The '''National IMP-4''' is a [[microprocessor family|family]] of multi-chip [[4-bit architecture|4-bit]] [[bit-slice microprocessor|bit-slice]] [[microprocessor]] developed by [[National Semiconductor]] and introduced in 1974. Units could be combined to implement systems with 4 to 32-bit words. The {{national|IMP-8}} and {{national|IMP-16}} families were made using the IMP-4 logic. The IMP-4 had 2 chips: a {{national|IMP-4A/521|control unit}} and an ALU, some systems used the {{national|IMP-00A/520|RALU}} with custom control circuitry. The {{national|IMP-00A/520|RALU}} was the first [[bit-slice microprocessor|bit-slice]] microprocessor - predating both the {{intel|3000}} and the {{amd|am2900}}.