The IMP-16, by

National Semiconductor National Semiconductor was an American semiconductor manufacturer which specialized in analog devices and subsystems, formerly with headquarters in Santa Clara, California. The company produced power management integrated circuits, display dr ...

, was the first multi-chip

16-bit 16-bit microcomputers are microcomputers that use 16-bit microprocessors. A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two ...

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circ ...

, released in 1973. It consisted of five PMOS

integrated circuits An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tin ...

: four identical RALU chips, short for

register Register or registration may refer to: Arts entertainment, and media Music * Register (music), the relative "height" or range of a note, melody, part, instrument, etc. * ''Register'', a 2017 album by Travis Miller * Registration (organ), th ...

and ALU, providing the data path, and one CROM, Control and ROM, providing control sequencing and

microcode In processor design, microcode (μcode) is a technique that interposes a layer of computer organization between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. Microcode is a la ...

storage. The IMP-16 is a bit-slice processor; each RALU chip provides a

4-bit In computer architecture, 4-bit integers, or other data units are those that are 4 bits wide. 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 si ...

slice of the register and arithmetic that work in parallel to produce a 16-bit word length. Each RALU chip stores its own 4 bits of the program counter, several registers, the ALU, a 16-word LIFO stack, and status flags. There were four 16-bit accumulators, two of which could be used as index registers. The

instruction set architecture In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...

was similar to that of the

Data General Nova The Data General Nova is a series of 16-bit minicomputers released by the American company Data General. The Nova family was very popular in the 1970s and ultimately sold tens of thousands of units. The first model, known simply as "Nova", was ...

. The chip set could be extended with the CROM chip (IMP-16A / 522D) that implemented 16-bit multiply and divide routines. The chipset was driven by a two-phase 715 kHz non-overlapping clock that had a +5 to -12 voltage swing. An integral part of the architecture was a 16-bit input mux that provided various condition bits from the ALUs such as zero, carry, overflow along with general purpose inputs. The microprocessor was used in the IMP-16P microcomputer and Jacquard Systems' J100 but saw little other use. The IMP-16 was later superseded by the

PACE Pace or paces may refer to: Business *Pace (transit), a bus operator in the suburbs of Chicago, US *Pace Airlines, an American charter airline * Pace Foods, a maker of a popular brand of salsa sold in North America, owned by Campbell Soup Compan ...

and INS8900 single-chip 16-bit microprocessors, which had a similar architecture but were not binary compatible.

References

{{reflist

External links

IMP-16C board at the Selectric Typewriter Museum
IMP-16 16-bit microprocessors Computers using bit-slice designs