MOS Technology

MOS Technology, Inc.
Company type	Private (originally), later subsidiary of Commodore Business Machines
Industry	Semiconductor
Founded	1969 in Valley Forge, Pennsylvania, U.S.
Founder	John Paivinen, Mort Jaffe, Don McLaughlin
Fate	Acquired by Commodore Business Machines in late 1976; later became Commodore Semiconductor Group and then GMT Microelectronics
Headquarters	Audubon, United States
Area served	Worldwide
Key people	Chuck Peddle (chief engineer after acquisition), Bill Mensch (engineer)
Products	6502 microprocessor and related chips, calculator ICs, video interface chips, peripheral interface adapters
Number of employees	183 (as GMT Microelectronics in 1999)
Parent	Commodore Business Machines (after 1976)

MOS Technology, Inc.—abbreviated as "MOS" from Metal Oxide Semiconductor—later operated under the names CSG (Commodore Semiconductor Group) and GMT Microelectronics. This semiconductor company, headquartered in Audubon, Pennsylvania, gained prominence for developing the 6502 microprocessor along with several other chip designs that powered Commodore International's home computer series.

History

In 1969, three former executives from General Instrument—John Paivinen, Mort Jaffe, and Don McLaughlin—established MOS Technology in Valley Forge, Pennsylvania. The Allen-Bradley Company, aiming to secure an alternative source for electronic calculator chips originally designed by Texas Instruments (TI), acquired a controlling interest in MOS Technology in 1970.

During the early 1970s, Texas Instruments began selling complete calculators at prices below their individual chip costs, which destabilized many chip producers reliant on calculator components. To withstand this market shift, MOS diversified its offerings and became a supplier to Atari, providing a custom single-chip solution for the Pong game system.

A significant turning point came in 1975 when several engineers from the Motorola 6800 project left Motorola after management discontinued efforts on a cost-reduced version of that CPU. At a time when semiconductor foundries were scarce, these designers joined MOS Technology—a modest yet capable East Coast firm. Led by Chuck Peddle and including notable engineer Bill Mensch, this group created a new microprocessor intended to surpass the 6800 in performance while being more economical. Their creation, the 6501, featured design simplifications that allowed it to operate up to four times faster than the 6800.

Mask fixing

Earlier microprocessors such as the 6800 were fabricated using a contact aligner, which required placing the photomask directly onto the silicon wafer. This method caused rapid mask wear, limiting production runs to roughly a dozen copies and yielding only about 10% functional chips.

In 1974, Perkin-Elmer introduced the Micralign projection scanner technology, which projected the mask image without physical contact with the wafer. This innovation extended mask durability to thousands of uses and improved chip yield rates to approximately 70%. The resulting cost reduction was dramatic; for instance, the price of the 6800 dropped from to , despite no changes in its design.

The Micralign also streamlined mask replacement processes since only one mask per aligner was necessary, thereby reducing both expenses and turnaround time for design corrections. MOS Technology further advanced manufacturing by inventing a mask "fixing" technique that enabled them to remove flawed masks, repair them, and reinsert them into production. This approach allowed early batches of new CPUs—including the 6502—to achieve success rates exceeding 70%, enhancing both reliability and cost-effectiveness.

6502 family

Following the summer 1975 announcement of the 6501 processor, Motorola filed a lawsuit against MOS in November due to the 6501’s pin compatibility with the 6800 motherboard despite lacking instruction compatibility. By March 1976, MOS resolved the dispute by discontinuing sales of the 6501 and compensating Motorola .

Concurrently, MOS introduced the 6502 in September 1975 at an unprecedented price of . Operating at , it differed slightly from the 6501 by including an integrated clock oscillator and modified pin assignments but delivered superior performance compared to more complex processors like the 6800 and Intel 8080, all while costing significantly less. Although it was incompatible with existing Motorola hardware platforms, its affordability quickly gained widespread acceptance.

The low price point of the 6502 surprised many industry observers at its debut trade exhibition; prevailing yield standards suggested it should have been priced higher. In response, competitors Motorola and Intel reduced their prices from to , confirming the disruptive impact of the 6502 and accelerating its adoption across markets.

The processor quickly became popular and was licensed by firms such as Rockwell International, GTE, Synertek, and WDC. Variants numbered from 6503 through 6507 offered cost savings by reducing pin count; notably, the 6507 powered devices like the Atari 2600 console and related disk drives. Other models (6512–6515) utilized external clock inputs suited to systems with onboard timing sources. The hybrid 6510, which incorporated additional input/output ports, was a key component of the Commodore 64 computer platform.

Commodore Semiconductor Group

Although the 6502 chip achieved considerable success, MOS Technology encountered financial strain when the calculator integrated circuit market collapsed. Commodore Business Machines (CBM), which also suffered significant setbacks due to Texas Instruments entering the market, secured fresh investment and supported critical suppliers such as MOS to ensure a steady supply of integrated circuits.

In late 1976, CBM, with a market value near , purchased MOS, valued at about , through an all-stock transaction. Shareholders of MOS received a 9.4% ownership interest in CBM, contingent upon Chuck Peddle joining as chief engineer. Following the acquisition, MOS functioned as Commodore’s manufacturing division but initially kept its original name to avoid the cost of reprinting documentation. Eventually, this division was rebranded as the Commodore Semiconductor Group (CSG), although chips continued to display the "MOS" logo until mid-1989.

Prior to being acquired, MOS had created the KIM-1 computer kit to demonstrate the capabilities of the 6502 processor. After joining Commodore, Peddle convinced owner Jack Tramiel to redirect efforts from calculators toward home computers, foreseeing rapid expansion in that sector. However, internal lack of enthusiasm caused fragmentation within teams; notably, the 6522 (VIA) chip remained undocumented for several years.

Bill Mensch left MOS before the acquisition and established the Western Design Center (WDC) in 1978. Licensed to produce 6502 processors, WDC developed CMOS variants such as the 65C02 with bug fixes and reduced power consumption and introduced the 16-bit 65816 processor compatible with an 8-bit mode. WDC migrated much of MOS’s product line to CMOS technology, ensuring the 6502’s ongoing use in embedded applications like medical equipment and automotive control systems.

GMT Microelectronics

After Commodore declared bankruptcy in 1994, its semiconductor division—formerly MOS and then CSG—was acquired by former executives for approximately , plus an additional for costs including an EPA license. Dennis Peasenell assumed the role of CEO. In December 1994, the EPA entered into a Prospective Purchase Agreement with GMT Microelectronics that limited liability in exchange for sharing cleanup responsibilities. Operating under the name GMT Microelectronics (Great Mixed-signal Technologies), the company reopened MOS Technology’s original circa-1970 one-micrometre fabrication facility in Audubon, Pennsylvania, which Commodore had shut down in 1993.

The facility had been listed on the EPA’s National Priorities List since 1989 due to a 1978 trichloroethylene (TCE) leak from an underground tank used for semiconductor cleaning processes, contaminating nearby groundwater with TCE and other volatile organic compounds (VOCs). By 1999, GMT Microelectronics reported revenues of , employing 183 personnel at this location. That year, GMT announced foundry services utilizing TelCom’s Bipolar and SiCr Thin Film Resistor technologies and became an authorized alternative source for TelCom’s Bipolar products. Production capacity reached 10,000 five-inch semiconductor wafers monthly, fabricating CMOS, BiCMOS, NMOS, bipolar, and silicon-on-insulator (SOI) devices.

GMT Microelectronics ceased operations in 2000 and abandoned its assets at the former Commodore Semiconductor Group superfund site.

Chip identification system

The majority of MOS integrated circuits adhere to a naming system that reflects the employed technology (logic gate architecture):

NMOS (M65xx)
CMOS (M65Cxx)
HMOS (M75xx)
HMOS-2 (M85xx)

Product lineup

KIM-1 – single board computer and CPU evaluation platform utilizing the 6502 processor
2521 – calculator chip supporting 8-digit display
2523 – 8-digit calculator integrated circuit
2529 – scientific calculator array implemented on a single chip
4510 – CPU (CSG 65CE02) incorporating dual CIAs on-chip; operates at 3.45 MHz
4567 – VIC-III Video Interface Chip
5719 – Gary Gate Array chip
6501 – CPU compatible in pinout with Motorola 6800
6502 – CPU resembling the 6501 but lacking compatibility with the 6800 pin configuration
65CE02 – CPU variant derived from the 6502 design
6503 – CPU featuring 12 address pins along with NMI and IRQ inputs
6504 – CPU equipped with 13 address pins and an IRQ input
6505 – CPU containing 12 address pins, plus IRQ and RDY signals
6507 – CPU with a total of 13 address pins
6508 – CPU integrating 256 bytes of RAM and eight I/O pins
6509 – CPU offering 20 address pins
6510 – CPU featuring clock inputs and integrated I/O ports
6520 – PIA Peripheral Interface Adapter chip
6522 – VIA Versatile Interface Adapter device
6523/6525 – Tri-Port Interface chip family
6526/8520/8521 – CIA Complex Interface Adapter series
6529 – SPI/SPIA Single Port Interface Adapter chip
6530 – RRIOT combining ROM, RAM, I/O, and Timer functions
6532 – RIOT RAM-I/O Timer integrated circuit
6540 – chip containing a 2 KiB ROM memory block
6545 – CRTC CRT Controller device
6550 – Static RAM with a capacity of 512 bytes
6551 – ACIA Asynchronous Communications Interface Adapter unit
6560 – VIC Video Interface Chip designed for (NTSC) systems
6561 – VIC Video Interface Chip tailored for (PAL) with Revision: -101 / E
6562 – VIC Video Interface Chip (NTSC) variant supporting a 40-column display mode (6561 derivative)
6564 – video chip enabling an 80-column display (used in Colour PET, partially incorporated into MOS 6560/6561)
6566 – VIC-II variant used in MaxMachine systems
6567 – VIC-II for NTSC video format, Revisions: R56A/R7/R8/R9
6569 – PAL version of the VIC-II, Revisions: R1/R3/R4/R5 (noting R1 supports only five luminance levels)
6570 – microcontroller utilized on Amiga 500 keyboard PCB, revision -036
6572 – VIC-II supporting PAL-N standard
6573 – VIC-II designed for PAL-M video format
6581/6582/8580 – series of SID Sound Interface Devices by MOS Technology
7360/8360 – TED Text Editing Device versions HMOS-I and HMOS-II
7501 – HMOS-I based CPU derived from the 6502, including a seven-bit I/O port
8361 – AGNUS Address Generator Unit for (NTSC) systems
8362 – DENISE Display Encoder chip
8364 – PAULA unit providing Port Audio UART and Logic functions
8367 – AGNUS Address Generator Unit designed for (PAL) systems
8370, along with variants (8371,8372,8373,8375)– "Fat" AGNUS and ECS AGNUS/DENISE components for the Amiga Enhanced Chip Set
8374 – AGA ALICE Address Generator Unit
8500,8501,8502 – HMOS-II CPUs based on the architecture of the 6510, including models running up to two megahertz
8520 – CIA Complex Interface Adapter employed in Amiga systems operating at frequencies up to two megahertz
8551 – HMOS-II version of the ACIA communications interface adapter
Multiple VIC-II chips (8562,8564,8565,8566) designed for NTSC and PAL television standards
Various VDC Video Display Controllers such as (8563,8568)
Additional components include clock generator (8701), PLA (8721), MMU Memory Management Unit (8722) and DMA controller (8727)

External links