Dispensing the latest news, financial information and electronic mail via its large computers in McLean, Virginia, the Source operates much like other timesharing data bases and networks accessible from any telephone in the nation or the world.
    As a network user, you start by dialing a local telephone number and letting your modem-equipped personal computer connect to one of several data communications services. These networks, doing for computer messages what the phone company does for voice communications, link you up with the destination number you designate.
    Your call to the Source is received by a data network "engine," then switched to one of nine Source member computer systems assigned along with the ID number and password that allow access to your files. Each member computer, manufactured by Prime, has its own electronic mail system and two disk drives, each with three million bytes of storage. The Source computer facility, cooled by 110 tons of air conditioning (enough for ten average homes), contains a total of ten billion bytes of mass storage and ten billion bytes of internal memory. To guard against power failures, the system has a backup power supply consisting of 176 batteries, each four times the size of a car battery.
    Some information for the Source's data base is loaded into the member computers on magnetic tape. Dynamic data base information that has to be constantly updated is received and stored on a "back-end" computer until one of the "front-end" member computers calls for it. Other back-end computers are used for Source record keeping (customer data alone occupies 190 miles of tape) and development or as a backup if computers in the system need maintenance. With numerous interconnections within the system, over three hundred users at a time can access information on the Source.