The Rise of
MOS Technology & The 6502
Written by Ian Matthews of
February 15, 2003
Seriously revised and expanded on January 18, 2006, Last update June 26,
Last minor update: June 4, 2007
At 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
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
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.
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
manufactures, 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
took six other key Motorola 6800 engineers to work for an old General
Electric colleague who ran a small "fab" called MOS Technologies.
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.
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
a year the team developed the CPUs line that would change the world; The MOS 6500
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
www.commodore.ca , Chuck said "Bill ...was like a layout savant...
he can just picture an entire layout in his head."
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
this picture). Bill said that one of the 6502 pins is
officially named SO (Set Overflow). "Chuck, Rod, and I know
real name is Sam Orgill... Rods dog".
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.
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.
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.
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."
Star is Born: The 6502
MOS designed and manufactured two 6502 trainers call the
(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.
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.
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."
founder and CEO,
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,
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
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.
Over 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
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
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.
& The Rise of 16Bit
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
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
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
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
System. The 6502 was also used in many of the
original arcade video games like
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
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.
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
C128 Engineer) quit and went to work for a chip
small design shop, he was shocked that he could not simply order up new
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.
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
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.
Even when Commodore began its struggle for survival, Management just did
not see that they were living in an R&D business.
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
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
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.
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
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.
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.
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
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
There are KIM-1
schematics, manuals and history on our Products,
We also have scanned and OCR'd several interesting articles on the
Pre-Commodore MOS KIM-1 in our
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
MOS also manufactured the Commodore ChessMate game.
HERE for a
huge, but still partial, list of 6502 based machines.
MOS / CSG
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
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
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.
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
The 6502 was not
backward compatible with its Motorola 6800 inspiration but it was pin
compatible and ran up to 4 times faster.
MOS Technology Inc.
KIM-1 Microcomputer System, with 1-MHz 6502 CPU, 1KB RAM, 2KB ROM
monitor, 23-key keypad, LED readout, cassette and serial interfaces, for
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
leaves MOS for consulting work in Arizona.
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
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
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
- Chuck Peddle leaves Commodore to work
for Apple Computer and within months returns 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
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
April 29th 1994
September 2nd 1994
"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.