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| Computer architecture bit widths |
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Incomputer architecture,12-bitintegers,memory addresses, or otherdata units are those that are 12bits (1.5 octets) wide. Also, 12-bitcentral processing unit (CPU) andarithmetic logic unit (ALU) architectures are those that are based onregisters,address buses, ordata buses of that size.
Before the widespread adoption ofASCII in the late 1960s,six-bit character codes were common and a 12-bit word, which could hold two characters, was a convenient size. This also made it useful for storing a single decimal digit along with a sign. Possibly the best-known 12-bit CPUs are thePDP-8 and its descendants (such as theIntersil 6100 microprocessor), which were produced in various forms from August 1963 to mid-1990. Manyanalog to digital converters (ADCs) have a 12-bit resolution. SomePIC microcontrollers use a 12-bit instruction word but handle only 8-bit data.
12 binary digits, or 3 nibbles (a 'tribble'), have 4096 (10000octal, 1000hexadecimal) distinct combinations. Hence, a microprocessor with 12-bit memory addresses can directly access 4096words (4 kW) ofword-addressable memory. IBMSystem/360 instruction formats use a 12-bit displacement field which, added to the contents of a base register, can address 4096 bytes of memory in a region that begins at the address in the base register.
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