Page "DEC Alpha" Paragraph 8

Alpha was born out of an earlier RISC project named PRISM, itself the final product of several earlier projects.

PRISM was intended to be a flexible design, supporting both Unix-like applications, as well as Digital's existing VMS programs from the VAX after minor conversion.

In order to support the VAX architecture with reasonable performance, PRISM included a user-programmable microcode known as Epicode.

Using Epicode, key portions of the VAX instruction set could be directly encoded into the PRISM, greatly improving performance.

A new Unix-like operating system known as Mica would run applications natively, supporting VMS under emulation running at the same time.