Three computer companies-Unisys Corp., Compac Computer Corp. and Apple Computer Inc.-on Monday unveiled products designed to step up the battle with industry giant International Business Machines Corp.

Unisys, formed in 1986 through a merger of Sperry Corp. and Burroughs Corp., introduced a long-awaited line of mainframe computers that it hopes will keep users of its aging Sperry line from defecting to rival mainframe vendors, notably IBM.

And Apple rolled out in San Francisco a new Macintosh that is faster than the current model and can work with data disks of other Apple computers and IBM-compatible machines.