U.S. PC sales dropped by more than a fifth when compared compared to sales during same period in 2011.
NPD has said U.S. sales of Windows devices during the four-week launch of Windows 8 dropped 21 percent when compared to the same period a year ago.
The research firm said that the already-declining sales of notebooks decreased further by 24 percent. Desktop sales, meanwhile, sunk by 9 percent.
"After just four weeks on the market, it's still early to place blame on Windows 8 for the ongoing weakness in the PC market," Stephen Baker, vice president of industry analysis at NPD, said. "We still have the whole holiday selling season ahead of us, but clearly Windows 8 did not prove to be the impetus for a sales turnaround some had hoped for."
During the four weeks since its launch on October 26, Windows 8 was responsible for 58 percent of all Windows device sales. However, comparatively, Windows 7 accounted for 83 percent during its initial four weeks of availability.
Windows 8 tablet sales have been "almost non-existent," Baker said. It accounted for less than 1 percent of all Windows device sales during the four weeks. Initial sales of Windows 8 devices were also negatively impacted by weak sales of Windows 7 devices during the back-to-school shopping season that left retailers with a considerable amount of unsold inventory.
That said, the average selling prices of Windows devices are said to be higher than they were in 2011. The average price of a Windows 8 notebook increased by about $80 when compared with a Windows 7 notebook a year ago. The increase was partly due to strong sales of Windows 8 touch-screen devices, as well as an increase in the price for mainstream notebooks.
Windows 8 desktops' average selling price climbed by 10 percent due to demand for all-in-one PCs, in addition to a rise in the price of mainstream desktops.
"The strong performance of Windows 8 notebooks with touchscreens, where Windows 8 truly shines, offers some reason for optimism," Baker said. "These products accounted for 6 percent of Windows 8 notebook sales at an average price of $867 helping to re-establish a premium segment to the Windows consumer notebook market."
Despite selling 40 million Windows 8 licenses, sales for the operating system is said to be "well below" Microsoft's projections. The platform has also been criticized for its part in the ailing growth of the PC industry.