Digital electronics
Computer design
### Computer design

[thumb\|Intel 80486DX2 [microprocessor](/wiki/Microprocessor "Microprocessor")](/wiki/File:80486dx2-large.jpg "80486dx2-large.jpg")

The most general\-purpose register\-transfer logic machine is a [computer](/wiki/Computer "Computer"). This is basically an [automatic](/wiki/Automaton "Automaton") binary [abacus](/wiki/Abacus "Abacus"). The [control unit](/wiki/Control_unit "Control unit") of a computer is usually designed as a [microprogram](/wiki/Microprogram "Microprogram") run by a [microsequencer](/wiki/Microsequencer "Microsequencer"). A microprogram is much like a player\-piano roll. Each table entry of the microprogram commands the state of every bit that controls the computer. The sequencer then counts, and the count addresses the memory or combinational logic machine that contains the microprogram. The bits from the microprogram control the [arithmetic logic unit](/wiki/Arithmetic_logic_unit "Arithmetic logic unit"), [memory](/wiki/Memory "Memory") and other parts of the computer, including the microsequencer itself. In this way, the complex task of designing the controls of a computer is reduced to the simpler task of programming a collection of much simpler logic machines.

Almost all computers are synchronous. However, [asynchronous computers](/wiki/Asynchronous_computer "Asynchronous computer") have also been built. One example is the [ASPIDA DLX](/wiki/ASPIDA_DLX "ASPIDA DLX") core. Another was offered by [ARM Holdings](/wiki/ARM_Holdings "ARM Holdings"). They do not, however, have any speed advantages because modern computer designs already run at the speed of their slowest component, usually memory. They do use somewhat less power because a clock distribution network is not needed. An unexpected advantage is that asynchronous computers do not produce spectrally\-pure radio noise. They are used in some radio\-sensitive mobile\-phone base\-station controllers. They may be more secure in cryptographic applications because their electrical and radio emissions can be more difficult to decode.


How do bits from a microprogram control other parts of a computer?