VAX 8000

The VAX 8000 is a discontinued family of minicomputers developed and manufactured by Digital Equipment Corporation (DEC) using processors implementing the VAX instruction set architecture (ISA).

VAX 8600

The VAX 8600, code-named "Venus", introduced in October 1984, is the successor of the VAX-11/785. It was originally to be named "VAX-11/790", but was renamed before launch. The VAX 8600 is a successful model and at the time was the best selling high-end VAX. It was succeeded by the VAX 8800 family in 1987.

The VAX 8600 had a CPU with an 80 ns cycle time (12.5 MHz) implemented with emitter coupled logic (ECL) macrocell arrays (MCAs). The CPU consisted of four major logical sections, the E Box, F Box, I Box and M Box. The E Box executed all instructions, including floating-point instructions through microcode. It had an arithmetic logic unit (ALU) and barrel shifter. The F Box, or floating point accelerator (FPA), is an optional feature that accelerates floating-point instructions as well as integer multiplication and division. It is a two-module set consisting of an adder module and multiplier module. The adder module contains 24 macrocell arrays while the multiplier module contains 21. The I Box fetches and decodes instructions. The M Box controls the memory and I/O, translates virtual addresses to physical addresses and contains a 16 KB data cache.

The CPU used 145 MCAs. These were large scale integration devices fabricated by Motorola in their 3 µm MOSAIC bipolar process. They were packaged in 68-pin leadless chip carriers or pin grid arrays and were mounted onto the printed circuit board in sockets or were soldered in place. An additional 1,100 small scale integration (SSI) and medium scale integration (MSI) ECL logic devices were used. These ICs were spread out over 17 modules plugged into a backplane.

The VAX 8600 supports 4 to 256 MB of ECC memory and has eight slots on the backplane for memory modules. The system originally used 4 MB memory modules populated by 256 KBit metal oxide semiconductor (MOS) RAMs, which limited capacity to 32 MB. Modules with larger capacities were introduced later. The memory is controlled by the M Box, which also provides the memory array bus used to access the memory. This dedicated bus, which has an 80 ns (12.5 MHz) cycle time, contributes to the improved performance the VAX 8600 has over the VAX-11/780, which access memory via the Synchronous Backplane Interconnect (SBI) shared with I/O devices.

I/O is provided by the SBI. The VAX 8600 features one SBI but could be configured with two. The SBIs are provided by SBI adapters that interface the SBI to an internal adapter bus connected to the M Box. Each SBI has 16 slots for I/O devices, although only 15 are usable as one slot is reserved for the SBI adapter. With one SBI, that SBI has a bandwidth of 13.3 MB/s. With two SBIs, they have a total bandwidth of 17.1 MB/s. The adapter bus that interfaces the SBIs to the M Box has a bandwidth of 33.3 MB/s. Unibus and Massbus are also supported, provided by adapters that plug into the SBI. The VAX 8600 I/O cabinet contains a PDP-11 computer serving as the console, a Unibus card cage and provisions for mounting disk drives.

VAX 8650

The VAX 8650, code-named "Morningstar", was a faster version of the VAX 8600 introduced on 4 December 1985. It was originally to be named "VAX-11/795", but was renamed before launch. The VAX 8600 was the last VAX to be 100% compatible with the VAX-11/780 and VAX-11/785, to have the PDP-11 compatibility mode, and to use the SBI also used by the VAX-11/78x. The CPU had a 55 ns cycle time (18.18 MHz).

VAX 8200 and VAX 8300

The VAX 8200 and VAX 8300, code named "Scorpio", were mid-range minicomputers introduced on 29 January 1986.[1] The VAX 8300 was a dual-processor variant of the VAX 8200 and, with the VAX 8800 introduced on the same date, was among the first multiprocessor VAX computers. They used the KA820 CPU module containing a V-11 microprocessor operating at 5 MHz (200 ns cycle) and supported a maximum of 128 MB of ECC memory. It had one VAXBI bus and support for an optional Unibus.

VAX 8250 and VAX 8350

The VAX 8250 and VAX 8350 are faster models of the VAX 8200 and VAX 8300 introduced in early March 1987. They use the KA825 CPU module containing a V-11 microprocessor operating at 6.25 MHz (160 ns cycle).

VAX 8800 Family

VAX 8800

Code-named "Nautilus", this is the high-end model in the VAX 8800 family. It features two CPUs and two VAXBI buses as standard. The VAX 8000 CPU was a heavily pipelined design, slightly predating the first commercial MIPS and SPARC designs. Development of the VAX 8800 began in August–November 1982 and it was introduced on 29 January 1986.[1] When "Polarstar" systems and a new naming convention were introduced, the VAX 8800 was renamed to VAX 8820N to distinguish it from the VAX 8820 "Polarstar". After the name adjustments and upgrading to full SMP capability, the former VAX 8700 and VAX 8800 models became VAX 88x0 machines, where "x" represented the number of CPUs, i.e. VAX 8810, 8820, 8830 and 8840. The upgrade kit includes replacement numbers affixed to the front of the machine to reflect the new designation.

VAX 8700

The VAX 8700, code-named "Nautilus", was introduced in early August 1986. It is similar to the VAX 8800, but with only one CPU and VAXBI bus. It is upgradable to a VAX 8800. It became a VAX 8810 after the SMP upgrade and revised naming convention.

VAX 8550

The VAX 8550, code-named "Skipjack", was introduced in early August 1986. It is similar to the VAX 8700, but is not upgradable to the VAX 8800.

VAX 8500

The VAX 8500, code-named "Flounder", is a lower-performance variant of the VAX 8550, with microcode used to insert nops during operation to limit performance.

VAX 8530

The VAX 8530, code-named "Skipjack", is an upgraded VAX 8500 with the nops removed for improved performance. It was introduced in early March 1987.


Polarstar is a variant of Nautilus with one to four processors and an updated console processor. Models include the:

  • VAX 8810 - A single processor system
  • VAX 8820 - A two processor system
    • VAX 8842 - A cluster of two VAX 8820 systems
  • VAX 8830 - A three processor system
  • VAX 8840 - A four processor system
    • VAX 8974 - Introduced on 20 January 1987, it is a cluster of four VAX 8700 systems[2]
    • VAX 8978 - introduced on 20 January 1987, it is a cluster of eight VAX 8700 systems[2]


The VAX 8800 family is based on the NMI bus, which connected the CPU, memory controller and I/O adapters. The NMI bus is a 32-bit synchronous bus with a usable bandwidth of 64 MB/s.


The VAX 8800 family central processing unit (CPU) operates at 22.22 MHz (45 ns cycle time) and is implemented with discrete emitter-coupled logic (ECL) devices spread over eight modules. The majority of the ECL devices are macrocell arrays with 1,200 logic gates, while the general-purpose registers and floating-point units are custom logic devices developed by Digital. The CPU has 64 KB of cache implemented with 10 ns and 15 ns ECL random access memory devices.


The VAX 8800 and 8700 support one to eight memory array modules; the VAX 8550 and 8500, one to five. The memory array modules are installed in a dedicated backplane separate from the NMI backplane. The VAX 8800 and VAX 8700 support 4 to 32 MB of memory, the VAX 8500 and VAX 8550 4 to 20 MB, using the 4 MB memory module. When the 16 MB memory module was introduced, the memory capacity of the VAX 8800 and 8700 was increased to 128 MB, and that of the VAX 8550 and 8500 to 80 MB. Additionally when the 64 MB memory module was introduced, the memory capacity of the VAX 8800 and 8700 was increased to 512 MB and that of the VAX 8550 and 8500 to 320MB.

The memory system consists of three major parts, a memory controller, a transistor-transistor logic (TTL) bus and one to eight memory array modules. The memory controller is implemented with ECL gate arrays and resides on an NMI bus module. It implements a TTL bus to which memory array modules are connected. Three memory modules were available for the VAX 8800: a 4 MB module, a 16 MB module and a 64 MB module. The 4 MB array module is an eight-layer printed circuit board populated by metal oxide semiconductor (MOS) dynamic random access memory (DRAM) devices and medium-scale integration (MSI) FAST transistor-transistor logic (TTL) devices in roughly equal numbers. The 16 MB array module is similar to the 4 MB module, but contains eight surface-mounted daughter boards, each containing 2 MB of memory built from DRAMs.


The VAX 8800 uses the VAXBI bus for input/output. The VAX 8800 supports up to four VAXBI buses, with each bus supporting up to 16 I/O devices. The VAXBI bus is interfaced to the NMI bus by a NBI adapter containing a chip implementing the VAXBI bus protocol. The NBI adapter handles all CPU references and direct memory access (DMA) transactions to and from the I/O devices. The adapter operates at 5 MHz and asynchronously to the CPU as it generates its own clock signal. The NBI adapter consists of two modules, the NBIA and NBIB. The NBIA is the NMI side of the adapter, and the NBIB the VAXBI side.

VAX Console

The VAX Console is a DEC Professional Series PC-38N. This is a PRO-380 with a real-time interface (RTI) that is used as the console for the Nautilus family of processors. The RTI has two serial line units: one connects to the VAX environmental monitoring module (EMM) and the other is a spare that could be used for data transfer. The RTI's IEEE-488 interface was not used. The RTI's programmable 24 bit peripheral interface (PPI) is configured as three 8-bit ports for data, address, and control signals between the Nautilus system console interface and the VAX console. The console's primary function is to bootstrap the system. The Nautilus family of processors has no non-volatile memory. The console sets configuration registers, loads CPU microcode into the writeable controls store, performs processor module diagnostic tests, resets the TOY clock (time-of-year clock), logs certain types of errors, performs other supervisory functions, and is the interface for field service diagnosis and testing.[3]


  1. "Digital VAX Line".
  2. Sanger, "Digital To Offer Mainframes".
  3. VAX 8500/8550 System Hardware User's Guide. Digital Equipment Corporation. 1986. pp. 1–8.


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