The company's new computer called the Unix PC--is a relatively powerful desk-top machine that can accommodate up to nine users. The basic model, with about 512,000 characters of main memory, costs $5,095 and is available now. The Unix PC also has a video screen that can simultaneously display several "windows," or data from separate operations. It also features a "mouse," a hand-held device that allows the user topoint to symbols on the screen that represent a desired function. The new PC, which is being manufactured for AT&T by Santa Clara, Calif.-based Convergent Technologies, will also provide telecommunications hookups.