Overall worldwide PC shipments totaled 87.5 million units in the third quarter, down 8.3 percent compared to the same quarter last year, Gartner said.

The third quarter, which includes the back-to-school season and is usually strong for PC shipments, was hit with weak economies globally and by buyers moving to smartphones and tablets for their computing. In addition, a new category of thin and light laptops called ultrabooks failed to spark a revival in PC shipments during the third quarter, IDC said.

Looking ahead, the research firm expects a continued weak market for PCs until the release of Microsoft's Windows 8, said David Daoud, a research director at IDC, in an interview.

The U.S. presidential election on Nov. 6 could also help the PC market, he said, by bringing some clarity to the U.S.'s economic plans and thus encouraging vendors to invest in new product development.

Vendors have been trying to clear out their Windows 7 PC inventory, and demand dropped as buyers waited for Windows 8 to arrive, Daoud said. The new OS could help PC sales start to recover in the fourth quarter and into 2013.