The growth of Apple's market share stalled in October, just a month after a record increase, a research firm has reported.

According to Net Applications, Apple's operating system accounted for 6.55 per cent of all systems that browsed the 40,000 sites the company monitored in October, down slightly from 6.61 per cent during the month before and a significant change in direction from September, when Mac OS X posted a gain of about half a percentage point over August.

The slip - the first since July - may be due to sales slowing after the company wrapped up its annual back-to-school promotion in mid-September. Two weeks ago, during a conference call with Wall Street analysts, Apple executives called the promotion "extraordinary" and intimated that its sales might dampen short-term demand.

"We had just a fantastic September quarter, but really back-to-school and our higher-end results were an all-time high for the company," said Peter Oppenheimer, the company's chief financial officer. He added that unlike in years past, Apple might not be able to beat the just-finished quarter's sales during the holiday season. "This year, it's possible that Mac sales could be sequentially a little lower, given the extraordinary success of the back-to-school promotion," Oppenheimer said.

The stagnation of Mac market share may also be connected to the release of Mac OS X 10.5, aka Leopard, on 26 October, as some buyers postponed purchases until after Leopard's launch to ensure machines had the new operating system pre-installed.

Net Applications' data also showed that October was also the first month since Apple switched to Intel processors that the newer Macs accessed the Internet in greater numbers than older, PowerPC-equipped Macs. Last month, Intel-based Macs accounted for 3.41 per cent of all machines, in comparison with 3.14 per cent for PowerPC Macs. In September, Macs running the older processors still outnumbered Intel systems by 3.38 per cent to 3.23 per cent.

On the Windows front, Net Applications said that Vista, Microsoft's newest operating system, gained market share for the ninth consecutive month, ending October at 7.91 per cent, up from 7.38 per cent in September.

Computers running Windows 2000, XP or Vista accounted for 90.14 per cent of those that connected to the web last month, down slightly from the year's high of 90.55 per cent in July.