Famous Apple chip studied by digital archaeologists

Editor’s Note: The following article is reprinted from TechWorld.

A team of chip archaeology enthusiasts is making headway on “imaging” for posterity the hugely-influential but now little-understood MOS 6502 chip that almost single-handedly launched the home computer and games console revolution a generation ago.

If the 8-bit 1MHz MOS Technology 6502, designed by Chuck Peddle in 1975, doesn’t trip off the tongue to the average Internet user, its influence on computing history is still immense.

A MOS 6502 Processor (Source: CPU-Collection.de via Wikipedia)

Invented to undercut the cosy duopoly of Intel’s 8080 and Motorola’s 6800 (previously also designed by the MOS team), the 6502 was eventually used in the Apple 1 and II, the Commodore PET, and the Atari 2600 and the Nintendo Entertainment System (NES) game consoles that changed the course of digital entertainment.

The 6502 was also at the heart of the BBC Micro that kick-started home computing in the UK and was a big influence on the ARM chip designs that now power many of the world’s most famous smartphones, including the Apple iPhone.

Famously, the chip was said to power Arnold Schwarzenegger’s Terminator and, in a wholly ironic fashion, Bender the alcoholic robot in Matt Groening’s cultish animation series, Futurama.

Although emulators for the chip exist, these are an approximation that can’t model exactly what is happening on the microprocessor at transistor level.

The MOS 6502 chip was used in the Apple II, among many other early home computers and game consoles.

According to the chip techies at visual6502.org—engineers Greg James, Barry Silverman, and Brian Silverman—the only way to glean in-depth understanding of the chip is to strip away the polysilicon layers of the chip using acid, photographing the results in high-resolution.

As well as revealing the inner structure of the chip in great detail, this also allows a three-dimensional understanding of the chip’s 20,000 interior components that can be used to build a working model of its operation.

“While a multitude of people understand the instruction set for the 6502, almost no one, apart from the original designers, understands how the physical chip achieves this instruction set,” says a blog on the group’s Website.

The techies have also turned their discovered knowledge of the chip into a Javascript html 5 simulation that steps through the 6502’s inner digital workings. The authors warn that it requires at least 2GB of RAM and is not compatible with Internet Explorer.

The team openly describe themselves as ‘chip archaeologists’ and have imaged a number of other ancient chips—the Intel 4004, the Zilog Z80 and Motorola’s 6800—which they hope will give future researchers a better understanding of the ever more remote birth of the digital age.

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