Since the introduction of the Macintosh, Apple has struggled to gain a significant share of the personal computer market. At first, the Macintosh 128K suffered from a dearth of available software compared to IBM's PC, resulting in disappointing sales in 1984 and 1985. It took 74 days for 50,000 units to sell.[13]

By 1997, there were more than 20 million Mac users, compared to an installed base of around 340 million Windows PCs.[62][63] Statistics from late 2003 indicate that Apple had 2.06 percent of the desktop share in the United States, which had increased to 2.88 percent by Q4 2004.[64] As of October 2006, research firms IDC and Gartner reported that Apple's market share in the U.S. had increased to about 6 percent.[65] Figures from December 2006, showing a market share around 6 percent (IDC) and 6.1 percent (Gartner) are based on a more than 30 percent increase in unit sale from 2005 to 2006. The installed base of Mac computers is hard to determine, with numbers ranging from a conservative 3 percent[66] to an optimistic 16 percent.[67]

Three ways of measuring market share are: i) by browser hits, ii) by sales, and iii) by installed base. If using the browser metric, Mac market share has increased substantially in 2007[68]. However, results for market share measured as a percentage of current sales provides different results than when market share is measured by installed base.

Whether the size of the Mac’s market share and installed base is actually relevant, and to whom, is a hotly debated issue. Industry pundits have often called attention to the Mac’s relatively small market share to predict Apple's impending doom, particularly in the early and mid 1990s when the company’s future seemed bleakest. Others argue that market share is the wrong way to judge the Mac’s success. Apple has positioned the Mac as a higher-end personal computer, and so it may be misleading to compare it to a low-budget PC.[69] Because the overall market for personal computers has grown rapidly, the Mac’s increasing sales numbers are effectively swallowed by the industry’s numbers as a whole. Apple’s small market share, then, gives the false impression that fewer people are using Macs than did (for example) ten years ago.[70] Others try to de-emphasize market share, citing that it's rarely brought up in other industries.[71] Regardless of the Mac’s market share, Apple has remained profitable since Steve Jobs’ return and the company’s subsequent reorganization.[72] Notably, in a report published in the first quarter of 2008, it was found that the Apple Macintosh computers made up a total of 66% of all computers sold that were above $1,000, and 14% of all computers sold.[73]

Market research indicates that Apple draws its customer base from a higher-income demographic than the mainstream PC market. Higher income theoretically correlates with well-educated social behaviors, which may explain the platform’s visibility within certain youthful, avant-garde subcultures.[74] Steve Jobs speculates that “maybe a little less” than half of Apple’s customers are Republicans, “maybe more Dell than ours.”[75] This perception may or may not be accurate—several prominent conservatives, including Rush Limbaugh, are Mac users[76]—but it can only be reinforced by the company's pattern of political donations,[77] by Al Gore’s membership on its board,[78] and surely not least by Jobs’ own personal history.[79]