RCA Spectra 70 | 1965

RCA Spectra 70

The RCA Spectra 70 was an electronic data processing (EDP) equipment line manufactured by the RCA computer division starting in April 1965. The Spectra 70 line included various central processing unit (CPU) models, core memory configurations, large-scale storage devices, terminal equipment, and specialized interface equipment.

The system architecture and instruction set were mostly compatible with the IBM System/360’s non-privileged instruction set, using the EBCDIC character set. This compatibility allowed for some program and data exchange, but the differences in operating system software made program migration between the two systems difficult.

In the late 1960s, intense competition emerged in the large computer market, and in 1971, RCA sold its computer division and the Spectra 70 line to Sperry Rand. This sale resulted in significant financial losses for RCA.

Announced in April 1965, the Spectra 70 was composed of various models ranging from small systems (70/15) to large systems (70/55). These systems were upward compatible, meaning programs written for smaller models could run on larger machines. The larger the model, the faster it operated, with memory access times shortened from 2 microseconds for the 70/15 to 0.84 microseconds for the 70/55. Memory capacities ranged from a minimum of 4,096 bytes (4KB) for the 70/15 to a maximum of 524,288 bytes (512KB) for the 70/55. All models used EBCDIC, which added parity to the standard 8-bit representation of data. The standard electrical interface allowed all CPU models to use the same peripheral devices.

Simultaneous input and output were handled via intelligent communication channels. Similar to the IBM 360, the system offered both selector channels and multiplexed channels, enabling communication with various devices simultaneously. The Spectra 70 series featured a total of 144 instructions and supported optional floating-point operations. The 70/15 and 70/25 models did not support floating-point instructions.

All systems ran RCA’s actual memory operating systems, DOS and TDOS. The 70/45 model supported RCA’s 70/45 Basic Time Sharing System (BTSS), allowing up to 16 simultaneous users. The Spectra 70/46, 70/61, and later RCA 3 and 7 models, which supported virtual memory, could run RCA’s Virtual Memory Operating System (VMOS), originally called TSOS (Time Sharing Operating System). TSOS was the first demand-based, page-replacement virtual memory operating system on the market.

The Spectra 70 series was later supplemented with the RCA 2, 3, 6, and 7 series, which competed with the IBM System/370. The RCA 2 and 6 models ran the batch operating system OS/70, while the RCA 3 and 7 models ran VMOS. Some English Electric System 4 mainframes were rebranded as Spectra 70 models, while others were replica models of the IBM System/360, based on the RCA Spectra 70.

The 70/15 model was a small, limited system supporting only 25 instructions and was not downward compatible with the other Spectra 70 models. It was impractical as a standalone system due to its memory limitations and relatively slow processing speed. However, it was used as a satellite processor for larger systems or for remote job input via intelligent terminals, handling tasks like converting cards to tape format, connecting cards/tapes to printers, and sorting and merging data files.

The 70/15 had a memory capacity ranging from 4,096 bytes to 8,192 bytes, with a memory cycle time of 2 microseconds. Programs were executed from punch cards or magnetic tapes, and the 70/15 weighed 600 pounds (270 kg).

The 70/25 model was a mid-range system supporting a wider range of applications, sometimes used as a subsystem for larger systems. It supported high-speed memory and multiple simultaneous input/output streams, operating up to 8 low-speed and 8 high-speed devices simultaneously through selector and multiplexed channels. The 70/25 model offered memory capacities from 16,384 bytes to 65,536 bytes, with a memory cycle time of 1.5 microseconds. This model weighed 1,200 pounds (540 kg).

The 70/35 model, announced in 1965, was a mid-range computer that provided a high-speed, cost-efficient data system. Using third-generation technologies such as integrated circuits, it offered fast performance at a relatively low cost. Its memory capacity consisted of two 16,384-byte core memories, providing a total of 32,768 bytes. Floating-point processors were available as an option, but the model had fewer features than the 70/45 and 70/55 models. The 70/35 weighed 1,500 pounds (680 kg).

The 70/45 model was a mid-range computer suited for commercial, scientific, communication, and real-time applications. It could accommodate up to 256 communication lines using a communication multiplexer and played a key role in building multi-system configurations. The 70/45 was one of the first computer systems to use integrated circuits, a hallmark of third-generation computers. It supported memory capacities ranging from 16,384 bytes to 262,144 bytes, with a memory cycle time of 1.44 microseconds. This model weighed between 1,900 and 2,700 pounds (860 to 1,220 kg).

 The RCA Model 70/46, introduced in 1967, is a modified version of the 70/45 with added virtual memory capabilities. Advertisements for this computer referred to it as the "Octoputer."

Programs could run either in 70/45 mode (without virtual memory) or in 70/46 mode with virtual memory enabled. The virtual addresses were 24 bits in length. Pages could be specified as either 2048 or 4096 bytes in size, depending on program requirements; however, 2048-byte pages occupied the lower half of a page frame in memory. The system allowed a maximum of 512 pages. Virtual memory is divided into segments of 64 pages, indicated by bits 1-5 of the virtual address. While the instruction set architecture defined up to 32 segments, only eight were used in the 70/46. Address incrementation wraps around segment boundaries. With 4KB pages, segments are 256KB in size, with a total virtual memory size of up to 2MB. With 2KB pages, these numbers are halved.

The RCA Model 70/55, released in 1966, was a medium-to-large scale processor with excellent performance for scientific and large-scale commercial processing. It supported up to 14 simultaneous job streams and made extensive use of monolithic integrated circuits, similar to the 70/45. Memory capacities for the 70/55 ranged from 65,536 bytes (64KB) to 524,288 bytes (512KB), with a memory cycle time of 0.84 microseconds for 4 bytes of information. The weight of this model ranged from 3,000 to 5,100 pounds (1.5 to 2.6 tons).

The RCA Model 70/60 was a later addition to the Spectra 70 series, announced in 1969.

The Model 70/61 was the virtual memory version of the 70/60 and was referred to as "Octoputer II" in some advertisements. The 70/60 and 70/61 were the first RCA mainframe computers capable of supporting 1MB of core memory, housed in four standard racks in a "T" formation. These machines later became the RCA 6 and RCA 7 models, and the original blue and white cabinets were replaced with a new, more modern design. Although fast and reliable, these computers arrived too late to challenge the IBM 360 product line’s dominance.

Input/output devices in the Spectra 70 series were specifically designed to interface with all Spectra models using the RCA Standard Interface. Initial products released in 1965 included:

• Card Punches: Fully buffered, capable of processing 100 or 300 cards per minute depending on the model.
• Printers: Three models were available—medium-speed (600 lines per minute), high-speed (1,250 lines per minute), and bill printers (600 lines per minute on continuous forms and 800 lines per minute on card-stock), all fully buffered.
• Spectra Optical Card Reader: Could read up to 1,435 cards per minute, with optional mark-sense reading.
• Paper Tape Devices: 5, 6, 7, or 8-channel tape punches and readers with a reading speed of 200 characters per second and a punching speed of 100 characters per second.
• Magnetic Tape Devices: Available in 30, 60, or 120 kilobytes per second, with tape drives compatible with IBM standards and automatic error-checking systems.
• Direct Access Storage: Including the high-speed 70/565 Drum Memory Unit (1MB capacity, average access time of 8.6ms), the 70/564 Disc Storage Unit (7.25MB disc pack, 156KB/s data interchange rate), and the 70/568-11 Mass Storage Unit (67MB removable magazines).
• Videoscan Document Reader: An optical character recognition scanner that could process up to 1,300 documents per minute, primarily used for scanning checks and transaction documents.