The Alpha

Also designed by Digital, the Alpha, otherwise known as the AXP, is a 64-bit RISC design, the world's first 64-bit architecture. (Source: "VAX & OpenVMS at 20," Digital Equipment Corp., 1997.)

Since its debut in 1992, the Alpha architecture has set many performance records, and except for a few brief periods when competing products have temporarily leapfrogged it, the Alpha has outperformed all of its competitors.

As a RISC architecture, the Alpha faced a challenge in supplying the kinds of services that the OpenVMS operating system relied on in the VAX. Long, complex instructions were out of the question, exactly the kind that OpenVMS depended on heavily. To solve this challenge, the designers put together a system called "PALcode," short for "privileged architecture library." This system breaks down the complex instructions into sequences of small RISC instructions and allows the operating system to execute them almost as if they were single instructions. This system is adaptable to allow several different operating systems to run on the Alpha, including UNIX and Windows NT. Windows 2000 was also partially developed on Alpha machines, although there was never a production version of Windows 2000 for Alpha.

Throughout the early and mid-1990s, OpenVMS was developed in parallel on VAX and Alpha machines, with new features appearing first on VAX, then being added later to the Alpha version. As time went on, however, this relationship was reversed, with new features appearing first on Alpha. As of today, some features of OpenVMS are available only on Alpha, particularly those having to do with 64-bit addressing and support for a new file system structure.