DEC Alpha
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The DEC Alpha, also known as the Alpha AXP, is a 64-bit RISC microprocessor originally developed and fabricated by Digital Equipment Corp (DEC). Designed to power successors to the VAX line of computers, it was used in a variety of DEC workstations and servers, eventually forming the basis for almost all of their entire mid-to-upper-scale lineup. Several third-party vendors also produced Alpha systems, as well as PC compatible form factor motherboards.
Alpha supports both the OpenVMS operating system and Tru64 UNIX (previously known as DEC OSF/1 AXP or Digital UNIX). Open source operating systems also run on the Alpha, notably Linux and BSD UNIX flavors. Microsoft supported the processor in Windows NT until NT 4.0 SP6 but did not extend Alpha support beyond RC1 of Windows 2000[1].
The Alpha series was sold, along with most parts of DEC, to Compaq in 1998. Compaq, already an Intel customer, decided to phase out Alpha in favor of the forthcoming Intel IA-64 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 promising to continue selling Alpha-based systems, largely to the existing customer base, until October 2006.
In November 2006, HP announced an extension to sales until 27th April 2007.
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[edit] History
Alpha was born out of an earlier RISC project named PRISM, itself the final product of several earlier projects. DEC had been marketing the DECstation line of workstations based on the MIPS architecture, and unsurprisingly PRISM shared many features with MIPS. Among the differences between PRISM and MIPS, however, was that PRISM supported a user-programmable microcode known as Epicode. 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 doubted the need to produce a new computer architecture to replace their existing VAX and DECstation lines, and eventually killed 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 Alpha instruction set architects were Dick Sites and Rich 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 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 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.
Officially, the Alpha processors were designated the DECchip 21x64 series, the "21" signifying the 21st century, and the "64" indicating 64 bits, with the middle digit corresponding 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"[1].
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. The 21364 or EV7 was the first processor to include an integrated memory controller. The unproduced EV8 would have been the first to include simultaneous multithreading, but this version was caught up in the sale to Compaq. The Tarantula research project, which most likely would have been called EV9, would have been the first processor to feature a powerful vector core.
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".
[edit] Versions
At the time of its announcement, Alpha was heralded as an architecture for the next 25 years. While this was not to be, Alpha has nevertheless had a reasonably long life. The first version, the Alpha 21064 (otherwise known as the EV4) was introduced in 1992 running at up to 192 MHz, a slight (0.75μm to 0.675μm) shrink of the die (EV4S) ran at 200 MHz a few months later. 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 circuit design, a hallmark of the Hudson design team, like a huge centralized clock circuitry, allowed them to run the CPU at higher speeds, even though the microarchitecture was fairly similar to other RISC chips. In comparison, the less expensive Intel Pentium ran at 66 MHz when it was launched the following spring.
The Alpha 21164 or EV5 became available in 1995 at processor frequencies of up to 333 MHz. In July 1996 the line was speed bumped to 500 MHz, in March 1998 to 666 MHz. Also in 1998 the 21264 (EV6) was released at 450 MHz, eventually reaching (in 2001 with the 21264C/EV68CB) 1.25 GHz. In 2003, the EV7 Marvel was launched, essentially an EV68 core with four 1.6 Gbyte/s inter-processor communication links for improved multiprocessor system performance, running at 1 or 1.15 GHz. Around 500,000 Alpha based systems were sold by the end of 2000.
In 1999, 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.
On June 25, 2001, Compaq announced that Alpha would be phased out by 2004 in favor of Intel's Itanium, canceled the planned EV8 chip, and sold all Alpha intellectual property to Intel. HP, new owner of Compaq later the same year, announced that development of the Alpha series would continue for a few more years, including the release of a 1.3 GHz EV7 variant called the EV7z. This would be the final iteration of Alpha, the 0.13µm EV79 also being canceled. HP will continue selling AlphaServers with OpenVMS and Tru64 UNIX until April 27, 2007, and has promised support until at least 2012.
Ironically, in mid-2003, as the Alpha was about to be phased out, the fastest and second fastest computers (in 2002) in the United States were both implemented using Alpha processors (in the case of the former, a cluster of 4096 Alpha processors).
[edit] Model history
| Model | Model number | Year | Frequency [MHz] | Process [µm] | Transistors [millions] | Die size [mm²] | IO Pins | Power [W] | Voltage | Mem [MB/s] | Dcache [KB] | Icache [KB] | Scache | Bcache | ISA |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| EV4 | 21064 | 1992 | 100–200 | 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 | -- | |||
| LCA4 | 21068 | 1994 | 66 | 0.68 | 1.75 | 209 | 9 | 3.3 | 30 | 8 | 8 | -- | |||
| LCA45 | 21066A | 1994 | 166–233 | 0.5 | 1.75 | 161 | 23 | 3.3 | 30 | 8 | 8 | -- | |||
| LCA45 | 21068A | 1994 | 100 | 0.5 | 1.75 | 161 | 3.3 | 30 | 8 | 8 | -- | ||||
| EV5 | 21164 | 1995 | 266–500 | 0.5 | 9.7 | 299 | 296 | 56 | 3.3/2.5 | 150 | 8 | 8 | 96 KB | 1 | R |
| EV56 | 21164A | 1996 | 400–767 | 0.35 | 9.3 | 209 | 46 | 3.3/2.0 | 300 | 8 | 8 | 96 KB | 1–2 MB | R,B | |
| PCA56 | 21164PC | 1997 | 400–533 | 0.35 | 3.5 | 141 | 264 | 40 | 3.3/2.5 | 8 | 16 | -- | 1 MB | R,B,M | |
| PCA57 | 21164PC | 600–666 | 0.28 | 5.7 | 101 | 283 | 20 | 2.5/2.0 | 16 | 16 | -- | 1 MB | R,B,M | ||
| EV6 | 21264 | 1998 | 450–600 | 0.35 | 15.2 | 314 | 389 | 73 | 2.0 | 1600 | 64 | 64 | -- | 2–8 MB | R,B,M,F |
| EV67 | 21264A | 1999 | 667–750 | 0.25 | 15.2 | 210 | 389 | 2.0 | 64 | 64 | -- | 2–8 MB | R,B,M,F,C | ||
| EV68AL | 21264B | 2001 | 800–833 | 0.18 | 15.2 | 125 | 1.7 | 64 | 64 | -- | 2–8 MB | R,B,M,F,C,T | |||
| EV68CB | 21264C | 2001 | 1000–1250 | 0.18 | 15.2 | 125 | 65–75 | 1.65 | 64 | 64 | -- | 2–8 MB | R,B,M,F,C,T | ||
| EV68CX | 21264D | 1.65 | 64 | 64 | -- | 2–8 MB | R,B,M,F,C,T | ||||||||
| EV7/EV7z | 21364 | 2003 | 800–1300 | 0.18 | 130 | 397 | 1443 | 125 | 1.5 | 64 | 64 | 1.75 MB | -- | R,B,M,F,C,T | |
| EV79 | 21364A(?) | (canceled) | 1700 | 0.13 | 152 | 300 | 1443 | 120 | 1.2 | 64 | 64 | 1.75 MB? | -- | R,B,M,F,C,T | |
| EV8 | 21464 | (canceled — was to be 2003) | 2800 | 0.13 | 250 | 350? | 1800 | ?? | ?? | ?? | 64 | 64 | 3–4 MB? | -- | R,B,M,F,C,T |
| 21466 | (canceled — was to be 2003) | 3300 | 0.13 | 250 | 350? | 1800 | ?? | ?? | ?? | 64 | 64 | 3–4 MB? | -- | R,B,M,F,C,T |
ISA extensions:
- R: ?
- B: BWX, the "Byte/Word Extension", adding instructions to allow 8- and 16-bit operations from memory and I/O
- M: MVI, "multimedia" instructions
- F: FIX, instructions to move data between integer and floating point registers and for square root
- C: CIX, instructions for counting and finding bits
- T: Support for prefetch with modify intent to improve the performance of the first attempt to acquire a lock
[edit] Performance
To get an idea of the performance of Alpha-based systems, here are some SPEC performance numbers (SPEC92, SPEC95). Note that the SPEC results report the measured performance of a whole computer system (CPU, bus, memory, compiler optimizer), not just the CPU. Also note that the benchmark and scale changed from 1992 to 1995. However, the idea here is to give a rough idea of the Alpha architecture performance compared with Intel-based offerings at the same time. Perhaps the most obvious trend is that while Intel could always get reasonably close to Alpha in integer performance, in floating point performance the difference was considerable.
| System | CPU | MHz | Year | integer | floating point |
|---|---|---|---|---|---|
| AlphaServer 8400 5/350 | 21164 (EV5) | 350 | 1995 | int92 432.8 | fp92 602.2 |
| Adler | Pentium Pro | 200 | 1995 | int92 366.0 | fp92 283.2 |
| AlphaServer ES40 6/833 | 21264 (EV6) | 833 | 2000 | int95 50.0 | fp95 100.0 |
| Intel VC820 motherboard | Pentium III | 1000 | 2000 | int95 46.8 | fp95 31.9 |
[edit] Alpha-based systems
The first generation of DEC Alpha-based systems comprised the DEC 3000 AXP series workstations and low-end servers, DEC 4000 AXP series mid-range servers, and DEC 7000 AXP and 10000 AXP series high-end servers. The DEC 3000 AXP systems used the same TURBOchannel bus as the previous MIPS-based DECstation models, whereas the 4000 was based on FutureBus+ and the 7000/10000 shared an architecture with corresponding VAX models.
DEC also produced a PC-like Alpha workstation with an EISA bus, the DECpc 150 AXP (codename "Jensen", also known as the DEC 2000 AXP). This was the first Alpha system to support Windows NT. DEC later produced Alpha versions of their Celebris XL and Personal Workstation PC lines, with 21164 processors.
The 21066 chip was used in the DEC Multia VX40/41/42 compact workstation and the ALPHAbook 1 laptop from Tadpole Technology.
In 1994, DEC launched a new range of AlphaStation and AlphaServer systems. These used 21064 or 21164 processors and introduced the PCI bus, VGA-compatible frame buffers and PS/2-style keyboards and mice. The AlphaServer 8000 series superseded the DEC 7000/10000 AXP and also employed XMI and FutureBus+ buses.
The AlphaStation XP1000 was the first workstation based on the 21264 processor. Later AlphaServer/Station models based on the 21264 were categorised into DS (departmental server), ES (enterprise server) or GS (global server) families.
The final 21364 chip was used in the AlphaServer ES47, ES80 and GS1280 models.
A number of OEM Alpha motherboards were also produced by DEC, Samsung and API, including the EB64+, EB164, API UP1000 and UP2000.
The 21164 and 21264 processors were used by Network Appliance in various Network Attached Storage systems, while the 21064 and 21164 processors were used by Cray in their T3D and T3E massively parallel supercomputers.
[edit] Supercomputers
The fastest supercomputers based on Alpha processors:
- ASCI Q at Los Alamos National Laboratory. Machine: HP AlphaServer SC45/GS Cluster. CPU: 4096 Alpha (1.25 GHz). Rmax: 7.727 Teraflops.
Cray Research used the 21064 and 21164 processors respectively in the Cray T3D and Cray T3E massively parallel supercomputers.
[edit] References
- ^ Aaron Sakovich (2001). Windows 2000?. The AlphaNT Source. Retrieved on 2007-01-01.
[edit] External links
- Documents from Digital
- Digital Technical Journal, Volume 4, Number 4, Special Issue 1992 Alpha AXP Architecture and Systems This issue contains several articles from Alpha's Architects
- DEC Alpha Documentation Library Technical documentation for Alpha microprocessors and motherboards, last updated in 1999 (includes the Alpha Architecture Handbook)
- DEC Alpha Documentation Archives Technical documentation for older Alpha products
- AlphaServer News Sites
- Tru64.org Tru64 UNIX on Alpha
- OpenVMS.org OpenVMS on Alpha
- Free Operating Systems for Alpha
- Plan 9 on Alpha
- L4Ka::Pistachio/alpha
- Alpha Core - Fedora Core for Alpha
- CentOS Linux on Alpha
- Gentoo Linux on Alpha
- Debian on Alpha
- NetBSD/alpha
- OpenBSD/alpha
- FreeBSD/alpha
- Other Sources
| RISC |
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| Power Architecture · ARM architecture · DEC Alpha · Atmel AVR · MIPS architecture · PA-RISC · Parallax Propeller · PIC microcontroller · SPARC · SuperH · XAP processor · I960 · Motorola 88000 |
