SDS-4

SDS-4 (Small Demonstration Satellite 4) is a small satellite (50 cm cube with mass of 50 kg) developed by JAXA and to be launched as a secondary payload on the Shizuku mission in mid-2012.

There are four rather specialised systems on the satellite:

SDS

Organizations

Politics

SDS 9 Series

The SDS 9 Series computers are a backward compatible line of transistorized computers produced by Scientific Data Systems in the 1960s and 70s. This line includes the SDS 910, SDS 920, SDS 925, SDS 930, SDS 940, and the SDS 945. The SDS 9300 is an extension of the 9xx architecture. The SDS 92 is an incompatible 12-bit system built using monolithic integrated circuits.

The 910 and 920 were first shipped in August, 1962. The 9300 was announced in June, 1963. The 925 and 930 were announced in 1964. The 940 was announced in 1965, and the 945 in 1968.

General description

All systems are 24-bit single address machines. Programmer-accessible registers are A (accumulator), B (extension), X (index), and P (program counter—14 bits), plus an overflow indicator. The 9300 had three index registers X1 through X3 which could be used as base registers to allow access to memory above 16K words. The W and Y registers are used for input/output.

Maximum address space is 2¹⁴ or 16,384 words (16K) on the 910 and 920; The 9300, 930, and 940 support up to 32K, although the method of accessing additional memory varies.

SDS 940

The SDS 940 was Scientific Data Systems' (SDS) first machine designed to support time-sharing directly, and was based on the SDS 930's 24-bit CPU built primarily of integrated circuits. It was announced in February 1966 and shipped in April, becoming a major part of Tymshare's expansion during the 1960s. The influential Stanford Research Institute "oN-Line System" (NLS) was demonstrated on the system.

After SDS was acquired by Xerox in 1969 and became Xerox Data Systems, the SDS 940 was renamed as the XDS 940.

History

The design was originally created by the University of California, Berkeley as part of their Project Genie that ran between 1964 and 1965. Genie added memory management and controller logic to an existing SDS 930 computer to give it page-mapped virtual memory, which would be heavily copied by other designs. The 940 was simply a commercialized version of the Genie design, and remained backwardly compatible with their earlier models (with the exception of the 12-bit SDS 92).