RCA Spectra 70

The RCA Spectra 70 was a line of electronic data processing (EDP) equipment manufactured by the Radio Corporation of America’s computer division beginning in April 1965. The Spectra 70 line included several CPU models, various configurations of core memory, mass-storage devices, terminal equipment, and a variety of specialized interface equipment.

The system architecture and instruction-set were largely compatible with the non-privileged instruction-set of the IBM System/360. While this degree of compatibility made some interchange of programs and data possible, differences in the operating system software precluded transparent movement of programs between the two systems.

System Overview

Four models of the Spectra 70 CPU were offered in 1965, ranging from a small system (70/15) to the large scale (70/55.) Some of the main features were:
* The systems were upward-compatible, allowing programs written for a smaller model to run on any larger machine in the series.
* Larger machines in the series were also faster, with memory access times ranging from two microseconds in the 70/15 to 0.84 microseconds in the 70/55.
* Memory capacities ranged from a minimum of 4,096 bytes in the 70/15 to a maximum of 524,288 bytes in the 70/55.
* All used the Extended Binary Coded Decimal Interchange Code (EBCDIC) of eight bits plus parity for internal data representation.
* The use of a standard electrical interface allowed the same peripherals to be used with any CPU model in the series.
* Simultaneous input and output was accomplished by the use of intelligent communication channels. Like the IBM 360, two types of channel were available (on all but the 70/15): selector channels which could address up to 256 devices (one at a time), and multiplexer channels which could simultaneously address up to 256 channels by time-sharing the channel. While multiplexer channels were available on models 70/25, 70/45, and 70/55, the 70/15 could only support selector channels.

Models

Model 70/15

The RCA Model 70/15 was a small-scale processor that could still support a variety of applications. Memory limitations and relatively low processing speed made its use as a stand-alone computer system somewhat impractical.

The 70/15 was often used as a satellite processor for larger systems or used as an intelligent terminal for remote job entry. Typical applications of a satellite processor would include card-to-tape conversion, card/tape-to-printer report generation, tape-to-card punching, input pre-processing and verification, or tab-shop tasks like file sorting, merge, and data selection.

Two memory configurations for the 70/15 were available: either 4.096 bytes or 8,192 bytes of core memory. The memory cycle time for a 70/15 was 2 microseconds per byte of information.

Model 70/25

The RCA Model 70/25 was a small-to-medium scale computer system that supported a wider variety of applications, including use a free standing system. In large installations, the 70/25 might also be used as a subsystem in a multi-processor complex. High throughput was facilitated by the use of fast memory and multiple simultaneous input/output streams. Equipped with selector channels and a multiplexer channel, the 70/25 could concurrently operate eight low-speed devices in addition to eight high-speed devices.

Memory capacities for the 70/25 ranged from a minimum of 16,384 bytes to a maximum of 65,536 bytes. The memory cycle time was 1.5 microseconds to access one 32 bit word (4 bytes.)

Model 70/45

The RCA Model 70/45 was a medium scale processor of relatively good performance for its time. A floating-point processor was available as an option and the 70/45 was considered suitable for commercial, scientific, communications, and real-time applications.

With a communications multiplexer, the 70/45 could accommodate up to 256 communication lines for interactive use as well as batch processing. Thus, the 70/45 was ideal as the core of a multi-system installation. The 70/45 was one of the first computer systems to use monolithic integrated circuits in its construction. This level of integration was to become the defining characteristic of third-generation computers.

Memory capacity for the 70/45 ranged from a minimum of 16,384 bytes to 262,144 bytes. The memory cycle time was 1.44 microseconds to access two bytes (one half word) of information.

Model 70/55

The RCA Model 70/55 was a medium-to-large scale processor with excellent processor characteristics well suited to both scientific and large-scale commercial processing. The 70/55 maintained a high-throughput capability by offering up to 14 simultaneous job-streams. Like the 70/45, the Model 70/55 made extensive use of monolithic integrated circuits.

Memory capacity for the 70/55 ranged from 65,536 bytes of core memory to 524,288 bytes. The memory cycle time was 0.84 microseconds to access four bytes of information.

Input/Output Devices

Input-output devices on the Spectra 70 series were specifically designed to interface with all models of the Spectra processor using the RCA Standard Interface. Initial product offerings in 1965 included:

# Card punches that were fully buffered and able to operate at 100 or 300 cards per minute, depending upon the specific model.
# Three models of printers were offered: a medium-speed printer running at 600 lines per minute, a high-speed printer running at 1,250 lines per minute, and a bill-printer running at 600 lines per minute on continuous forms and 800 lines per minute on card-stock. Like the card punches, the printers were fully buffered.
# The Spectra optical card reader was able to read at up to 1,435 cards per minute with optional mark-sense reading available.
# Paper-tape capability was offered with 5, 6, 7, or 8 channel tape punches and readers. The punched tape reader operated at 200 characters per second and the tape punch ran at 100 characters per second.
# Three versions of magnetic tape were available running at 30, 60, or 120 kilobytes per second. In purely numeric mode, the tape reading and writing was performed at 240,000 digits per second. All tape drives were “industry” (meaning IBM) compatible and contained automatic error-checking systems. Either 7 or 9 channel tape code could be used and tapes could be written in the forward direction and read in both forward and reverse directions.
# Mass storage was available in the form of both magnetic drum and magnetic disc with an interchangeable disc-pack capacity of 7.25 MB at a data interchange rate of 156 kbit/s. The high-speed drum had a capacity of 1 MB with an average access time of 8.6 milliseconds.
# The Videoscan Document Reader was an optical-character-recognition scanner with a speed of 1,300 documents per minute. This was primarily used to scan checks and similar transaction documents.

ee also

* History of computing hardware (1960s-present)
* RCA