"While there are a variety of PC share reports in the market, some don't measure the market in its entirety. The IDC analysis includes the very important workstation segment and therefore is more comprehensive. In that IDC report, HP occupies the No. 1 position in PCs," HP spokesman Mike Hockey wrote in an email.

Lenovo benefitted from building up its distribution channel and from "missteps" by its rivals, IDC said. HP is still trying to get its PC business back on track after reversing a plan to sell or spin off the division. Dell has been moving away from lower-margin PCs and focusing on products that yield bigger profits.

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.