The Datacomputer was an ARPANET-connected database system supported by the Computer Corporation of America in Cambridge, Massachusetts. It was intended as a computing utility sharing resources among multiple ARPA projects, in particular in seismology and climatology. It operated from August 1973[1] until 1980.
It was hosted on a DEC PDP-10 running the TENEX operating system (ARPANET host CCA-TENEX, address 31)[2] and was designed to support 3 trillion bits of storage (375 GB). Besides storage, the Datacomputer also offered data conversion utilities which supported the multiple data formats used at the time.[3]
The largest user of the Datacomputer was ARPA's Seismic Data Analysis Center (SDAC) (Alexandria, Virginia), which monitored underground nuclear tests.
The Datacomputer manipulated data using a custom Datalanguage.[4] A sample retrieval request:
OPEN RESULTLIST ; OPEN WEATHER ; FOR WEATHER.STATION WITH REGION EQ 'MASSACHUSETTS' FOR RESULTLIST.RESULT, OBSERVATION WITH TEMPERATURE.MAX GT '300' /* DEGREES KELVIN */ RESULT.CITY = STATION.CITY ; RESULT.DATE = OBSERVATION.DATE ; RESULT.TEMPERATURE = OBSERVATION.TEMPERATURE ; END ; END;
The Datacomputer hardware had a three-level store: primary core, secondary hard disk, and tertiary mass storage. At the time, disk cost about $20/megabit, while mass stores, typically robotic magnetic tape systems, cost about $1/megabit. The service started in 1973 with disk storage only; tertiary storage using Ampex's Terabit Memory System (TMS) hardware, based on videotape technology, was to come on line in 1975.[5] In 1979, TMS's capacity was 175 billion bits (22 GB), and the total data stored was over 500 billion bits (62 GB)[6]