The 1-bit architecture is a microprocessor or computer architecture that has a datapath width or a highest operand width of 1 bit. These architectures typically have a matching register file with registers width of 1 bit. Very few 1-bit architecture CPUs were commercially marketed.
1-bit MPUs and MCUs found some success in industrial equipment where actual calculations was not needed but simple Boolean operations dominated the majority of the task. Many industrial controllers do things based on very simple conditions such as sensor threshold activation or button press. Consequently 1-bit MPUs and MCUs found a unique niche use as programmable logic controllers. For such applications, MCUs and MPUs continued to be manufactured well into the 1990s.
For general purpose applications and other calculations-related applications, 1-bit was largely seen as obsolete even in the early 1970s. Most bit-serial applications quickly switched over to 4/8-bit and then 16-bit microprocessors, if not simply due to their low cost. Today all 1-bit microprocessors are largely obsolete, even academia.