Datacomputer

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 1973 until 1980.

It was hosted on a DEC PDP-10 running the TENEX operating system (ARPANET host CCA-TENEX, address 31)[1] 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.[2]

The largest user of the Datacomputer was ARPA's Seismic Data Analysis Center (SDAC) (Alexandria, Virginia), which monitored underground nuclear tests.[3]

The Datacomputer manipulated data using a custom Datalanguage.[4] A sample retrieval request:[5]

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)[3]