Tablet cannibals have taken as big a bite out of Mac growth as they have out of personal computers in general, showing that Apple is not immune to the seismic shift it triggered with the iPad.
During the 12 months preceding Sept. 30, 2013, the end of Apple's fiscal year, Mac sales contracted 10% compared to the same period a year earlier.
During the same stretch, PC shipments declined 11.5%, according to research firm IDC.
Not only have the declines between Macs and PCs been similar, so has the timespan of those losses. The Mac has been on a four-quarter contraction, while PCs overall have posted shortfalls for six.
The two haven't always been in sync.
In the second half of 2009 (see chart below), both Mac and PC shipments rose rapidly as the Great Recession faded and businesses and consumers re-opened their wallets to buy new machines. On the PC side the spree was prompted by Windows 7's debut and pent-up demand for replacement PCs after buyers had spurned its predecessor, Windows Vista.
But in 2010 and 2011, as Mac sales continued a torrid pace of growth -- above 23% for four straight quarters -- PC gains could not keep up. They began slumping, going negative in the first quarter of 2011 and never climbing above 5% that year. Meanwhile, double-digit Mac gains came to a halt only in the first quarter of 2012.
The Mac's greater stamina in sustained growth was in contrast to the fading fortunes of PCs, which analysts attributed to increasing defections to tablets, and then in late 2012, Windows 8's failure to rejuvenate the industry.
Under that thesis, tablets were the primary cause of slowing PC shipments, as dollars and time once spent on personal computers were diverted to tablets. That, in turn, led to even fewer PC purchases as consumers and some businesses realized that even if they still needed computers, they could greatly extend the time between replacing systems because older machines were still able to do the tasks demanded of them.
The numbers show that the Mac succumbed to noticeable cannibalization, too, just later than the PC.
While some might argue that Mac owners continued to buy new systems even as they acquired tablets, a more likely explanation is that Apple's ability to maintain growth was caused by a surge of new users. In 2011, for example, a year when PC shipments grew by less than 2%, the Mac's share of online users -- as tracked by metrics firm Net Applications -- increased by 22%, as some consumers switched from Windows PCs to Macs.
That influx of new Mac owners masked whatever sales declines would have shown up otherwise.
The Mac's eventual contraction, which started in the fourth quarter of 2012 and continued through the first three quarters of 2013, could also be used to refute the theory that Windows 8 was the prime cause of the PC industry's slump during that same period.
Some have blamed Windows 8 for the 2012-and-later decline, saying that customers avoided buying new machines because they'd heard the OS was confusing, relied on touch or had too few apps. While Windows 8 most certainly contributed to lower PC shipments, the fact that Macs also lost momentum at the same time, and without a similar OS headwind, is a sign that all personal computers have suffered more from a broader trend -- namely, the popularity of tablets -- than from a specific operating system's problems.
Cannibalization of Macs should not come as a surprise: Apple has acknowledged the tablet threat for more than a year. However, Apple was able to accept cannibalization -- something PC makers and Microsoft have had a harder time doing -- because it had the iPad to capture deserting dollars. In the last four quarters, Apple sold 71 million iPads, more than four times the number of Macs during the same time.