Sampling its ad network last week — five months after Mavericks’ release —  Chitika found that 40% of its clients’ page views were coming from Macs running Mavericks. That’s six percentage points better than Mountain Lion ($19.99) reached on the same ad network after nearly 14 months.

It may be a record for a computer OS. Nine months after Windows 8 came out, it still hadn’t achieved 5% penetration (see here).

But 40% pales compared with the upgrade rates on Apple’s smartphones and tablets, where after six months, iOS 7 users were generating more than 80% of Chitika’s iOS Web traffic in the U.S. and Canada.

“That disparity,” Chitika suggests, “is likely at least partially a function of the nature of the desktop marketplace, where computers are typically kept for a longer period of time as compared to mobile devices, and hence may not necessarily be upgrade eligible. Additionally, a larger and much wider range of users in terms of economics, age and other factors regularly browse using desktops and laptops as opposed to smartphones and tablets, which have user bases skewed more tech-savvy as a whole. Finally, unlike on iOS, where users receive a direct prompt to upgrade to the latest OS version, Mac desktop and laptop users were not actively solicited to update to Mavericks.”