1-bit computing: Difference between revisions

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{{Use list-defined references|date=June 2022}}

{{Computer architecture bit widths}}

[[File:MC14500BCP.jpg|thumb|1-bit [[programmable logic controller]] [[Motorola MC14500B|MC14500BCP]]]]

In [[computer architecture]], '''1-bit''' [[integer (computer science)|integer]]s or other [[Data (computing)|data]] units are those that are {{nowrap|1 [[bit]]}} (1/8 [[octet (computing)|octet]]) wide. Also, 1-bit [[central processing unit]] (CPU) and [[arithmetic logic unit]] (ALU) architectures are those that are based on [[processor register|register]]s of that size.

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There are no computers or [[microcontroller]]s of any kind that are exclusively 1-bit for all registers and [[address bus]]es. A 1-bit register can only store two different values. 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. [[Opcode]]s 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 (research) [[carbon nanotube computer]] from 2013 is a 1-bit [[one-instruction set computer]] (and has only 178 transistors; since it has only one instruction<!-- SUBNEG (subtract and branch if negative) --> though it can emulate 20 [[MIPS architecture|MIPS]] instructions).<ref name="Courtland_2013"/>

== 1-bit ==

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Other examples of 1-bit architectures are [[programmable logic controller]]s (PLCs), programmed in [[instruction list]] (IL).

Such as the 1969 [[PDP-14]].<ref name=CHD>

{{cite web |url=http://www.chdickman.com/pdp14 |title=DEC PDP-14 Industrial Controller}}

</ref>

Several early [[massively parallel]] computers used 1-bit architectures for the processors as well. Examples include the May 1983 [[Goodyear MPP]] and the 1985 [[Connection Machine]]. By using a 1-bit architecture for the individual processors a very large array (e.g. the Connection Machine had 65,536 processors) could be constructed with the chip technology available at the time. In this case the slow computation of a 1-bit processor was traded off against the large number of processors.