1-bit computing

In computer architecture, 1-bit integers or other data units are those that are 1 bit (1/8 octet) wide. Also, 1-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers of that size. There are no computers or microcontrollers of any kind that are exclusively 1-bit for all registers and address buses. A 1-bit register can only store 21 different values, i.e. 0 or 1 (off or on, respectively). This is very restrictive and therefore not enough for a program counter which, on modern systems, is implemented in an on-chip register, but is not implemented on-chip in some 1-bit systems. Opcodes for at least one 1-bit processor architecture were 4-bit and the address bus was 8-bit. While 1-bit computing is mostly obsolete, 1-bit serial communication is still used in modern computers, that are otherwise e.g. 64-bit, and thus also have much larger buses. While 1-bit CPUs are obsolete, the first carbon nanotube computer from 2013 is a 1-bit one-instruction set computer (and has only 178 transistors; since it has only one instruction though it can emulate 20 MIPS instructions). A serial computer processes data a single bit at a time. For example, the PDP-8/S was a 12-bit computer using a 1-bit ALU, processing the 12 bits serially. An example of a 1-bit computer built from discrete logic SSI chips is the Wang 500 (1970/1971) calculator as well as the Wang 1200 (1971/1972) word processor series developed by Wang Laboratories. An example of a 1-bit architecture that was marketed as a CPU is the Motorola MC14500B Industrial Control Unit (ICU), introduced in 1977 and manufactured at least up into the mid 1990s. Its manual states: [...] Computers and microcomputers may also be used, but they tend to overcomplicate the task and often require highly trained personnel to develop and maintain the system. A simpler device, designed to operate on inputs and outputs one-at-a-time and configured to resemble a relay system, was introduced.