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This Guy Designed and Built an 8-bit CPU from Scratch

The breadboard CPU can play the Mario theme, but programming it is a pain in the ass.

Daniel Oberhaus

Daniel Oberhaus

Image: Paulo Constantino/YouTube

Today, most modern computers use a CPU based on a 64-bit architecture. This basically means that the processors, memory and data buses all traffic in 64-bit blocks of information (a bit is binary unit of data—either a 1 or 0). But back in the early 1970s, cutting edge commercial CPUs like Intel’s 8008 processor relied on an 8-bit architecture.

These computers would seem remarkably primitive to modern users, but as YouTuber Paulo Constantino’s latest project goes to show, building an 8-bit CPU is still no small task.

To the untrained eye, Constantino’s project just looks like a tangle of wires. But all those wires are connected to breadboards—a small, hole-filled base used for prototyping electronic circuits—to create a homebrew 8-bit CPU.

According to Constantino, he designed the circuits on paper for two days and then actually built the CPU over the course of a week. Since the CPU isn’t able to be hooked up to a keyboard yet, Constantino had to program the device by flipping DIP switches, a row of ‘on-off’ switches that can be used to change the behavior of an electronic circuit. In the video above, Constantino shows a basic program to make the CPU count to 255. This process is shown by a row of eight electronic lights counting in binary in real time.

In a follow up video, Constantino also showed how the CPU could be used to play the Mario theme. For his next trick, he plans to integrate a keyboard into the system to allow for easier programming.