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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 2<sup>1</sup> 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, that isn't 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 communication, then called serial and also 2- or 4-bit 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<!-- SUBNEG (subtract and branch if negative) --> though it can emulate 20 [[MIPS architecture|MIPS]] instructions).<ref name="Courtland_2013"/>
== 1-bit ==
A [[serial computer]] processes data a single bit at a time. For example, the [[PDP-8|PDP-8/S]] was a [[12-bit]] computer using a 1-bit ALU, processing the 12 bits serially.<ref name="DEC_1969"/>
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* [[Bit slicing]]
* [[Turing machine]]
* [[Low Pin Count]] for 4-bit communication
** It's successor for modern computers, Intel's [[Enhanced Serial Peripheral Interface]] (eSPI) allows 1-bit, 2-bit, or 4-bit communication
== References ==
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