4-bit computing: Difference between revisions

Revision as of 02:44, 16 November 2023

Revision as of 13:50, 17 November 2023

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{{Computer architecture bit widths}}

'''4-bit computing''' is the use of [[computer architecture]]s in which [[integer (computer science)|integers]] and other [[data (computer science)|data]] units are 4 [[bit]]s wide. 4-bit [[central processing unit]] (CPU) and [[arithmetic logic unit]] (ALU) architectures are those that are based on [[processor register|registers]] or [[Bus (computing)|data buses]] of that size. [[MemoryA address]]esgroup (andof thusfour [[addressbits bus]]es)is foralso 4-bitcalled CPUsa are[[nibble]] generallyand much larger thanhas 2^4-bit (since only= 16 memory locations would be very restrictive), such as 12-bit or more, while they could in theory bepossible 8-bitvalues.

4-bit processors were widely used in [[electronic calculator]]s and other roles where decimal math was used, like electronic [[cash register]]s, [[microwave oven]] timers, and so forth. This is because a 4-bit value holds a single [[binary coded decimal]] (BCD) digit, making it a natural size for directly processing decimal values. As a 4-bit value is generally too small to hold a [[memory address]] for real-world programs or data, the [[address bus]] of these systems was generally larger. For instance, the canonical 4-bit [[microprocessor]], the [[Intel 4004]], had a 12-bit address format.

A group of four bits is also called a [[nibble]] and has 2⁴ = 16 possible values.

4-bit designs were used only for a short period when [[integrated circuit]]s were still expensive, and were found primarily in cost-sensitive roles. While 4-bit computing is mostly obsolete, 4-bit values are still used in the same decimal-centric roles they were developed for, and modern implementations are generally much wider and process multiple 4-bit values in parallel. An example of such a system is the [[HP Saturn]] design of the 1980s. By the 1990s, most such uses had been replaced by general purpose binary designs.

While 4-bit computing is mostly obsolete, 4-bit communication (even 1- or 2-bit) is still used in modern computers, that are otherwise e.g. 64-bit, and thus also have much larger buses.

== History ==