Varian Data Machines

DATA / Varian 620 registers
	Accumulator registers;
A	Register A
B	Register B
	Index register;
X	Index Register X
	Program counter;
	Status register

Varian Data Machines
Company type	Division
Industry	Computer hardware
Predecessor	Decision Control Inc. (DCI)
Founded	1967
Defunct	June 1977
Fate	Purchased by Sperry Corporation and merged into Sperry UNIVAC Minicomputer Operation
Headquarters	Newport Beach, California, United States
Products	Minicomputer systems (DATA/620, 620/i, 620/F, 620/L, Sperry V70 series)

Varian Data Machines functioned as a branch of Varian Associates focused on the development and marketing of minicomputer systems. Its entry into the minicomputer sector occurred in 1967 through the acquisition of Decision Control Inc. (DCI), located in Newport Beach, California. Due to intense market competition, the division was purchased by Sperry Corporation in June 1977 and subsequently merged into Sperry's UNIVAC segment, becoming known as the Sperry UNIVAC Minicomputer Operation.

Computers

DATA/620

Introduced in 1965, the initial DCI DATA/620 system was leased at $900 monthly, positioning it competitively against many contemporaneous computers. This model was a parallel-processing, binary 16-bit general-purpose digital computer equipped with magnetic-core memory expandable up to 32,768 words. An optional feature allowed handling data with an 18-bit word length. The fundamental machine cycle duration was 1.8 microseconds, while core memory access time measured 700 nanoseconds. Employing two's complement arithmetic, it incorporated four principal registers: accumulators A and B, an index register labeled X, and a program counter. Certain configurations supported microprogramming capabilities. The hardware front panel console facilitated machine control functions such as start/stop operations and direct examination or alteration of memory and registers without requiring an oscilloscope.

Constructed from discrete transistors arranged in a bit-sliced design, the system utilized circuit boards termed "VersaLOGIC," which operated at logic voltage levels of 0 V and -12 V. Its architecture and instruction set bore similarities to other minicomputers of the era like the Honeywell 316 and PDP-8 models. Key characteristics included:

Absence of a stack pointer, with subroutine return addresses stored at the initial word of each subroutine.
Capability to micro-code multiple operations within a single instruction (for example, simultaneously clearing registers A, B, and X).
Support for multi-level indirect addressing where instructions referred to the address containing an operand’s address.

Register A functioned as the main accumulator for arithmetic and logical operations, with the second operand fetched from memory. The first 2048 words were directly addressable; accessing the full memory range required using registers B or X as index registers or applying indirect addressing within the first 512 words. Additionally, operands could be addressed relative to the program counter (within a range of 512 words) or specified as immediate 16-bit values. An optional hardware enhancement introduced multiplication and division instructions that treated registers A and B together as a combined 32-bit register.

A DATA/620 system equipped with up to 8192 words of memory weighed roughly 400 pounds and had a power consumption rating of approximately 500 watts.

DATA 620/i

Introduced in June 1967, the 620/i utilized integrated circuit transistor–transistor logic from the 7400 series. Housed within a 19-inch rack, it operated with a power consumption of 340 watts at 120 V AC. The 620/F model offered an improved cycle time of 750 nanoseconds.

In 1968, the more durable R-620/i version was launched, followed by the cost-effective 520/i in October of the same year.

Varian 620/L

The 620/L-100, released in 1973, featured a cycle time of 950 nanoseconds and a chassis that was more compact compared to the 620/F. The Sperry V70 series, manufactured between 1972 and 1977, integrated semiconductor memory while maintaining compatibility with magnetic core memory.

Applications

Varian V72 computer systems were employed at Ontario’s Bruce Nuclear Generating Station as digital control units overseeing critical reactor and power plant operations. As of February 2017, these systems continued in service, with replacement plans set for 2018 and 2019.

External links

Documentation for Varian computers available at www.bitsavers.org (PDF format)