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ari blokbland, vx company

Ari Blokland

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A working VAX 11/780 – revisited

Almost a year ago, I created my first VAX-11/780 on simh. This is Release 1.1 of the project, based on the Pi Zero.

VX Company started in 1987 under the name VX8000. In that year, the VAX 8000-series was the flagship of Digital Equipment Corporation. Exactly 10 years earlier, DEC had introduced the VAX-11/780, the first of a long range of mini- and mainframe computers. The last sets of VAXen left the factory in the year 2000.

The VAX has educated a generation of computer specialists. Its inheritance includes the “VUP”  (VAX Unit of Processing) and a number of open source and commercial emulators. These programs make it possible to run applications on VAX/VMS without the presence of the original hardware.

A working VAX 11 780 – revisited – blog04@4x

The VAX-11/780 shown here is built into a Raspberry Pi Zero computer. This runs a VAX-11/780, built upon the simh emulator platform. VAX/VMS V1.5 is installed on the virtual hardware. The system can also run the most recent VAX/VMS V7.3 version, including DECnet and TCP/IP.

The VAX has two Massbus disks (RM03), 8MB memory (the maximum amount for the first series and a DEUNA Unibus 10Mb/s Ethernet adapter, as well as a TE16 tape unit.

This virtual VAX delivers a performance of 4 VUPs, in other words four times as fast as the original VAX-11/780 from 1977.

How the characteristics have changed:

VAX-11/780 (1977) Raspberry Pi Zero (2015)
Dimension (typical) 60x48x30”
(1524x1219x762 mm)
(65x30x5 mm)
Instruction cycle time 200 ns (5MHz)
single CPU
1.1ns (900Mhz)
single core
Maximum RAM memory first 8MB,
later 128MB
Typical system disk RP05 (100 MB)
Power 240V 3-phase, 32A 5V, 1A


The advantage of the Pi Zero over the “standard” Raspberry Pi for this project is that the Pi Zero neatly fits into the VAX-11/780 model case that we have available. As shown below, the only cables leaving the model are the serial console line from the Pi GPIO head to the VT520 terminal, and the power cable. There is also room for a single Ethernet cable (via a USB-Ethernet converter connected to the Pi’s single USB port).

A working VAX 11 780 – revisited – blog@4x
A working VAX 11 780 – revisited – blog03@4x


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