Commodore 64

Release date - August 1982; 40 years ago.

Operating system

  • Commodore KERNAL/BASIC 2.0

MOS technology 6510/8500

  • @ 1.023 MHz (NTSC version)
  • @ 0.985 MHz (PAL version)


  • 64KB(65,536 bytes) - RAM + 20 KB ROM


  • VIC-II(320×200, 16 colors, hardware sprites, raster interrupts)


SID (3× osc, 4× Wave, filter, ASDR, Ring)

Brief History of Commodore 64

The  64 began its life in January of 1981 when MOS Technology Engineers decided they needed a new chip project. MOS’ Albert Charpentier had been responsible for several of the highly successful VIC-20 chips. 


Albert Charpentier

“We were fresh out of ideas for whatever chips the rest of the world might want us to do. So we decided to produce state-of-the-art video and sound chips for the world's next great video game”.

By November of 1981, the chips were completed but Commodore’s president Jack Tramiel decided against using them in the faltering arcade game market.  Instead he tasked the engineers with developing a 64 kilobyte home computer for show at the Winter Consumer Electronics Show (CES) the second week  of January 1982, just 6 weeks away. 

Two days after Jacks' request, the basic design was completed and by the end of December 1981 the hardware for five VIC-30 (the C64’s development name) prototypes were assembled. In the remaining two weeks, the VIC-20 operating system with lowly Commodore Basic 2.0 was stretched onto the C64. It did not hurt that there were no other new powerful computers shown at CES by Commodores competitors that year.  

In addition to being vastly more powerful than anything on the market at the time, it was drastically cheaper than its competitors like the Apple II, IBM PC, or Radio Shack TRS-80.

The Commodore 64 is arguably the easiest to use programmable computer that has ever been made.  Like the PET and VIC-20 before it, the 64 booted to a friendly screen with the Commodore Basic Operating System ready and waiting for instruction.  If writing your own programs was too daunting and loading software from cassettes or floppies was ‘just too much’ for you, you could just jam a cartridge in the back of the unit and like magic your machine was doing whatever you wanted it to.

Creating the best selling machine in history is no small feat. They pushed the industry to a level of scale that was previously thought impossible.

Like its VIC-20 predecessor, the 64 was the first computer that millions of today’s programmers, designers, engineers and enthusiasts had ever used.  It has inspired a countless volume of software and hardware that we use today.

MOS 6500 

Within that first 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 , Chuck said “Bill …was like a layout savant… he can just picture an entire layout in his head.”

When asked Chuck, said about it in March 2007... “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. 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”.

In the 1970’s, 70% of the industries chips produced were detected as defective at the factory.  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 and 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.

The  6510

The  6510 is a 6502, except  that addresses 0000 and 0001 have special functions. There’s an input / output  port built into the chip: eight pins marked Po to P7 are available on the  microprocessor chip itself. Address 0000 is used as the direction register of  the 1/0 port, and 0001 is the port itself. Otherwise, the  6510 is identical to a  6502.

What does this mean to the Commodore 64?

First of all, locations 0000 and 0001 are no longer, RAM. PET uses these locations to hold the USR jump; on  the Commodore 64, this jump has been moved to address hex 0310 (784 decimal).  Second, you may use address 0001 to test I interrupts and control some of the 64’s  activities. For  example, you can sense if the cassette tape switch is down by checking PEEK(I)  AND 16. The three lowest-order bits are used for switching out ROM and switching  in RAM. Don’t ever do this from BASIC, and use prudence if you do it from  machine language. More on these bits in a moment.

A little more information on  memory control from address 0001: bit 0, mask 1, controls the BASIC ROM in addresses AOOO-BFFF. Switch this bit to zero and the BASIC ROM is gone: in its  place is RAM. Now you can write your own language. Bit 1, mask 2, controls the Kernal ROM in addresses EOOO-FFFF. Switch this bit to zero and the Kernel is gone, be very careful, since you’ve just 1 switched away all of the programs  that support I interrupts, keyboard, screen, and so on. If you switch off both  bits 0 and 1, you will get a 64K RAM machine: the I/O block will be switched  out, too.

The 6510 Central processor and chipset.  Was a standard  .9875 MHz  6502 (used in the KIM-1  and PET) with a additional input/output port and  the ability to see allot more RAM.  As part of the “next great video game” concept, Albert Charpentier recruited another MOS engineer Robert Yannes in 1981 to help figure out how far other companies could push their current technology.  By their own admission, they pulled apart and ‘stole’ ideas from Texas Instruments TI-99's, Atari 800's, Apple II's and others.  It is worth noting that most computers of the day used Commodore / MOS' powerful but inexpensive 6502 processor

According to Charles Winterable, Commodore’s  Worldwide Engineering Director, “We defined in advance the die size that would  give a yield we were willing to live with.  …Then we prioritized a wish  list of what needs to be in there to what ought to be in there to what we  would like to be in there.  …When he ran out of registers, he stopped.”  With two draftsman and a CAD technician they developed “first silicon” in just 9 months and shockingly it worked on the first try.

The VIC-II 6567 video chip in the 64 can produce about 128 colours but was only engineered for, and only officially supported, 16 colours.  “The width of each pixel is almost half of the NTSC colour clock, so when you alternate the pixels of two different colours, instead of getting the two colours that you think you’re getting you get a whole new phase interpretation”  Brian Dougherty, President of Berkley Software explained.  It displayed a large 320 x 200 character count.

The now legendary SID 6581 sound chip was astounding for its time.  It could play three different “voices” in sophisticated patterns and with some tinkering could be made to create one or two more.  It was without doubt the best sounding computer on the market at any price for years to come.  It was also likely the first computer in the world capable of reproducing a recognizable human voice without  the addition of peripheral hardware.

The most common C64 chip question is why does the screen say 38,911 bytes free when it supposedly has 64,000 bytes of memory.   This is because nearly half of its memory is used for internal functions like Commodore Basic 2.0.

Engineering flaws and supplier problems caused all kinds of issues with the early 64’s.  Some of the quality issues were simply caused by the C64’s enormous popularity.  One engineer is quoted as saying “You pick a switch that is listed as a  ‘consumer switch’.  You design it in.  …Then the production division wants 50,000 a week but the manufacturer says ‘We  can’t make that quantity.’ ”

Because production of 64 circuit boards was designed for the “auto-insertion” VIC-20 factory in the US, there were problems from day one with the Japanese plant which used manual-insertion production lines.  Local standards also wreaked havoc; the Japanese used mainly metric screws while the US lines worked with ‘English’ screws so when components were shipping between facilities, the result was not always pretty.  “It takes a very tough person to say ‘I’m not shipping these because they’re not as good as they could be – especially when people are clamoring to buy them” explained Charpentier.

There was a so called ‘sparkle’ problem which caused small ‘lights’ to appear on the screen of the first few hundred thousand  units.  Most thought the problem was caused by defects in the video chip but in fact the problem was voltage spikes caused by a series of 64 systems that adversely affected the ROM chip.  This same MOS ROM had been used in 3 million other computers including the wildly popular arcade game “Asteroids”, without problem.

Depending on the colours, the edges of some objects would appear slightly out of line because Charpentier miscalculated the number of clock cycles on each horizontal video line.  “Instead of 65 clock cycles per line, I had 64”.  This problem took five months to correct.

“They don’t test.  I’ve opened up brand-new Commodores and found traces cut.  They obviously use a power screwdriver to assemble the C-64, sometimes miss the screw and chop the traces.”  criticized one of Epyx Software staffers.

To top this off Commodore had moved its engineers to Head Office in Pennsylvania, away from the California production line which caused communication to be further strained.

Although the machine had important flaws, the Commodore 64 design team created a fantastic machine at very low cost which soundly thrashed the competition for years.  How did they do it  and why would it prove to be nearly impossible for Commodore (and most other companies) to replicate process in the future?   The design success is widely attributed to the fact that engineers were not intending to build a computer, just some chips, so the corporate bureaucrats left them alone.  Engineers did the core market research and developed their own standards.

The 64 was the last machine Commodore engineered on a whim.  “If you let Marketing get involved with Product Definition,  you’ll never get it done quickly.  And you squander the ability to make something unique…” said Winterable.  “When you get many people involved in a project, all you end up doing is justifying yourself… The  freedom that allowed us to do the C64 project will probably never exist again…”

The Commodore 64 was alive: it was immediately ordered into production which hit full stride by August 1982.

Commodore 64

Original C64 and some modern alternatives.