sentences:  In the early 1980s, the timesharing market began collapsing, mostly due to the appearance in the marketplace of relatively lower cost IBM mainframe computers, such as the IBM 4300.STSC quickly changed its focus to supply APL services for in-house and the rapidly developing personal computer (PC) market.In 1982, STSC released "APL*Plus/PC", which was a very successful APL interpreter for the IBM personal computer.