Industry competitors took one of several approaches to the changing market. Some (such as Apple, Amiga, Atari, and Acorn) persevered with their independent and quite different systems. Of those systems, Apple's Macintosh is the only one remaining on the market. Others (such as Digital, then the world's second-largest computer company, Hewlett-Packard, and Apricot) concentrated on making similar but technically superior models. Other early market leaders (such as Tandy-Radio Shack or Texas Instruments) stayed with outdated architectures and proprietary operating systems for some time before belatedly realizing which way market trends were going and switching to the most successful long-term business strategy, which was to build a machine that duplicated the IBM PC as closely as possible and sell it for a slightly lower price, or with higher performance. Given the very conservative engineering of the early IBM personal computers and their higher than average prices, this was not a terribly difficult task at first, bar only the great technical challenge of crafting a BIOS that duplicated the function of the IBM BIOS exactly but did not infringe on copyrights.