It's no secret that PC sales have been, well, bad for awhile now. Sales of Apple's Mac computers, however, have held fairly well up for the most part.

That may be shifting.



In the third quarter, Mac sales dropped 11 percent to 1.9 million from the period a year earlier, according to an IDC report. What's more, Apple was the only company among the top five U.S. vendors to post a decline in shipments.

"The PC market in general has been in six quarters of consecutive decline, and it's getting cannibalized by tablet sales," BGC Financial's Colin Gillis told CNBC on Thursday.

"You go back and the peak actually happened in September of 2011. PC sales as a total are down 17 percent since then, and if you add up the numbers, it correlates with tablet sales. Tablets are cheaper, tablets are easier and the PC may wind up becoming more of a relegated, niche product."

