#computing history

An implementation of "Difference Engine Number Two", a mechanical computer designed by Charles Babbage in 1847 but never completed.

Starting in 1985, a group of researchers at the London Science Museum began building a working version of the difference engine, completing it eventually in 2002.

A second version being demonstrated here in the photo was built for the Computer History Museum in Mountain View, California. These machines are capable of solving complex polynomial equations and contain structures that are still used to this day in modern computers, such as a "Mill", which is essentially the arithmetic logic unit of a CPU, and the "Store", which holds intermediate computational results and is akin to registers of a CPU. The machine even includes a working printing device, to show output.

You can run it in your browser here.

(^Commodore Colt)

From 1984-1991, Commodore manufactured and sold their own PC computers, alongside their own C64/128 and Amiga computers.

Well outside that one AVGN meme, half-bit isn't really a thing, but the answer is a bit weirder in other ways! The current most prominent CPU designs come from Intel and AMD, and Intel did produce 4-bit, 8-bit, 16-bit, 32-bit and 64-bit microprocessors (although 4-bit computers weren't really a thing). But what came before 4-bit microprocessors?

Mainframes and minicomputers did. These were large computers intended for organizations instead of personal use. Before microprocessors, they used transistorized integrated circuits (or in the early days even vacuum tubes) and required a much larger space to store the CPU.

And what bit length did these older computers have?

A large variety of bit lengths.

There were 16-bit, 32-bit and 64-bit mainframes/minicomputers, but you also had 36-bit computers (PDP-10), 12-bit (PDP-8), 18-bit (PDP-7), 24-bit (ICT 1900), 48-bit (Burroughs) and 60-bit (CDC 6000) computers among others. There were also computers that didn't use binary encoding to store numbers, such as decimal computers or the very rare ternary computers (Setun).

Boards of Canada played on a 1959 PDP-1 Computer

Audio is produced on the PDP-1 with a clever hack done by Peter Samson as a student at MIT in the early 1960s. The PDP-1 has six "program flags", which are 6 flip-flops wired to six light bulbs on the control panel. A CPU instruction provides the ability to turn these light bulbs on or off via software. While these bulbs were originally intended to provide program status information to the computer operator, Peter repurposed four of these light bulbs into four square wave generators (or four 1-bit DACs, put another way), by turning the bulbs on and off at audio frequencies. Four wires are attached to the signal lines for these light bulbs. Resistors are used to downmix these four signals into stereo audio channels and provide impedance matching into a standard stereo amplifier, and combined with capacitors to create low pass filters to cut out the buzz of the computer noise and soften the square waves. The four light bulbs act as individual music voices. Each voice is transcribed separately using a custom DSL defined for the 1962 Harmony Compiler, and then merged into a single file which is then compiled by the original Harmony Compiler running on a PDP-1 emulator. The resulting paper tape file is then punched to physical paper tape using a tape punch, and then loaded into the real PDP-1 for music playback.

Samson also contributed to Spacewar!, one of the earliest videogames.