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Software Switch

Erna Hoover unjammed the telephone switchboard-from her bed in the maternity ward.

In 1947, bell labs launched a revolution with the introduction of the transistor, enabling everything from radios to computers to be made smaller and more cheaply. The transistor also made possible a less visible technology, one that allowed telecommunications to explode: electronic telephone switching. But the transistor was only one component of this development. Without software created by a researcher during her recovery from childbirth, the highly automated, computerized telecommunications age we take for granted would have been on indefinite hold.

In 1952, Bell Labs began exploring the development of electronic switching systems (ESS) for use not only by the public telephone systems but also for private business exchange systems. A newly hired researcher named Erna Schneider Hoover joined the team in 1954. Hoover was not a typical team member: not only was she female, but she came to Bell Labs with a degree in medieval history from Wellesley College and a doctorate in logic and philosophy of science from Yale.

Hoover contributed to the development of innovative software for stored program control (SPC) systems that processed calls in real time. After the birth of her first daughter, colleagues had difficulty convincing her to take her planned maternity leave. Then, while in the hospital after giving birth to the second of her three daughters, Hoover sketched out the first plans for a program to monitor the frequency of incoming calls and automatically adjust the acceptance rate, eliminating the danger of system overloads.

Hoover’s innovation eventually earned her a position as the first female department head at Bell Labs. And in 1971, it earned her one of the first software patents ever granted.

The first stored program control system went into service in a private business in 1963. Shown above, Bell’s No. 1 ESS went into commercial service in the public network in 1965. By 1983, 1,800 of the switching systems served 53 million subscriber lines. Today, businesses and public systems alike are using a direct descendant of the first system: AT&T’s No. 5 ESS. Even the Internet relies on SPC to help route the billions of e-mails coursing through the system daily.

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