Bit slicing is a method of combining processor modules to multiply the word length. Bit slicing was common with early processors, notably the AMD (Advanced Micro Devices) 2900 series that originated in 1975.
In a bit-sliced processor, each module contains an ALU (arithmetic-logic unit) usually capable of handling a 4-bit field. By combining two or more identical modules, it is possible to build a processor that can handle any multiple of this value, such as 8 bits, 12 bits, 16 bits, 20 bits, and so on. Each module is called a slice. The control lines for all the slices are connected effectively in parallel to share the processing "work" equally.
Prior to about 1980, experimenters used bit slicing to create more powerful computers than were generally available at the time, without resorting to available (but expensive) 16-bit processors. Some experimenters built processors as wide as 64 bits using this technique. More recently, bit slicing has been used in specialized encryption methods such as block ciphers.