Data General Nova
|Data General Super Nova'|
Edson deCastro was the Product Manager DEC (Digital Equipment Corporation) of the equally famous PDP-8 machine, generally considered by most to be the first true minicomputer. However deCastro was convinced it could be done even better, and left DEC to form Data General in 1968. The next year they released the Nova at a base price of $3,995 as the best small computer in the world, and soon Nova's were being sold in the tens per minute.
The big innovations of the Nova were not technical as much as packaging. Primarily the entire machine was built onto a single 15 inch by 15 inch printed circuit board, which could then be run off an assembly line with no wiring required. This greatly reduced costs over the PDP-8, which consisted of several boards and modules that had to be wired together by hand. This also made the Nova more reliable, which served it well in the lab setting.
The first models were available with 4k of core memory as an option, one that practically everyone had to buy, bringing the system cost to $7,995. Even here DG managed to innovate, packing several planes of very small core into a rectangular box lying along the left side of the case. Up to 32k could be supported in an external expansion box. Semiconductor ROM was already available at the time, and RAM-less systems with ROM-only became popular in industrial settings.
The original machines ran at 1.5MHz, but the Nova was soon upgraded with semiconductor RAM which allowed it to run at 3MHz to create the SuperNova.
The standardized backplane and I/O signals that implemented a simple but effective I/O design made interfacing programmed I/O and Data Channel devices simple compared to other machines of the day. The backplane had wirewrap pins that could be used for non-standard connectors or other special purposes.
It was a 16-bit, four accumulator and each instruction was contained one word. The instruction format could be broadly categorized into one of three functions: 1) register-to-register manipulation, 2) memory reference, and 3) input/output.
The register-to-register manipulation was almost RISC-like in its bit efficiency; and an instruction that manipulated register data could also perform tests and even elect to discard the result.
The Nova's biggest competition was from the newly-born DEC PDP-11 computer series, and to a lesser extent the venerable DEC PDP-8 systems. Some have said that the Nova was pretty crude compared to its competitors, but it was quite effective and very fast for its day, at least at this low-cost end of the market. In fact, the SuperNova computer's 300 nanosecond cycle time was the fastest minicomputer for over a decade following its introduction. The Nova influenced the design of both the Xerox Alto (1973) and Apple I (1976) computers.
There are even 16-bit Novas and Eclipses running today (2003) in a variety of applications worldwide.
There is a diverse but ardent group of people worldwide who restore and preserve legacy 16-bit Data General systems, and a web search of Data General Nova, Eclipse, RDOS, or the various other DG-related keywords should yield good results. Bob Supnik's fantastic SimH project  includes a basic Nova emulator in a user-modifiable package, and SimuLogic's web site  attempts to archive everything that is DG plus provide free and commercial products.