![]() ![]() "MARC4 Family of 4 bit Forth CPU" (which is now discontinued) because of the extreme size constraint on programs and because common programming languages (for microcontrollers, 8-bit and larger), such as the C programming language, do not support 4-bit data types (C, and C++, and more languages require that the size of the char data type be at least 8 bits, and that all data types other than bitfields have a size that is a multiple of the character size ). ![]() The 4-bit processors were programmed in assembly language or Forth, e.g. It was steadily improved and by 1975 been combined with several support chips to make a one-chip computer. The Rockwell PPS-4 was another early 4-bit processor, introduced in 1972, which had a long lifetime in handheld games and similar roles. The Texas Instruments TMS 1000 (1974) was a 4-bit CPU it had a Harvard architecture, with an on-chip instruction ROM, 8-bit-wide instructions and an on-chip data RAM with 4-bit words. The first commercial microprocessor was the binary-coded decimal (BCD-based) Intel 4004, developed for calculator applications in 1971 it had a 4-bit word length, but had 8-bit instructions and 12-bit addresses. See also: Bit slicing#Bit-sliced quantum computers. ![]() Traditional (non-quantum) 4-bit computers are by now obsolete, while recent quantum computers are 4-bit, but also based on qubits, such as the IBM Q Experience. Some of the first microprocessors had a 4-bit word length and were developed around 1970. A group of four bits is also called a nibble and has 2 4 = 16 possible values. Memory addresses (and thus address buses) for 4-bit CPUs are generally much larger than 4-bit (since only 16 memory locations would be very restrictive), such as 12-bit or more, while they could in theory be 8-bit. Also, 4-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers, or data buses of that size. In computer architecture, 4-bit integers, or other data units are those that are 4 bits wide. ![]()
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