SAN FRANCISCO - A report released on Thursday showed that Microsoft's Windows 8 gets to a slow start, as sales of devices running on Windows system have fallen 21 percent year-on-year during the initial four weeks after the debut of Windows 8.

Since Windows 8's launch on October 26, sales of notebook computer running on Windows operating system fell 24 percent and desktop computer sales dropped 9 percent, compared to the same period last year, market research firm The NPD Group said in the report.

According to the report, consumer Windows personal computer (PC) and tablet computer market did not get the boost it needed from the launch of Windows 8 in the United States.

"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," said the report.

"We still have the 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," it noted.

Meanwhile, the report found that the Windows 8 tablet sales have been "almost non-existent, with unit sales representing less than 1 percent of all Windows 8 device sales to date."

Microsoft announced on Tuesday that 40 million Windows 8 licenses have been sold one month after the new system was officially launched.

Analysts pointed out that the number include all sales, including those to original equipment manufacturers (OEMs) and other partners and it's possible that quite a few of the licenses haven't actually found their way to consumers yet.