Unidata Series X


The Unidata x-series was initiated as part of January 1972 agreement between Siemens and CII. That agreement later joined by Philips in July 1973 assumed a new comon product line between the two manufacturers.

For reasons, perhaps revealing some genuine distrust between respective engineering divisions, if not between companies, that product line included five models intertwining CII and Siemens designs: X1 to Siemens, X2 to CII, X3 to Siemens , X4 and X5 to CII. A requirement was to offer an upward compatibility with Siemens Series 4000 (derived from RCA Spectra 70) and CII Iris (somewhat excessively considered as being a single product line).

The line was to be sold as Unidata 77xx product line, each company being a "Supply Center" for the whole consortium. The CII X2 model was sold as 7740..

The 7720 was the first model to be announced (January 15th 1974). The 7730, 7740, 7750 were announced together September 18th, 1974. However, the models X3 and X4 have never been delivered.


Central Systems Models

The X2 model is based around a microprogrammed processor with a 400 ns cycle time and a processing power of 400Kops (operations/second)
Its control store has words of 72 bits and contains 256 words of writable control memory plus 7K to 11 K words of ROM (size depending  on options by modules of 1K words). Diagnostics and extension microprograms may also be loaded directly from main memory.
The data path of the processor is 32-bits.

The system includes 16 levels of interrupts with a scratchpad of 16 registers per level.

Processor features include the interpreter of Unidata 7000 (a set 169 instructions), instructions retry, elapsed timer, time of the day clock and interval timer. Unidata instruction set is based on Siemens/RCA set (somewhat similar to IBM 360/370 set , 8-bit byte addressed, EBCDIC encoding)

Main memory is ECC (Hamming code) DRAM MOS chips (a first for CII). Its capacity vary from 96KB to 512KB (read access in 615ns write access in 785ns. Memory accesses are buffered by 16 words of  64-bits accessible in 150ns. The memory controller performs virtual addressing with protection by 4KB pages.

The IOC is integrated with the processor. It is composed of:
  - one  BYMUX with up to 256 peripherals (on 8 channels) with a max. rate of 140KB/s
  - one to four BLMUX (block multiplexing selector channels) at a rate of 1.5MB/s or 2 MB/s (according the data of one or two bytes). BLMUX may also operate in "selector mode" without multiplexing.
  - 0 to 2 "transparent "channels (DMA) with a data rate of 4MB/s used in particular for CII Iris disc controllers.

7740 uses a special service processor with a diskette drive for initialization and processor maintenance. It controls the system console (CRT display and serial printer) and allows remote maintenance of the system.

When announced , the 7740 was able to take over French Siemens park. After the take-over of CII by Honeywell-Bull in mid-1975, some work on X2 continued in CII-HB for approximately one year to fulfill customers and Unidata alliance until it was formally dissolved.


Peripheral subsystems were IBM compatible subsystems connected through IBM compatible (FIPS60 standard) block multiplexed channels. That allowed to buy subsystems in OEM conditions from compatible peripheral manufacturers (in particular Control Data), as well as to open potentially additional outlets to Siemens and CII peripherals.


The operating system was to be based on Siemens BS/1000 and is known as BS/2000. The requirement for a migration path for SIRIS 8 implied that X4/X5 sold in the CII area should run under a stand-alone emulator named Siris-8X. The conversion to BS/2000 was not envisioned until the late 1970s at the earliest and very few efforts were made  at CII for the X-native software.


The failure of the Unidata joint venture had attracted a large range of comments. It occurred around the same time as emerged the success of Airbus Industrie, yet based on a similar multinational structure.
Independently of the successful lobbying of CII-HB and French politics considerations, the top-down creation of a product line allowing the pursuit of CII and Siemens independences, would have needed , if not some financial links, at least a strong technical management for Unidata having the authority on all the components of the plan.
Additionally, as it was the case with CII, focalizing all the efforts against IBM mainframes (and marginally Honeywell-Bull's ones) and disregarding  minicomputers and terminals was probably a planning error and paving the way for failure.


Revision : 19 février 2002.