DEC 21064 / 21064A

21064 is a 64-bit superscalar microprocessor developed by Digital Equipment Corporation (DEC) in 1990s, and based on Alpha AXP architecture. The Alpha architecture was announced in February 1992, and the first 21064 processors, running at frequencies 150 MHz and higher, were launched at COMDEX show in November 1992. Initially Alpha chips were built on 0.75 micron CMOS technology, and later the technological process was upgraded to 0.675 micron. Internally, 21064 is a RISC design with load/store architecture, 32-bit fixed instruction size, 32 integer and 32 FP 64-bit registers, and separate integer and floating-point pipelines. The CPU incorporates a number of features, used to improve overall performance: on-chip 8 KB instruction and 8 KB data level 1 caches, branch prediction, ability to utilize 128-bit data bus, and others. The 21064 CPUs were manufactured in a big, compared to other CPUs of its time, and distinctive looking ceramic 431-pin PGA package with integrated heatspreader.

In October 1993, Digital Equipment Corporation announced updated version of the 21064. New 21064A microprocessors, also known as EV45, were built on 0.5 micron process, had clock speeds from 200 MHz and up to 300 MHz, and featured larger 16 KB instruction and 16 KB data L1 caches. The 21064A CPUs were packaged in the same type of package as the 21064.