives, was also the driving force of all pre-1984 Apples.  However, MOS was not started by Commodore or even by the Engineers who made it famous, like Chuck Peddle and Bill Mensch.

Vintage Commodore Calculator with red LED's.  796MAllen-Bradly Logostarted MOS as a second source for Texas Instruments (TI) chips and even produced the famous Atari PONG chip for limited time.  A major player in the calculator business called Commodore Business Machines quickly became  MOS' number one customer in the early 1970's. 

During our January 2006 interview with Chuck Peddle, we were informed commodore.ca that MOS was always pronounced M.O.S. so as not to confuse it with the MOSTek which was a competing company that was also established in 1969. 

Motorola's Refusal to Innovate
As one of the lead Motorola 6800 engineers at a time in before most people had even heard the term "CPU", Chuck Peddle was often tasked with explaining the capabilities of a microprocessor to large industrial Motorola 6800 CPU - Possibly the Worlds First Processormanufactures, like Ford.  After an education cycle, the Engineers were usually highly impressed with the potential for such a device but at US$300 ($1200 in 2005 dollars!) would inevitably say it was far to expensive to use.  Chuck asked Motorola's customers the price they thought it would be possible to put CPU's into their mass market products.  $25 came up as the magic number. 

As one might guess, Engineers discussing a $25 version of a successful $300 product, did not impress Motorola management.  Conversely, Management's failure to pursue obvious improvements to their chip did not impress Motorola's engineers. When Chuck received a formal letter from management telling him to stop working on a cost reduced version 6800, he saw an opportunity. 

Chuck Peddle and Bill Mensch took six other key Motorola 6800 engineers to work for an old General Electric colleague who ran a small "fab" called MOS Technologies.  Bill MOS Technology 6502 Team Picture in Electronic Times 1975 including Bill Mensch and Chuck PeddleMensch explained that Chuck handled most of the negotiation with MOS and that part of the deal was that each of the eight were to receive "a fraction of the profits."  The key word here is 'profits'.  At this time, not many companies actually made money from chips and as your might expect, Bill explained that when the group found out about the deal months later "they were all pissed!"  To the right is a fantastic 1975 picture and article, taken from Bill Mensch's personal collection of the design team.

As might happen today in your work environment, it irked the existing MOS staff to have an entire team of highly qualified and recognized people parachuted into the organization.  Bill says that "it was painful, I had two flat tires in my first week at MOS."   An MOS staffer of Italian decent told him "you don't mess with the Godfather", referring to one of the MOS Vice Presidents who was unhappy with the recent conversion of Motorola staff.  The existing staff wanted to work on development of a microprocessor and correctly felt they would be largely left out of the process.

Chuck said he gave the engineers a "..tight list..." of features to build into the chip along with a fixed die size.  To get to the $25 price they need to produce only the instructions that its customers would required, nothing extra. 

MOS 6500
The Inventor of the Personal Computer and the 6502 Processor, Chuck Peddle PhotoWithin a year the team developed the CPUs line that would change the world; The MOS 6500 series.  There are many interesting stories surrounding the 6501 but the most amazing is that Bill Mensch was able to take the 6501 schematics, create a layout completely by hand (remember no-one had computers back then) and produce a working CPU on the very first attempt.  This was unheard of.  Several engineers we talked with have said that they had never seen anyone manually produce a successful chip on the first pass.  It often takes 10 or more tries to get it right.  In a January 2006 interview with www.commodore.ca , Chuck said "Bill ...was like a layout savant... he can just picture an entire layout in his head."

The Fabled MOS 6501 CPUNote that the MOS 6501 shown to the right is extremely rare and was purchased directly from the Norristown, PA factory for the princely sum of $20.  When we asked Chuck about it in March 2007, he said "...we stopped producing the 6501 so none really made it to market in any numbers.  We never intended anyone to buy it anyhow.  It was an in your face to Motorola...  It is indeed rare."

The 6501 and 6502 where nearly identical.  The primary difference was the pin arrangement; a 6501 is pin compatible with the  Motorola 6800 and 6502 is not. 

The group was not without humour.  One of the important designers on this chip was Rod Orgill (who can be seen in this picture).  Bill said that one of the 6502 pins is officially named SO (Set Overflow).  "Chuck, Rod, and I know that it's real name is Sam Orgill... Rods dog".

AMD Technicial holding a CPU Wafer in 2004In the 1970's, 70% of the industries chip production were defective and therefore garbage.  This substantially increased the cost of each viable chip.  When a chip is being laid out for etching on a silicon wafer, it drawn at a large scale and then photo reduced over an over again (just like a photocopy reduction) until its microscopic size will fit on the required die.  Each reduction layer is called a Mask.  MOS figured out a process to repair Masks as they are reduced.  The end result was that they had a 70% success rate.  This obviously reduced the per chip cost of manufacturing and made the $25 processor a possibility.

Chuck explained that selling a dramatically less expensive CPU was not as easy as it sounded.  A few years earlier there had been a high profile scam involving a company that claimed it could produce mainframe terminals it would lease for just $10 per month.   The company went bankrupt in a cloud of scandal after taking millions of dollars from investors, and blamed the failure on industries inability to produce cheap chips. 

In an effort to drum up interest in the chip they ran an advertisement stating that anyone could see and buy the amazing $25 microprocessor at WestCon (Western Electronics Show and Convention) in 1975.  Unfortunately, when MOS arrived at the show they were told that, in an effort the keep the show 'high brow', exhibitors were not allowed to sell product at their booths.  Chuck quickly rented a nearby hotel room and had is very attractive wife, sit at a table with two full glass jars of 6501's and 6502's.  Little did most people know that all of the chips in the bottom of those jars were defective.  Image is everything. 

Motorola's Anger: A Blessing In Disguise
In June of 1975, soon after the show, Motorola realized they had turned their engineers into their competition.   Motorola got mad and sued MOS for infringement of 6800 patents.  Chuck said "...there was no substance to their claims..." but it scared the old line industry management at Allen-Bradley.  "As soon as lawyers got involved, they wanted out." said Chuck.  As a shock to everyone, Allen-Bradley walked away from MOS and basically gave it to the existing MOS management team. 

It is interesting to note that Bill Mensch tells a more complete version of this important part of the story.  "It was not about patent infringement; it was about intellectual property."  Those eight engineers knew an awful lot of unpatented concepts developed at Motorola and that is what Motorola was trying to protect.  "We knew we were (infringing).  The (MOS) 6520 was a direct copy of the (Motorola) 6820."  MOS had agreements in place with Motorola and "...We paid Motorola all along."

A Star is Born: The 6502
A Blue KIM1 Kim-1Commodore CSG MOS 6502 Processor Used in Everything from ALL early Apples to Nearly All Commodore ProductsMOS designed and manufactured two 6502 trainers call the TIM1 (Terminal Input Monitor) and KIM-1 (Keyboard Input Monitor).   They are often incorrectly referred to as kit computers, like the Altair.  The TIM and the KIM came fully assembled and were the world's first single board computers.

Like many great products, the 6502 had a humble beginning.  Bill told us that he and a few others wrote a nearly complete specification for the 6500 line "...on the back of an Arby's napkin!"  When it was completed in the Spring of 1975, the MOS 6502 initially ran at about 1Mhz, the same as the Motorola 6800.  However, 6500's performed about 4 times the number of calculations a 6800 could. 

1976 Advert Buy a MOS KIM-1 for $245 In a 2005 book about Commodore, Bill Mensch is quoted as saying he had the 6502 running at about 12Mhz.  Remember that it wasn't until 1983 that Motorola released the 68010 and Intel took until 1984 to release a 10Mhz 80286 chip.  This was WAY ahead of its time.   In our discussions, Bill clarified this amazing story, by explaining that the chips he had running over 10Mhz were actually early manufacturing errors to be discarded as trash.  For the fun of it, he played with these flawed units just to see if he could get them to work.  When I asked him why he did not present these as notable engineering successes to industry or to the Guinness Book of Records, he said "I was worried about eating... not making records."

Motorola may or may not have had a solid legal case but they definitely had something that MOS did not, money.  It did not take long for MOS to kill the 6501.  The suite dragged on a for a few years and MOS eventually settled the claims with a $200,000 payment to Motorola.

The Calculator Wars
In 1975, Commodore had a huge inventory of Texas Instruments based calculators when the market began to collapse.  Because Commodore sourced their TI chips from MOS, MOS was in financial trouble. Then the unthinkable happened.  Texas Instruments started retailing their own brand of calculators at a prices less than Commodore manufacturing cost.  The November 1975 New Scientist magazine reported "Commodore is struggling to survive. Two weeks ago the firm reported its end of year results, which showed a $4.3 million loss on sales which were up 12 per cent over the year to $55.9 million."  

MOS Technology / CSG / Commodore Semiconductor Group building signCommodore's founder and CEO, Jack Tramiel, convinced Commodore's Canadian financier, Irving Gould, that vertical integration (owning all of the parts of production) was the only way Commodore could survive.  Soon after, the September 1976 edition of New Scientist noted "Commodore, quoted at $60 million on the New York Stock Exchange, has acquired 100 per cent of the equity of MOS Technology Inc of Pennsylvania in exchange for a 9-4 per cent equity stake in Commodore. MOS Technology is privately owned and valued at around $12 million."

Commodore continued the KIM-1 and Jack Tramiel personally approved the development and production of Chuck Peddles unified computer, the PET.

In an effort to start sales of the 6502, MOS staff ran a quick tour of the US, dropping into see major manufacturing companies like Ford.  On the trip Chuck was told that two young guys working in their garage wanted some help using the 6502.  Steve Jobs and Steve Wozniak were working on the first Apple and Chuck was happy to lend a hand even though he did not design the 6500 line for computer use.  "...Not in a million years... it was supposed to go into industrial and consumer products."  Little did Chuck know that the computer business would quickly become the mass market consumer product he was targeting.

Commodore PET 2001 ChickletOver the previous few years Chuck had met with hundreds of computer enthusiasts, educational institutions and main frame corporate users.  He learned that "...what people wanted was a computer that looked like a terminal."  He bought a little book on how to build your own television, written by the legendary Adam Osborne and contracted out the construction of a wood case to house the computer.  (Yes; that's right, the prototype was made of WOOD!).  Using a motherboard based on the 6502 processor Chuck designed and built the worlds first computer which would later be named the Commodore PET.  Explaining how experimental this was, Chuck said "The first time we turned it on, the image was upside down... we got Adam's book out to figure out how to turn it..."

In a January 2006 interview, Chuck told a great story about trying to sell the CPU's to Atari.  Atari was so worried about industrial espionage that they sequestered their top engineers in a remote facility on a dirt road, several hours from Los Angeles.  Chuck packed he and his wife for brief holiday and made plans to stop in to see this top secret Atari think tank on the way.  Atari was working on three new options for their new machine one of which called for a 6502, an IO chip and a custom chip.  Atari wanted him to produce the 6502 and the IO chip for just $12!  By this time, Chuck estimated that MOS' production cost on two of those chips was just $4 and so it was easy to agree; the Atari 400 and 800 were announced in December of 1978.

Engineer Exodus & The Rise of 16Bit
WDC's Bill Mench PhotoShortly before the Commodore take over, frustrated 6502 co-designer Bill Mensch left the company.   It had been made clear that "Commodore was going into Game Systems... stopping microprocessor development"  I was the head of Microprocessor development... (and) I saw the writing on the wall". 

WDC_w65c816s8pl.jpg (14048 bytes)There was a desire among MOS engineers to design a 16 bit version of the 6502 but Commodore's management was apathetic and would not fund the project.  In the end Commodore never produced a 16 bit 6500 but Bill Mensch Western Design Center Logowho still retains ownership of the WDC, did.  The 65C816 is now in over 5 Billion (yes, that's Billion with a "B") devices.  That chip can run in both 8 and 16 bit modes (hence the 816 designation).  From pacemakers in your chest, to dashboard controllers in your car, to the famous Super-Nintendo, Bill's low voltage, highly tested 6500 version is ubiquitous. 

acorn_6502.jpg (203660 bytes)The original 8 bit 6502 and many MOS derivatives are legendary.  It was put into everything from the Apple I and II, to the VIC and C64, to the original Nintendo Game System.  The 6502 was also used in many of the original arcade video games like Defender, Battlezone, and Asteroids. Bill Mensch's Western Design Center holds most of the 6500 related patents and still are responsible for their production.

Commodore's CEO, Jack Tramiel started to "play" with the lives of some of the MOS key staff shortly after the take over and many of the key players left the company.  Most notably, Chuck Peddle left and took the equivalent to the Chief Technology Officer position with Apple, before returning to MOS a few months later. 

Commodore set up the Moore Park Research Center in California for Chuck and other important West Coast based engineers.  Just a few years later, in a moment of anger, Jack ordered it closed.  Most of the MOS Engineers, including Chuck Peddle, refused to move to Commodore's Pennsylvania headquarters.  By the mid 1980's Commodore had only about a dozen certified Engineers working for them world wide, most of them at MOS.

CSG 6510 - no MOS logoThe Slow Decay of the 80's
Even though it had renamed the company "Commodore Semiconductor Group" (CSG) shortly after the acquisition, all MOS production used the old MOS logo until 1989.

Using MOS' Engineers and facilities, Commodore was able to produce prototype chips in days rather than months and at practically no cost.  Other companies, like Atari, Apple, and Osborne would have to spend tens of thousands of dollars and wait weeks or months for new chips.  MOS was critical to Commodore's fast paced style of business in the 1970's and early 80's.  Commodore Engineers could get a chip produced without so much as formal paperwork.  When Bill Herd (the Plus/4 and C128 Engineer) quit and went to work for a chip small design shop, he was shocked that he could not simply order up new prototype chips. 

Amiga 500 Motherboard PhotoIn addition to providing millions of chips to the electronics industry and computer manufacturers, MOS / CSG produced nearly all of the chips used in Commodore computers and floppy drives.  The notable exceptions to that statement were the Motorola 68000 used in the Amiga line and all memory.  Chuck explained that "...MOS tried to produce memory but just weren't any good at it". 

In the early 1980's Commodore hired dozens of notable engineers including Dave Haynie and Bill Herd to work in their in house "fab" but Commodore still refused to make significant investments in research and development.  Other similar sized companies would have hundreds of Engineers.

Under Jack Tramiel R&D was a secondary concern.  After Jack left in 1984 Commodore's money man, Irving Gould,  dramatically reduced they already spartan R&D budgets, in an effort to increase short term profits.  Commodore could have easily licenced Bill Mensch's 16bit version 6502 and they did consider it for the Amiga but in the end, managements desire to squeeze ever more profit out of existing technology, left MOS / CSG to languish with old technology.

By the mid 1980's MOS' best days were history and they were fully integrated into the Commodore structure.    With a few very important exceptions, MOS staff seemed content to manufacture what they had always manufactured.  By 1985 they were definitely looking to the past and had forgotten that theirs was a fast paced, dynamic industry.

CSG 4510 r5 CPU from a Commodore 65 PrototypeEven when Commodore began its struggle for survival, Management just did not see that they were living in an R&D business.  In 1990 Commodore started work on a secret project called the Commodore 65 and had MOS / CSG develop a new chip called the CSG 4510 which was little more than a slightly enhanced 8bit 6502 with two integrated 6526 I/O adapters. 

During the 1970's Allen-Bradley's MOS had installed a large underground cement tank to store the extremely hazardous waist chemicals produced during the chip manufacturing process.  By the early 1980's this tank had cracked and leached chemicals into the ground water.  Most of the surrounding residential neighbourhood used piped city water but several used well water. 

The problem was initially 'hushed up' and only a small number of CSG managers were aware of the problem.  In 1981 Commodore excavated some of the contaminated soil and in 1984 "household carbon units were installed at residences where at least 1 part per billion of VOC was detected".  By 1989 the US Environmental Protection Agency has started a serious investigation into the the problem.

An Unceremonious End
Commodore produced hundreds of millions of chips in the MOS Norristown fab. but in 1992 facing serious financial problems Commodore put the troubled facility into Bankruptcy protection.  Oddly, even though CSG was bankrupt, Commodore maintained the equipment in an effort to keep it functional. 

Immediately after the 1994 bankruptcy of Commodore International, the plant was sold to a group of its former managers for $5.3 million which included $1 million in expenses for things like EPA liens.  It was renamed GMT Microelectronics and at the height of that organizations success in 1999 its 180 employees produced and sold $21 million in product.  Two years later the EPA would force the famous Norristown fab to close and GMT's assets were liquidated.

Map to MOS Technology / CSG / Commodore Semiconductor Group 950 Rittenhouse Road, Norristown PAIn November of 2005 an EPA study shows the site had been clean for five years and as you can see from the satellite shot on the left, Google Earth shows that the building still exists today.

In the simplest of terms, MOS was Commodore and Commodore was MOS.  MOS was a precursor to Commodore.  It was a bell-weather foretelling Commodores future.  Together they soared and together they crashed.

Technical Notes
The 6500 line just keeps getting bigger under Bill Mensch.  He plans to start production of a new line of 6500's using RISC (Reduced Instruction Set) called "Terbium" (65th element in the periodic table) in early 2007.  It will be competition for the ARM7 32Bit RISC processor.

In September of 1983 Jim Butterfield wrote a nice summary of the 6503, 6504, 6505, 6506, 6507, 6509, 6510 (used in the Commodore 64), 6512, 6513, 6514, and 6515 chips for Compute magazine.  You can read his write-up clicking on the 6500 CPU's link on this page. 

The Technical Manual for the 6500 and 6502 are available on our Manuals page or by clicking HERE. The Technical Manual for MOS / CSG's 6509, is available in the same location or by clicking HERE

There are KIM-1 schematics, manuals and history on our Products, KIM1 page.   We also have scanned and OCR'd several interesting articles on the Pre-Commodore MOS KIM-1 in our Gallery, Magazines section.

Click HERE for schematics and instructions to Build your own MOS / CSG KIM1 with components you can still find in 2003.

A complete Commodore time line is available on our site HERE.

MOS also manufactured the Commodore ChessMate game.

Click HERE for a huge, but still partial, list of 6502 based machines.

MOS / CSG Timeline

August 1974

June 1975

  • MOS Technology announces the MC6501 at US$20 and soon after the MC6502 at US$25. This was truly breakthrough pricing; the Intel 8080 costs about US$150 http://www.aronsson.se/hist.html

  • MOS was able to produce the chips at this low price because they increased their yield dramatically by reducing flaws in their chips 'masks' before starting production.  Click HERE for details.

  • Motorola sues MOS Technology over the similarity of the 6501 and 6502 processors to the 6800. In an out-of-court settlement, MOS Technology withdraws the 6501 from the market. http://www.islandnet.com/~kpolsson/comphist/comp1975.htm

  • About the same time MITS ships one of the first PCs, the Altair 8800 with one kilobyte (KB) of memory, as a $397 mail-order kit. The machine and company have nothing to do with MOS but it gives you an idea of what was happening at that time.

  • The 6502 was not backward compatible with its Motorola 6800 inspiration but it was pin compatible and ran up to 4 times faster. 

Summer 1976MOS / CSG Commodore KIM1

  • MOS Technology Inc. announces the KIM-1 Microcomputer System, with 1-MHz 6502 CPU, 1KB RAM, 2KB ROM monitor, 23-key keypad, LED readout, cassette and serial interfaces, for US$245.

    • It was called a "Computer Trainer" but was largely designed as a demo machine for the MOS 6502 processor.

  • Chuck Peddle developed the PET concept and tried to sell it to Apple's Steve Jobs but Jobs did not offer enough money for it

  • Bill Mensch leaves MOS for consulting work in Arizona.

September 1976

  • Commodore PET 8296 AnnouncementCommodore announces it is buying MOS Technologies for US$60 Million so that it can become an almost completely self contained company.  Texas Instruments had provided processors for many Commodore calculators in the years previous and as Commodore made the business more successful, TI saw the opportunity.  TI stopped selling chips to Commodore and started selling Calculators directly.  Commodores supplier became Commodore's competitor and Jack Tramiel vowed this would never happen again.  Vertical Integration was the answer.

  • Click HERE to skip to the end of this page for a nice 1976 write up on Commodores Purchase of MOSGolden Commodore 64

1976 - 1985

  • MOS / CSG designs and produces chip after chip feeding 100% of Commodore product like the VIC20, Commodore 64, Commodore 128, Plus/4 and many more 

1977Commodore LCD

  • MOS co-founder Bill Mensch starts the WDC Western Design Center and produce proprietary versions of the 6502.  About 2 BILLION 65C02 processors have been integrated into everything from cell phones to kitchen stoves since the 25 years since.   (Unrelated to MOS / CSG)



  • Chuck Peddle leaves Commodore to work for Apple Computer and within months returnCommodore PET & More From 1983 Catalogs back to Commodore.
  • Commodore stops producing calculators

1983 - July 15th

  • Nintendo releases 6502 based ultra low cost Famicom Computer in Japan for just US$65.  In the US this device would be sold as the massively successful Nintendo Game System and would ship with the original Donkey Kong

1985 - 1994

  • Commodore starts to produce machines with Motorola chips (like the Amiga 1000, 500, CDTV...) but MOS / CSG is still a critical part of the Commodore machine



  • Under financial duress, Commodore closes its CSG Norristown, Pennsylvania fab

  • Although the Commodore Semiconductor Group declared bankruptcy, the company continued to maintain the equipment and systems at the plant, ensuring that the facility would not fall into disrepair and would remain attractive to a potential buyer.  http://www.antiquetech.com/companies/GMT%20Microelectronics%20Corporation.htm 

April 29th 1994

  • Commodore goes bankrupt and the MOS / CSG remnants goes up for sale.

September 2nd 1994

December 1994

  • US Environmental Protection Agency opens discussions with GMT about the plant



  • "The EPA is overseeing the cleanup of the Commodore Semiconductor Group site. Construction of the groundwater extraction and treatment system began in the fall of 1999. In February 2000, pipelines and underground wiring were installed, pumps were installed at each of the extraction wells, and the treatment building was constructed. The treatment process equipment was installed in May 2000. Preliminary start-up and testing of the system began in August 2000. The system started operations in September 2000 to remove volatile organic compounds (VOCs), the chemical components of solvents and degreasers, from the groundwater using several filtration and evaporation techniques. The treated groundwater is discharged to the Audubon Water Company’s distribution system for public water.
    http://epa.gov/reg3hwmd/npl/PAD093730174.htm http://epa.gov/reg3hwmd/super/PA/commodore/pad.htm