Archaeology Magazine - July/August 2011 - 33

The 6502 (and its slight variants) were used in systems such as (from top to bottom) the Commodore 64, Apple II, Nintendo Entertainment System, and the Atari 2600 gaming console.

vitual map includes the precise position and shape of each component in each layer of the chip, clearly identifying components like metal wires, transistors, and vias (holes in layers that allow wires to pass through and connect two levels). James sent these full circuit extraction drawings to Barry and Brian Silverman. The brothers translated James’ circuit model into an inventory of the 6502’s components and connectivity (spelling out which component is connected to which other ones). This detailed list, called a “netlist,” is essentially the 6502. The Silvermans then created a simple web-based simulation in which the virtual chip is turned on and allowed to run. A signal sent to a single input of the virtual chip causes certain transistors to ﬂip on and oﬀ, which is shown in the simulation by changing the transistor’s color. These switches trigger other transistors to ﬂip, causing a cascade as information steps through the chip. Eventually, the switches settle and the signal dies out. Then a new signal starts and runs a diﬀerent course. How each cascade proceeds demonstrates how diﬀerent parts of the chip are connected and the state the chip is left in after a cascade, each of which demonstrates how a diﬀerent computation is done. One Bay Area 6502 fan who saw the simulation obtained the netlist from the Visual 6502 team and fed the description into a “chameleon chip” called a ﬁeld programmable gate array that consists of many transistors that can be programmed to connect in diﬀerent ways. By lending the chameleon the characteristics of a 6502, he was able to hook it up to an old Atari 2600 and run games. “That means that we don’t need actual 6502 chips to drive old hardware or to study how old hardware works,” explains James.“We’re not crippled by the fact that the original 6502 is no longer being made.”

he pace at which the computer industry moves causes new technology to become obsolete within a matter of years. The more than 35 years since the release of the 6502 has seen a complete shift in the way people interact with technology. “Arguably every new technology transforms our rapport with our world,” says Witmore, the Texas Tech archaeologist.“They’re really prosthetics of humanity.” Think about a movie like Back to the Future. Marty McFly

may have been overwhelmed by what he saw in 2015, but had his son from the future been suddenly transported back to 1985, he would have been just as befuddled when placed in front of a Commodore. “The only thing that comes close to replicating the rate of growth in the electronics and computing ﬁelds is bacteria,” says Dag Splicer, a senior curator at the Computer History Museum in Mountain View, California. Indeed, since the release of the 6502, which contained 3,500 transistors, the sophistication of microprocessors has advanced by many orders of magnitude. In 1965, Gordon Moore, the cofounder of Intel, predicted that the number of transistors that chip designers could stuﬀ onto a “single silicon chip” would double every year at least until 1975. His prediction was accurate far beyond that point. Intel’s current top-of-the-line desktop computer microprocessor, the Intel Core i7, has more than 700 million transistors—right in the neighborhood of what Moore’s Law would predict. “Modern chips have something like 10 layers of metal all stacked up on each other,” James says, allowing for more transistors and more computing power. As these advances keep coming, the devices of the present quickly become relics of the past. “Digital media will not survive by accident,” explains Witmore. “If you leave a 3.5inch ﬂoppy disk in a tomb next to a rolled-up papyrus, you can unroll that papyrus and engage with it in a way that you can’t with a ﬂoppy, which requires you to bring other materials to bear,” like a particular computer or knowledge of a chip capable of reading the data on the disk. While there is no formal protocol for preserving our digital technologies, the Visual 6502 team is expanding its work to other chips, such as the Motorola 6800, which the 6502 undercut with its lower price point. James has also excavated and photographed the other two chips in his Atari 2600—one drove the graphics display and the other handled joystick inputs. One of the team’s future projects is to preserve an entire Commodore 64 system, which means not only excavating its chips, but also characterizing its motherboard, the circuit board that connects the CPU with the chips that control sound, inputs/ outputs, and control the disk drives. “People take for granted that our digital artifacts are going to be preserved,” says Visual 6502’s Barry Silverman. “To preserve an exact copy is not that easy. It’s got to be an active process.” ■ Nikhil Swaminathan is a senior editor at Archaeology.
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Archaeology Magazine - July/August 2011

Table of Contents for the Digital Edition of Archaeology Magazine - July/August 2011