Apple’s latest iteration of OS X is off to a good start, with multiple reporting firms all suggesting that the installation base for Mavericks has hit around 10 percent or so of the total OS X installation base.

Massachusetts-based online ad network Chitika was the first out the gate(Opens in a new window) with a number, suggesting that Mavericks had surpassed a 10 percent installation rate within five days of the operating system update’s free launch.

A word about that: It’s likely that the free upgrade is partially the reason for the quick adoption. Or, at least, it’s a fair guess — Mountain Lion, the previously released “big update” to OS X, took all of a month or so to reach the adoption levels that Mavericks has seen within 10 days, and it cost Apple users $20 to upgrade.

As TechCrunch(Opens in a new window) noted, adoption rates for operating systems can be an “imprecise” measurement, which partially explains why there’s a bit of a gap between Chikita calling the 10 percent figure and fellow analytics firm NetMarketShare(Opens in a new window) coming out of the gate with its own 10 percent figure. According to the latter, as of this article’s writing, OS X 10.9 (Mavericks) is now up to a 0.84 percent share of the global PC installation base and a 10.9 percent share among all OS X users, period.

For those who enjoy the ever-present Microsoft-versus-Apple debate, here’s some additional ammo to toss back and forth among your tech friends: OS X Mavericks, in the short span of five days or so, has managed to hit half the adoption rate (among the global PC installation base) Windows 8.1. Both operating system updates released in October, though the free Windows 8.1 update has had a bit more time to simmer — that, and Windows 8, in total, commands more than double the global market share (7.53 percent) as Apple’s OS X 10.8 (3.31 percent), according to NetMarketShare’s figures.

According to Chitika, a number of the Mavericks upgrades came from those already running OS X Mountain Lion, whose adoption rate among OS X users fell six points, compared to last month, ending at a total or 43 percent. The percentage of those using Lion and Snow Leopard fell as well – double the declines previously seen across the past three months, but equaling roughly one-third of the total declines of the Mountain Lion user base.

For more, check out PCMag’s full review of OS X Mavericks and the slideshow above.