His Nibbler implements a 4-bit CPU using 7400 logic chips. Because he’s come up with the architecture himself he’s taking a lot of steps to check all of his work before committing to a PCB.

Enter the DDL-4-CPU, courtesy of [Dave’s Dev Lab]. The DDL-4 is a project to build a modular 4-bit CPU using bitslice methods. This is where computations are broken down into simple operations ...

Yes, over half a century ago now, the Intel 4004 appeared in all its 4-bit glory (with its successor being the Intel 8080, ...

An earlier logic chip used as a building block for CPUs. Bit slice processors used arithmetic logic units (ALUs) that typically came in 4-bit increments, although 1- and 2-bit devices were also made.