This was especially true given the way switch software was developed in the 1970s and 1980s. Many switches had proprietary minicomputer processors; some even used bespoke programming languages. Standard computer operating systems could not be used; telephone switch "generics" were, in effect, huge masses of embedded code built to exacting standards of reliability. GTE, with an 8% share of local lines, had built most of its own switches at its Automatic Electric subsidiary; its GTD-5 digital switch became widespread in GTE areas, with modest sales to other independents. But it did not prove very competitive; in 1989, GTE sold partial interest in Automatic Electric to AT&T, renaming the joint venture AG Communications Systems. This became part of Lucent, which became its sole owner in early 2004, merging it out of existence after more than a century. TRW Vidar, which had been for a time affiliated with independent LEC Continental Telephone, introduced the ITS-4/5, the first digital central office switch built in the United States. TRW shut it down in 1988; its assets, in the form of a new company called American Digital Switching, were acquired by 33 telephone companies that owned its switches and needed continuing support. That company was unsuccessful in introducing a planned new switch, the Cen- tura 2000, and faded out by 2000. Stromberg-Carlson, an old-line manufac- turer of electromechanical switches for rural carriers, was owned by defense contractor General Dynamics when it brought out its DCO, which proved fairly popular in the early 1980s. Later acquired by Siemens, the DCO was largely phased out in favor of Siemens' mainstream European digital switch, the EWSD. (The EWSD was the rare European import capable of meeting Ameri- can LEC requirements.) ITT Corp., once a global powerhouse whose North Electric Company sold switches to many independents, exited the telecommu- nications equipment business in the early 1980s when it sold its properties to French giant Alcatel. It too had been having problems makin