The Alpha 21164, also known by its code name, EV5, is a microprocessor developed and fabricated by Digital Equipment Corporation that implemented the Alpha instruction set architecture (ISA). It was introduced in January 1995, succeeding the Alpha 21064A as Digital's flagship microprocessor. It was succeeded by the Alpha 21264 in 1998.

The Alpha 21164 was introduced in January 1995 at 266 MHz. A 300 MHz version was introduced in March 1995. The final Alpha 21164, a 333 MHz version, was announced on 2 October 1995, available in sample quantities. The Alpha 21164 was replaced by the Alpha 21164A as Digital's flagship microprocessor in 1996 when a 400 MHz version became available in volume quantities. The Alpha 21164 was the basis of a further development code-named EV56. It was introduced as the Alpha 21164, but was originally known as the Alpha 21164A. It operated at clock frequencies of 366, 433, 500, 533, 600 and 666 MHz.

This example in our collection has not been marked with a part number or a speed grade, it might be a manufacturing reject, but the pencil markings suggest that it is a validation test sample. The date code is from the time when parts were shipping at 400MHz, so it is possible that this is a test sample of the 433 MHz part, which would have the part number 21164-HB 433.