VAX-11

The VAX-11 is a discontinued family of superminicomputers developed and manufactured by Digital Equipment Corporation (DEC). They were first announced in 1977, and were the first computers to implement the Virtual Address eXtension (VAX) instruction set architecture (ISA). The VAX-11 processors also supported the user mode PDP-11 instruction set for backwards compatibility (thus the -11 in VAX-11). They were discontinued in 1988, having been supplanted by the MicroVAX family on the low end, and the VAX 8000 family on the high end.[1][2]

A VAX-11/780

VAX-11/780
VAX-11 registers
31 ... 23 ... 15 ... 07 06 05 04 03 02 01 00 (bit position)
General registers
R0 Register 0
R1 Register 1
R2 Register 2
R3 Register 3
R4 Register 4
R5 Register 5
R6 Register 6
R7 Register 7
R8 Register 8
R9 Register 9
R10 Register 10
R11 Register 11
Index registers
R12 / AP Register 12 / Argument Pointer
R13 / FP Register 13 / Frame Pointer
R14 / SP Register 14 / Stack Pointer
Program counter
R15 / PC Register 15 / Program Counter
Status flags
  I V N Z C Processor Status Word
    Floating Point Status Register

The VAX-11/780, code-named "Star", was introduced on 25 October 1977 at DEC's Annual Meeting of Shareholders.[3] It is the first computer to implement the VAX architecture. The KA780 central processing unit (CPU) is built from transistor-transistor logic (TTL) devices and has a 200 ns cycle time (5 MHz) and a 2 kB cache. Memory and I/O are accessed via the Synchronous Backplane Interconnect (SBI).

The VAX-11/780 supports 128 kB to 8 MB of memory (2 MB initially) through one or two memory controllers. Each memory controller supports 128 kB to 4 MB of memory. The KA780 has a 29-bit physical address space, allowing it to address a theoretical maximum of 512MB of memory. The memory is constructed from 4 or 16 kbit metal oxide semiconductor (MOS) RAM chips mounted on memory array cards. Each memory controller controls up to 16 array cards. The memory is protected by error correcting code (ECC).[4]

The VAX-11/780 uses the Unibus and Massbus for I/O. Unibus is used for attaching lower-speed peripherals such as terminals and printers and Massbus for higher-speed disk and tape drives. Both buses are provided by adapters that interface the bus to the SBI. All systems come with one Unibus as standard, with up to four supported. Massbus is optional, with up to four supported.[5] The VAX-11/780 also supports Computer Interconnect (CI), a proprietary network to attach disk drives and potentially share them with other VAX computers. Later, this feature was used to connect VAX computers in a VMScluster.

Digital used the performance of the VAX-11/780 as a reference point for describing the performance of subsequent VAX models. The performance of the VAX-11/780 became known as 1 VAX Unit of Performance (or 1.0 VUPS).[6] Other VAX models were rated as a multiple of the VAX-11/780's performance, for example, a 2.0 VUPS VAX would be twice as fast as the VAX-11/780.

VAX-11/782

The VAX-11/782, code-named "Atlas",[7] is a dual-processor VAX-11/780 introduced in 1982. Both processors share the same MA780 multiport memory bus and the system operates asymmetrically, with the primary CPU performing all I/O operations and process scheduling with the second, attached processor only used for additional computationally-intensive work. For multistream computation-intensive tasks the system delivers up to 1.8 times the performance of a VAX 11/780.[8][6]

VAX-11/784

The VAX-11/784, code-named "VAXimus",[7] is a rare quad-processor variant of the VAX-11/780. Similar to the VAX-11/782, it was an asymmetric multiprocessing system, with all four KA780 processors sharing the same MA780 multiport memory bus. Its performance was rated as 3.5 VUPS.[6]

VAX-11/785

The VAX-11/785, code-named "superstar", was introduced in April 1984.[9] Its KA785 CPU is essentially a faster KA780, with a CPU cycle time of 133 ns (7.52 MHz) versus the 200 ns (5 MHz) CPU cycle time of the KA780,[10] giving a performance of 1.5 VUPS.[6] The memory subsystem was also upgraded to support higher capacity memory boards.[11]

VAX-11/787

The VAX-11/787 is a possible dual-processor variant of the VAX-11/785. It is unclear whether any were produced.[7]

VAX-11/750
VAX-11/750

The VAX-11/750, code-named "Comet", is a more compact, lower-performance Bipolar gate array–based implementation of the VAX architecture introduced in October 1980.[12] The use of gate arrays decreased power consumption, and increased reliability compared with the VAX-11/780.[13] The KA750 CPU has a 320 ns cycle time (3.125 MHz), and a VUPS rating of 0.6.[6] The system could support up to 8MB with an L0011 memory controller, or up to 14MB with an L0022 memory controller.[14][15]

VAX-11/751
VAX-11/751

A ruggedized rack-mount VAX-11/750.[16]

VAX-11/730

Introduced in April 1982, the VAX-11/730, code-named "Nebula", is a still-more-compact, still-lower-performance bit slice implementation of the VAX architecture using AM2901 chips for the CPU. The KA730 CPU has a 270 ns cycle time (3.70 MHz), and a VUPS rating of 0.3.[6] It supported up to 5MB of memory.[17]

VAX-11/725

Code-named "LCN" ("Low-Cost Nebula"), it is a cost-reduced model of the VAX-11/730. It used the same KA730 CPU as the VAX-11/730, but was housed in a more compact enclosure which was designed to produce less noise and heat, making it more suitable for use in an office environment.[14] It suported up to 3MB of memory.

VAX-11/790 and VAX-11/795

The VAX-11/790 and VAX-11/795 were the original names for the VAX 8600 and VAX 8650 respectively.[18]

Remaining machines
A VAX 11 780 CPU backplane

The Living Computer Museum of Seattle, Washington maintains a VAX-11/780-5 (field-upgraded VAX-11/780) running OpenVMS 7.3. Request a login to try out this equipment and software.
The Computer History Museum of Mountain View, California has three VAX-11/780 systems, one VAX-11/725, one VAX-11/730, and one VAX-11/750 within its permanent collection.[19]
The RECHENWERK RECHENWERK Computer & Technikmuseum Halle in Halle, Germany holds a VAX-11/730 and a very rare east German clone of a VAX-11/780 named Robotron K 1840 in its permanent exhibition.
The Verde Binario retrocomputing association has a VAX-11/780 to which they dedicated a calendar.[20]

References
  1. Ed Thelen (August 2005). "VAX-11/780 11/750". ed-thelen.org. Retrieved 2021-01-03.
  2. "VAX 11/780, THE FIRST VAX SYSTEM". old-computers.com. Retrieved 2021-01-03.
  3. Digital Equipment Corporation. VAX OpenVMS at 20.
  4. "VAX-11/780 Hardware User's Guide" (PDF). bitsavers.org. 1979. Retrieved 2020-12-28.
  5. "VAX-11/780 Installation Guide" (PDF). bitsavers.org. January 1982. Retrieved 2020-12-28.
  6. "VAX CPU Model Summary". vaxmacro.de. Retrieved 2020-12-27.
  7. "Hardware Documentation - Machines DEC - VAX hardware reference". The NetBSD project. Retrieved 2012-08-24.
  8. VAX Product Sales Guide EG-21718-18 (PDF). Digital Equipment Corporation. May 1982. Retrieved 2012-08-24.
  9. DIGITAL Computing Timeline
  10. "VAX-11/785 Hardware User's Guide" (PDF). bitsavers.org. 1984. Retrieved 2020-12-28.
  11. DIGITAL Computing Timeline
  12. "VAX-11/750 Central Processor Unit Technical Description" (PDF). bitsavers.org. March 1981. Retrieved 2020-12-28.
  13. "Makings of a Comet: The VAX-11/750". cpushack.com. 2014-12-08. Retrieved 2020-12-28.
  14. "DEC VAX Hardware Handbook Volume 1 - 1986" (PDF). bitsavers.trailing-edge.com. 1986. Retrieved 2020-12-28.
  15. Dalby Datormuseum. "VAX-11/750". Retrieved 2020-12-28.
  16. Paul Hardy (1993-10-14). "VMS CPU Model Summary". iankitching.me.uk. Retrieved 2020-12-27.
  17. "VAX-11/730 CPU Technical Description" (PDF). bitsavers.org. May 1982. Retrieved 2020-12-27.
  18. "VAX 8000 Series". netbsd.org. Retrieved 2021-01-03.
  19. "CHM VAX-11 systems". Retrieved 2015-04-24.
  20. "MIAI/MUSIF 2018 calendar". Retrieved 2018-01-24.
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