Mission | Main Page | Exhibit Hall | Your Contribution | Credits | Links



A Nova 1200 console
A Typical RDOS machine: Nova 1210 CPU

In 1969, as the NOVA was introduced, Data General knew the machine needed software. Initially, the only offering was SOS, the Standalone Operating System, which used paper tape to provide a rudimentary program development environment. In 1970, DG announced DOS, which allowed the machine to use the new disk drives DG purchased from Diablo.

But the NOVA was a very capable little 16-bit minicomputer, and could provide the speed and power to multitask, and to efficiently act as an industrial process controller in real time. To expand the market, DG designed a "Standard" operating system for it, RDOS, the Realtime Disk Operating System. Unlike the earlier SOS and DOS systems, RDOS provided for up to 32 separate tasks that could execute independently in the same memory space.

RDOS 1.00 began beta in late 1971, and was officially announced in 1972. Initially, the system supported a small number of small disks, the most popular of which was the Diablo 2.5 meg removable cartridge. Also supported were "dumb" serial devices, a 9-track 800 BPI tape drive subsystem, and paper tape to read in all those old SOS programs.

RDOS was immediately popular, as it was a capable and relatively easy-to-use interactive system for both developing programs and for running them. From the start, RDOS was a multitasking OS, although in today's terms actually "multithreading" is a more accurate term. A single RDOS program could start and control up to 32 "tasks" within its 64K address space. In addition, RDOS supported "Dual Programming", where two independent programs could run, one in background, one in foreground. Each could manage its own set of multiple tasks.

As NOVA hardware grew to include a memory mapping option that extended memory above the 64KB limit, new versions of RDOS were introduced to support the new hardware. The original flavor of RDOS was now "Unmapped" RDOS, and the new hardware was supported by "Mapped" RDOS. This latter version took advantage of the mapping hardware to provide two separate 64KB programs running at once.

Subsequent releases supported the growing array of DG disk subsystems. In 1975, Data General announced the Eclipse line of more powerful 16-bit minis, and the Eclipses had their own version of RDOS, which was completely compatible with NOVA RDOS, only in theory at least it took advantage of the more sophisticated Eclipse instruction set to make the operating system both smaller and faster, maximizing space for user programs. As release followed release, RDOS accumulated a number of native languages, including FORTRAN, ALGOL, Multiuser BASIC, Business BASIC, and DG/L, DG's own development language. Each of these was sold separately, however. Vanilla RDOS off the tape supported only Assembler.

Release 6 of RDOS in 1978 supported the new, expanded NOVA/3 line as well as newer Eclipses such as the S/130. This year saw a flurry of DG products, including the Nova-on-a-chip (MicroNova), and the specially packaged "Commercial Systems", which were standard Nova and Eclipse processors and peripherals in a series of standard configurations with a new DG language "Interactive COBOL" and a "mature" operating system called ICOS for Interactive Cobol Operating System. ICOS was really RDOS in a thin disguise. These systems proved very popular and many were installed in small businesses throughout America and the world.

The RDOS architecture and its little brother DOS (Diskette Operating System) on the MicroNova, and near-twin ICOS on commercial systems probably peaked in 1979 or 1980, as the newer, far more sophisticated Advanced Operating System (AOS) on the Eclipse line began to make slow but steady progress, held back by its extravagant hardware demands (512K of memory, floating point and Character instruction set options, and minimum 10MB of disk).

By 1982, RDOS began to fade as DG customers began upgrading to the new 32-bit line of Eclipses which ran the 32-bit AOS/VS operating system. A new RDOS flavor, DG/RDOS was introduced for the Desktop Generation line of microcomputers.

The last supported version of RDOS is 7.5, which is what we have here in the museum for you to try. In 1986, RDOS fell in "Support Category C" which means no new releases will be issued by DG.

RDOS was never popular in academia, as other operating systems similar to it were, and hence its base of users who fondly remember it as their "first OS" is small. Never spectacular, its role was as a fast, reliable workhorse for a proprietary computer line.

But no telling how many RDOS systems are still in use, their operators barely aware of the software. In the late 80's I remember taking a tour of a medical facility where they showed off their CAT scanner, and on the screen I saw the familar R prompt, while around the corner the Eclipse S/280 that ran the whole show sat quietly doing its thing.

Mission | Main Page | Exhibit Hall | Your Contribution | Credits | Links