The DEC Alpha, also known as the Alpha AXP, is a 64-bit RISC microprocessor originally developed and fabricated by Digital Equipment Corp. (DEC), which used it in its own line of workstations and servers. Designed as a successor to the VAX line of computers, it supported the VMS operating system, as well as the DEC flavour of UNIX. Later open source operating systems also ran on the Alpha, notably Linux and certain BSD UNIX flavours. Microsoft supported the processor until Windows NT 4.0 SP6 and did not extend Alpha support to Windows 2000.
History
Alpha was born out of an earlier failed RISC project named PRISM. At the time, DEC had been working with the MIPS chipset for workstation designs, and unsurprisingly PRISM shared many features with the MIPS. PRISM had been designed with the intent of releasing a new operating system along with it, known as Emerald, which would allow it to run "native" programs at full speed while also supporting Digital's existing VMS programs from the VAX after minor conversion. DEC management never understood why they needed a new machine to replace their existing cash cow, and eventually killed the project in 1988.
By the time of cancellation, however, second generation RISC chips like the newer SPARC and MIPS, 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 first few generations of the Alpha chips were some of the most innovative of their time. The first version, 21064 or EV4, was the first CMOS microprocessor whose operating frequency rivalled higher-powered ECL minicomputers and mainframes. The second, 21164 or EV5, was the first microprocessor to place a large secondary cache on chip. The third, 21264 or EV6, was the first microprocessor to combine both high operating frequency and the more complicated out-of-order execution microarchitecture.
But the main contribution of Alpha to the microprocessor industry, and the main reason for its excellent performance, was not so much the architecture but rather superb implementation. At that time (as it is now), the microchip industry was dominated by automated logic synthesis driven design flows. The chip designers at Digital continued pursuing sophisticated circuit design in order to deal with the overly complex VAX architecture. The Alpha chips showed that custom (eg. human) circuit design styles when applied to a simpler, cleaner architecture allowed for much higher operating frequencies than those that were possible with the more automated design flows. These chips caused a renaissance of custom circuit design within the microprocessor design community.
A persistent report attributed to DEC insiders suggests the choice of the AXP tag for the processor was made by DEC's legal department, which was still smarting from the VAX trademark fiasco. After a lengthy search the tag "AXP" was found to be entirely unencumbered. Within the computer industry, a joke got started that the acronym AXP meant "Almost Exactly PRISM".
Versions
The first version, the Alpha 21064 was introduced in 1992 running at 200MHz. The 64-bit processor was a superpipelined and superscalar design, like other RISC designs, but nevertheless outperformed them all and DEC touted it as the world's fastest processor. Careful attention to process, a hallmark of the Hudson fab, allowed them to run the CPU at higher speeds, even though the design was fairly similar to other RISC chips. In comparison, the Intel Pentium ran at 66MHz when it was launched the following spring.
In July 1996 the 21164PC speed bumped the design to 500MHz, in March 1998 to 666MHz, and in May 2000 the 21264 was released at 731MHz (the 21264). 1GHz and faster pieces were announced in 2001 (the 21364 or EV7), and are available since 2003 at 1.1GHz+. Around 500,000 Alpha based systems were sold to end-2000.
The production of Alpha chips was licensed to Samsung Electronics Company. Following the purchase of Digital by Compaq the majority of the Alpha products were placed with API NetWorks, Inc. (previously Alpha Processor Inc.), a private company funded by Samsung and Compaq. In October 2001 Microway became the exclusive sales and service provider of API NetWorks' Alpha-based product line.
Compaq announced that computers using Alpha would be phased out by 2004 in favour of Intel's Itanium. HP, new owner of Compaq, announced that support for the Alpha series would continue for a few more years, including the release of the EV7z chip, but that this will be the final iteration of the chip. The IA-64 is supposed to replace this series.
Ironically, in mid-2003, as the Alpha was about to be phased out, the fastest computer in the U.S. (and second fastest in the world) was a cluster of 4096 Alpha processors.
On August 16, 2004 HP announced that they are releasing the 1.3GHz EV7z, and that it is to be the last Alpha model that they are going to produce.
Model History
| Model | AKA | Year | Frequency [Mhz] | Process [µm] | Transistors [millions] | Die size [mm²] | IO Pins | Power [W] | Voltage | Mem [MB/s] | Dcache [k] | Icache [k] | Scache | Bcache | ISA |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| EV4 | 21064 | 1992 | 150-200 | 0.75 | 1.68 | 234 | 290 | 30 | 3.3 | 80 | 8 | 8 | -- | ||
| EV45 | 21064A | 1994 | 200-300 | 0.5 | 2.85 | 164 | 33 | 3.3 | 80 | 16 | 16 | -- | |||
| LCA4 | 21066 | 1993 | 100-166 | 0.68 | 1.75 | 209 | 21 | 3.3 | 30 | 8 | 8 | -- | |||
| LCA45 | 21066A | 1994 | 166-233 | 0.5 | 1.75 | 161 | 23 | 3.3 | 30 | 8 | 8 | -- | |||
| EV5 | 21164 | 1995 | 366-500 | 0.5 | 9.7 | 299 | 296 | 56 | 3.3/2.5 | 150 | 8 | 8 | 96k | 1 | R |
| EV56 | 21164A | 1996 | 400-767 | 0.35 | 9.3 | 209 | 46 | 3.3/2.0 | 300 | 8 | 8 | 96k | 1-2M | R,B | |
| PCA56 | 21164PC | 1997 | 400-533 | 0.35 | 3.5 | 141 | 264 | 40 | 3.3/2.5 | 8 | 16 | -- | 1M | R,B,M | |
| PCA57 | 600-666 | 0.28 | 5.7 | 101 | 283 | 20 | 2.5/2.0 | 16 | 16 | -- | 1M | R,B,M | |||
| EV6 | 21264 | 1998 | 450-600 | 0.35 | 15.9 | 314 | 389 | 73 | 2.0 | 1600 | 64 | 64 | -- | 2-8M | R,B,M,F |
| EV67 | 21264A | 1999 | 667-750 | 0.25 | 15.9 | 210 | 389 | 64 | 64 | -- | 2-8M | R,B,M,F,C | |||
| EV68AL | 21264B | 2001 | 800-833 | 0.18 | 15.9 | 125 | 64 | 64 | -- | 2-8M | R,B,M,F,C,T | ||||
| EV68CB | 21264C | 64 | 64 | -- | 2-8M | R,B,M,F,C,T | |||||||||
| EV68CX | 21264D | 64 | 64 | -- | 2-8M | R,B,M,F,C,T | |||||||||
| EV7 | 21364 | 2003 | 800- | 0.18 | 64 | 64 | 1.75M | -- | R,B,M,F,C,T |