DEC Alpha

Alpha, originally known as Alpha AXP, is a 64-bit reduced instruction set computing (RISC) instruction set architecture (ISA) developed by Digital Equipment Corporation (DEC), designed to replace their 32-bit VAX complex instruction set computer (CISC) ISA. Alpha was implemented in microprocessors originally developed and fabricated by DEC. These microprocessors were most prominently used in a variety of DEC workstations and servers, which eventually formed the basis for almost all of their mid-to-upper-scale lineup. Several third-party vendors also produced Alpha systems, including PC form factor motherboards. Alpha, originally known as Alpha AXP, is a 64-bit reduced instruction set computing (RISC) instruction set architecture (ISA) developed by Digital Equipment Corporation (DEC), designed to replace their 32-bit VAX complex instruction set computer (CISC) ISA. Alpha was implemented in microprocessors originally developed and fabricated by DEC. These microprocessors were most prominently used in a variety of DEC workstations and servers, which eventually formed the basis for almost all of their mid-to-upper-scale lineup. Several third-party vendors also produced Alpha systems, including PC form factor motherboards. Operating systems that supported Alpha included OpenVMS (previously known as OpenVMS AXP), Tru64 UNIX (previously known as DEC OSF/1 AXP and Digital UNIX), Windows NT (discontinued after NT 4.0; and pre-release Windows 2000 RC1), Linux (Debian, SUSE, Gentoo and Red Hat), BSD UNIX (NetBSD, OpenBSD and FreeBSD up to 6.x), Plan 9 from Bell Labs, as well as the L4Ka::Pistachio kernel. The Alpha architecture was sold, along with most parts of DEC, to Compaq in 1998. Compaq, already an Intel customer, phased out Alpha in favor of the forthcoming Hewlett-Packard/Intel Itanium architecture, and sold all Alpha intellectual property to Intel in 2001, effectively killing the product. Hewlett-Packard purchased Compaq later that same year, continuing development of the existing product line until 2004, and selling Alpha-based systems, largely to the existing customer base, until April 2007. Alpha was born out of an earlier RISC project named Prism (Parallel Reduced Instruction Set Machine), itself the 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. A new Unix-like operating system known as Mica would run applications natively, supporting VMS under emulation running at the same time. During development, the Palo Alto design team were working on a Unix-only workstation that originally included the PRISM. However, development of the workstation was well ahead of the PRISM, and the engineers proposed that they release the machines using the MIPS R2000 processor instead, moving its release date up considerably. DEC management doubted the need to produce a new computer architecture to replace their existing VAX and DECstation lines, and eventually ended the PRISM project in 1988. By the time of cancellation, however, second-generation RISC chips (such as the newer SPARC architecture) were offering much better price/performance ratios than the VAX lineup. It was clear a third generation would completely outperform the VAX in all ways, not just on cost. Another study was started to see if a new RISC architecture could be defined that could directly support the VMS operating system. The new design used most of the basic PRISM concepts, but was re-tuned to allow VMS and VMS programs to run at reasonable speed with no conversion at all. The decision was also made to upgrade the design to a full 64-bit implementation from PRISM's 32-bit, a conversion all of the major RISC vendors were undertaking. Eventually that new architecture became Alpha. The primary Alpha instruction set architects were Richard L. Sites and Richard T. Witek. The PRISM's Epicode was developed into the Alpha's PALcode, providing an abstracted interface to platform- and processor implementation-specific features. The main contribution of Alpha to the microprocessor industry, and the main reason for its performance, was not so much the architecture but rather its implementation. At that time (as it is now), the microchip industry was dominated by automated design and layout tools. The chip designers at Digital continued pursuing sophisticated manual circuit design in order to deal with the overly complex VAX architecture. The Alpha chips showed that manual circuit design applied to a simpler, cleaner architecture allowed for much higher operating frequencies than those that were possible with the more automated design systems. These chips caused a renaissance of custom circuit design within the microprocessor design community. Originally, the Alpha processors were designated the DECchip 21x64 series, with 'DECchip' replaced in the mid-1990s with 'Alpha'. The first two digits, '21' signifies the 21st century, and the last two digits, '64' signifies 64 bits. The Alpha was designed as 64-bit from the start and there is no 32-bit version. The middle digit corresponded to the generation of the Alpha architecture. Internally, Alpha processors were also identified by EV numbers, EV officially standing for 'Extended VAX' but having an alternative humorous meaning of 'Electric Vlasic', giving homage to the Electric Pickle experiment at Western Research Lab.