Apple and Microsoft have been fighting it out in the PC industry since the early 80s. Back in 1984, the two companies were on more equal footing when it came to the sales of the individual operating systems on computers. Things changed over the 80s into the early 90s as the ratio between PCs sold versus the number of Macs sold hovered around 15 times as many PCs until around 1997.
In 1997, the number of PCs sold versus Mac computers sold surged to nearly 30 times as many PCs. That number continued to grow through 2004 where Microsoft had nearly 60 times as many PCs sold versus Apple's Mac computer. 2004 was in when the Mac computer began growing significantly in popularity, and the ratio started to decline for PCs rather quickly.
By 2005, the ratio was under 45 times as many PCs sold versus Macs and continued to decline through 2011 when the ratio was nearly identical to what was seen in 1985 at roughly 17 times as many PCs sold versus Macs. Assuming the trend of increasing Mac sales continues over the next few years we could see the ratio of PCs versus Macs match what it was back in 1984 or even go lower. The chart above comes from the research firm Asymco and illustrates the rise and fall very well. This chart only includes Mac computers, iPads and iPhones are not included according to the source.
[via Business Insider]