Specific examples of registers from various processors are used to illustrate the general nature of assembly language. For those with high speed connections, the very large single file summary is still on line. Most early computers had only one data register that could be used for arithmetic and logic instructions. Often there would be additional special purpose registers set aside either for temporary fast internal storage or assigned to logic circuits to implement certain instructions. Computers soon had multiple data registers, address registers, and sometimes other special purpose registers.
Some computers have general purpose registers that can be used for both data and address operations.
Many computers have additional control registers for implementing various control capabilities. Often some or all of the internal flags are combined into a flag or status register. The first computers typically only had one accumulator. Many times there were related special purpose registers that contained the source data for an accumulator. Accumulators were replaced with data registers and general purpose registers.