VAX

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DEC VAX
Manufacturer: Digital Equipment Corporation
Byte size: 8 bits (octet)
Address bus size: 32 bits
Peripheral bus: Unibus, Massbus, Q-Bus, XMI, VAXBI
Architecture: CISC, virtual memory
Operating systems: VAX/VMS, Ultrix, BSD UNIX, VAXELN
For the vacuum cleaner, see Vax (vacuum).

VAX is a 32-bit computing architecture that supports an orthogonal instruction set (machine language) and virtual addressing (i.e. demand paged virtual memory). It was developed in the mid-1970s by Digital Equipment Corporation (DEC). DEC was later purchased by Compaq, which in turn was purchased by Hewlett-Packard.

The VAX has been perceived as the quintessential CISC processing architecture, with its very large number of addressing modes and machine instructions, including instructions for such complex operations as queue insertion/deletion and polynomial evaluation.[citation needed]

Contents

[edit] Name

"VAX" was originally an acronym for Virtual Address eXtension, both because the VAX was seen as a 32-bit extension of the older 16-bit PDP-11 and because it was (after Prime Computer) an early adopter of virtual memory to manage this larger address space. Early versions of the VAX processor implemented a "compatibility mode" that emulated many of the PDP-11's instructions, and were in fact called VAX-11 to highlight this compatibility and the fact that VAX-11 was an outgrowth of the PDP-11 family. Later versions offloaded the compatibility mode and some of the less used CISC instructions to emulation in the operating system software. The plural form of VAX is usually VAXes, but VAXen is also heard.

[edit] Operating systems

The "native" VAX operating system is DEC's VAX/VMS (renamed to OpenVMS in 1991 or 1992 when it was ported to DEC Alpha, "branded" by the X/Open consortium, and modified to comply with POSIX standards[1][citation needed]). The VAX architecture and VMS operating system were "engineered concurrently" to take maximum advantage of each other, as was the initial implementation of the VAXcluster facility. Other VAX operating systems have included various releases of BSD UNIX up to 4.3BSD, Ultrix-32 and VAXELN. More recently, NetBSD and OpenBSD support various VAX models and some work has been done on porting Linux to the VAX architecture.

VAX-11/780
VAX-11/780

[edit] History

The first VAX model sold was the VAX-11/780, which was introduced on October 25, 1977 at the Digital Equipment Corporation's Annual Meeting of Shareholders[1]. The architect of this model was Bill Strecker. Many different models with different prices, performance levels, and capacities were subsequently created. VAX superminis were very popular in the early 1980s.

For a while the VAX-11/780 was used as a baseline in CPU benchmarks because its speed was about one MIPS. Ironically enough, though, the actual number of instructions executed in 1 second was about 500,000. One VAX MIPS was the speed of a VAX-11/780; a computer performing at 27 VAX MIPS would run the same program roughly 27 times as fast as the VAX-11/780. Within the Digital community the term VUP (VAX Unit of Performance) was the more common term, because MIPS do not compare well across different architectures. The related term cluster VUPs was informally used to describe the aggregate performance of a VAXcluster. The performance of the VAX-11/780 still serves as the baseline metric in the BRL-CAD Benchmark, a performance analysis suite included in the BRL-CAD solid modeling software distribution.

VAX 8350 front view with cover removed.
VAX 8350 front view with cover removed.

The VAX went through many different implementations. The original VAX was implemented in TTL and filled more than one rack for a single CPU. CPU implementations that consisted of multiple ECL gate array or macrocell array chips included the 8600, 8800 superminis and finally the 9000 mainframe class machines. CPU implementations that consisted of multiple MOSFET custom chips included the 8100 and 8200 class machines.

The MicroVAX I represented a major transition within the VAX family. At the time of its design, it was not yet possible to implement the full VAX architecture as a single VLSI chip (or even a few VLSI chips as was later done with the V-11 CPU of the VAX 8200/8300). Instead, the MicroVAX I was the first VAX implementation to move most of the complexity of the VAX instruction set into emulation software, preserving just the core instructions in hardware. This new partitioning substantially reduced the amount of microcode required and was referred to as the "MicroVAX" architecture. In the MicroVAX I, the ALU and registers were implemented as a single gate-array chip while the rest of the machine control was conventional logic.

A full VLSI (microprocessor) implementation of the MicroVAX architecture then arrived with the MicroVAX II's 78032 (or DC333) CPU and 78132 (DC335) FPU. The 78032 was the first microprocessor with an on-board memory management unit[2] The MicroVAX II was based on a single, quad-sized processor board which carried the processor chips and ran the MicroVMS or Ultrix-32 operating systems. The machine featured 1 MB of on-board memory and a Q22-bus interface with DMA transfers. The MicroVAX II was succeeded by many further MicroVAX models with much improved performance and memory.

Further VLSI VAX processors followed in the form of the V-11, CVAX, SOC ("System On Chip", a single-chip CVAX), Rigel, Mariah and NVAX implementations. The VAX microprocessors extended the architecture to inexpensive workstations and later also supplanted the high-end VAX models. This wide range of platforms (mainframe to workstation) using one architecture was unique in the computer industry at that time. Sundry graphics were etched onto the CVAX microprocessor die. The phrase CVAX... when you care enough to steal the very best was etched in broken Russian as a play on a Hallmark Cards slogan, intended as a message to Soviet engineers who were known to be both purloining DEC computers for military applications, along with reverse engineering their chip design.[3] [4]

The VAX architecture was eventually superseded by RISC technology. In 1989 DEC introduced a range of workstations based on processors from MIPS Technologies and running Ultrix. In 1992 DEC introduced their own RISC processor, the Alpha (originally named Alpha AXP), a high performance 64-bit architecture capable of running OpenVMS.

In August 2000, Compaq announced that the remaining VAX models would be discontinued by the end of the year[2]. By 2005 all manufacturing of VAX computers had ceased, but old systems remain in widespread use.

The SRI CHARON-VAX and SIMH software-based VAX emulators remain available.

[edit] Processor architecture

[edit] Virtual Memory Map

The VAX virtual memory is divided into four sections, each of which is one gigabyte (1 GiB) in size:

Section Address Range
P0 0x00000000 - 0x3fffffff
P1 0x40000000 - 0x7fffffff
S0 0x80000000 - 0xbfffffff
S1 0xc0000000 - 0xffffffff

For VMS, P0 was used for user process space, P1 for process stack, S0 for the operating system, and S1 was reserved.

[edit] Privilege Modes

The VAX has four privilege modes:

No. Mode VMS Usage Notes
0 Kernel OS Kernel Highest Privilege Level
1 Executive File System
2 Supervisor Shell (DCL)
3 User Normal Programs Lowest Privilege Level

[edit] Processor Status Register

CM TP MBZ FD IS cmod pmod MBZ IPL MBZ DV FU IV T N Z V C
31 30 29 27 26 25 23 21 20 15 7 6 5 4 3 2 1 0
Bits Meaning
31 PDP-11 compatibility mode
30 trace pending
29:28 MBZ (must be zero)
27 first part done (interrupted instruction)
26 interrupt stack
25:24 current privilege mode
23:22 previous privilege mode
21 MBZ (must be zero)
20:16 IPL (interrupt priority level)
15:8 MBZ (must be zero)
7 decimal overflow trap enable
6 floating-point underflow trap enable
5 integer overflow trap enable
4 trace
3 negative
2 zero
1 overflow
0 carry

[edit] VAX models

Listed in roughly chronological order. The codenames used during development within Digital Equipment Corporation are shown in italic. VAX systems can be broadly classified into those with non-VLSI processors and those with VLSI processors with the MicroVAX-I being a transitional design:

This list is incomplete; you can help by expanding it.

[edit] Non-VLSI VAXen

VAX 11/780
Star, TTL CPU, October 1977[5]
VAX 11/750
Comet, More-compact, lower-performance TTL gate array-based implementation, October 1980
VAX 11/751
ruggedized rack-mount 11/750
VAX 11/730
Nebula, Still-more-compact, still-lower-performance bit slice implementation, April 1982
VAX 11/782
Atlas, Dual-processor 11/780
VAX 11/784
VAXimus, Four 11/780 CPUs sharing a single MA780 memory unit. Very rare
VAX 11/785
Superstar, Faster 11/780, April 1984
VAX 11/787
dual processor 11/785
VAX 11/788
VISQ
VAX 11/725
LCN, Low-Cost Nebula
VAX 8600
Venus, aka 11/790 during development, ECL gate array CPU, October 1984
VAX 8650
Morningstar, aka 11/795 during development, a faster 8600, last model to use SBI backplane also used by VAX 11/78x models, last model to have PDP-11 compatibility mode. All subsequent 8000 series models use VAXBI instead of SBI
VAX 8x00
Gemini, Fall-back in case the LSI-based Scorpio failed (never shipped)
VAX 8500
Flounder, Single-processor, deliberately-slowed VAX 8700
VAX 8530
Skipjack, Single-processor, less-slowed VAX 8700
VAX 8550
Skipjack, Single-processor 8800, unexpandable
VAX 8700
Nautilus, Single-processor Nautilus, expandable to full 8800
VAX 8800
Nautilus, Dual-processor ECL Macrocell array-based implementation, January 1986. Later also known as VAX 8820N
VAX 8810/8820/8830/8840
Polarstar, a Nautilus variant with one to four processors and an updated console processor
VAX 8974/8978
cluster comprising four or eight VAX 8810s respectively, January 1987
VAX 9000
Aridus, Air-cooled. Originally designed to be water-cooled, named Aquarius, ECL macrocell array CPU, VAXBI, October 1989[6]
VAX 9000 Model 110
VAX 9000 Model 210
VAX 9000 Model 310
VAX 9000 Model 4x0
x = number of processors, 1–4

[edit] A transitional VAX

MicroVAX/VAXstation I
Seahorse, KD32 CPU, October 1984

[edit] VLSI VAXen

MicroVAX series
some models also sold as VAXservers
MicroVAX II
Mayflower, KA630 CPU, May 1985
Industrial VAX 630
MicroVAX II in BA213 enclosure
MicroVAX III
BA23- or BA123-enclosure MicroVAX upgraded with KA650 CVAX CPU
MicroVAX III+
BA23- or BA123-enclosure MicroVAX upgraded with KA655 CPU
VAX 4
BA23- or BA123-enclosure MicroVAX upgraded with KA660 CPU
MicroVAX 2000
TeamMate, desktop form factor, February 1987
MicroVAX 3100 series
desktop form-factor, 1987 onwards
MicroVAX 3100 Model 10
TeamMate II, KA41-A CVAX processor
MicroVAX 3100 Model 10e
TeamMate II, KA41-D CVAX+ processor
MicroVAX 3100 Model 20
Model 10 in larger enclosure
MicroVAX 3100 Model 20e
Model 20 in larger enclosure
MicroVAX 3100 Model 30
Waverley/S, KA45 SOC CPU
MicroVAX 3100 Model 40
Model 30 in larger enclosure
MicroVAX 3100 Model 80
Waverley/M, KA47 Mariah CPU
MicroVAX 3100 Model 85
Waverley/M+, KA55 NVAX CPU
MicroVAX 3100 Model 88
Waverley/M+, KA58 NVAX CPU
MicroVAX 3100 Model 90
Cheetah, KA50 NVAX CPU
MicroVAX 3100 Model 95
Cheetah+, KA51 NVAX CPU
MicroVAX 3100 Model 96
Cheetah++, KA56 NVAX CPU
MicroVAX 3100 Model 98
Cheetah++, KA59 NVAX CPU
InfoServer 100/150/1000
General purpose storage server (disk, CD-ROM, tape and MOP boot server) related to MicroVAX 3100 Model 10, running custom firmware, KA41-C CPU
MicroVAX 3300/3400
Mayfair, used KA640 CPU card
MicroVAX 3500/3600
Mayfair-II, used KA650 CPU card, September 1987
MicroVAX 3800/3900
Mayfair-III, used KA655 CPU card
VAXstation series
VAXstation II
MicroVAX II workstation configuration
VAXstation II/GPX
Caylith, hardware-enhanced, high-performance color graphics, December 1985
VAXstation 2000
VAXstar MicroVAX 2000 workstation configuration
VAXstation 3100 series
VAXstation 3100 Model 30
PVAX, KA42-A CVAX CPU
VAXstation 3100 Model 38
PVAX rev#7, KA42-B CVAX CPU
VAXstation 3100 Model 40
Model 30 in larger enclosure
VAXstation 3100 Model 48
Model 38 in larger enclosure
VAXstation 3100 Model 76
RigelMAX, KA43-A Rigel CPU
VT1300
X terminal (essentially a diskless VAXstation 3100 Model 30)
VAXstation 3200/3500
Mayfair/GPX, KA650 CVAX CPU
VAXstation 3520/3540
Firefox, two or four KA60 CVAX processors
VAXstation 4000
TURBOchannel bus
VAXstation 4000/VLC aka Model 30
PVAX2/VLC, KA48 SOC ("System On Chip") CPU, slim pizza box, accepting standard 72-pin parity SIMM modules
VAXstation 4000 Model 60
PMariah, KA46 Mariah CPU
VAXstation 4000 Model 90
Cougar, KA49-A NVAX CPU
VAXstation 4000 Model 90A
Cougar+, KA49-A NVAX CPU
VAXstation 4000 Model 96
Cougar++, KA49-C NVAX CPU
VXT 2000
X terminal based on SOC CPU
VAXstation 8000
Lynx, very rare high-end 3D workstation based on VAX 8200
VAX 4000 series
MicroVAX name dropped
VAX 4000 Model 50
VAXbrick, KA600 NVAX processor, CPU upgrade for MicroVAX 3x00 or VAX 4000-200
VAX 4000 Model 100/100A
Cheetah-Q, KA52 NVAX processor
VAX 4000 Model 105A
Cheetah-Q+, faster KA53 NVAX processor
VAX 4000 Model 106A/108
Cheetah-Q++, faster KA54/KA57 NVAX processor
VAX 4000 Model 200
Spitfire, KA660 SOC processor
VAX 4000 Model 300
Pele, KA670 Rigel 1.5 µm CMOS processor chipset,[7] mid-1989
VAX 4000 Model 400
Omega, KA675 NVAX processor
VAX 4000 Model 500/500A
Omega/N, KA680/KA681 NVAX processor
VAX 4000 Model 505A/600/600A
Omega/N+, KA690/KA691 NVAX processor
VAX 4000 Model 700A
Legacy, KA692 NVAX processor
VAX 4000 Model 705A
Legacy+, KA694 NVAX processor
KA820-AA CPU for 8250/8350
KA820-AA CPU for 8250/8350
VAX 8200/8300
Scorpio, one or two V-11 CPUs respectively, VAXBI backplane, January 1986
VAX 8250/8350
Faster Scorpios
VAX 6000 series 
x = number of processors, max 6 for the 600 series
VAX 6000 Model 2x0 aka VAX 62x0 series
Calypso,: used CVAX chipset, April 1988
VAX 6000 Model 3x0 aka VAX 63x0 series
Hyperion, CVAX+ 1.5 µm CMOS processor chipset, January 1989
VAX 6000 Model 4x0 aka VAX 64x0 series
Calypso/XRP, Rigel 1.5 µm CMOS chipset, mid-1989
VAX 6000 Model 5x0 aka VAX 65x0 series
Calypso/XMP, Mariah 1.0 µm CMOS chipset, October 1990
VAX 6000 Model 6x0 aka VAX 66x0 series
Neptune, NVAX 0.75 µm CMOS chipset, November 1991
VAX 6333
prepackaged cluster of VAX 6000 Model 300 series
VAX 7000 series
VAX 7000 Model 6x0
Laser/Neon, Up to six KA7AA NVAX+ processors, field-upgradable to Alpha AXP 64-bit processor(s) (ie. DEC 7000 AXP configuration), July 1992
VAX 7000 Model 7x0
Laser/Krypton, KA7AB NVAX5 processor(s)
VAX 7000 Model 8x0
Laser/Krypton+, faster KA7AC NVAX5 processor(s)
VAX 10000 Model 6x0
Blazer/Neon, VAX 7000 Model 6x0 with more I/O capacity and UPS as standard
VAXft fault-tolerant series
VAXft 3000 Model 310
Cirrus, CVAX+ CPUs, two-processor, lock-stepped fault tolerant system, February 1990
VAXft Model 110
slower, lower cost Cirrus
VAXft Model 410/610/612
Cirrus II, SOC CPUs
VAXft Model 810
Jetstream, NVAX+ CPUs

[edit] Miscellaneous

VAXstation 100 (VS100)
Graphics terminal based on a MC68000 microprocessor, intended to connect to a VAX system via Unibus, May 1983.[8]
VAXstation 500
Color successor to VAXstation 100, October 1985.[9]
VAX XXXX
BVAX, High-end VAX (never shipped)

[edit] Clones

A number of clones of VAX models, both authorized and unauthorized, were produced. Examples include:

  • Systime Ltd. of the United Kingdom produced clones of early VAX models such as the Systime 8750 (equivalent to the VAX 11/750).[10]
  • Norden Systems produced the ruggedized, Military-specification MIL VAX series.[1]
  • The Hungarian Central Research Institute for Physics (KFKI) produced a series of clones of early VAX models, the TPA-11/540, 560 and 580.[11]

[edit] References

  1. ^ a b Rainville, Jim & Howard, Karen, eds. (1997), VAX/VMS at 20, Digital Equipment Corporation, <http://h71000.www7.hp.com/openvms/20th/>. Retrieved on 13 October 2007 
  2. ^ The Computer History Simulation Project: MicroVAX II (1985)
  3. ^ micro.magnet.fsu.edu, Steal the best, retrieved 30 January 2008. The Russian phrase was: СВАКС... Когда вы забатите довольно воровать настоящий лучший
  4. ^ The Computer History Simulation Project: CVAX (1987), retrieved 30 January 2008
  5. ^ VAX timeline, Hewlett Packard website
  6. ^ DIGITAL Computing Timeline
  7. ^ The Computer History Simulation Project: Rigel (1989)
  8. ^ Henry M. Levy (January 1984). "VAXstation: A General-Purpose Raster Graphics Architecture". ACM Transactions on Graphics (TOG) 3. ACM. doi:10.1145/357332.357336. 
  9. ^ Bell, Gordon (1986). "Toward a History of (Personal) Workstations". Proc ACM Conference on the History of Personal Workstations: 1-17, ACM. Retrieved on 2007-10-13. 
  10. ^ RAL Informatics Report 1984-85. Retrieved on 2007-10-15.
  11. ^ The TPA story. Retrieved on 2007-10-15.

[edit] External links