This year is shaping up to be a repeat of 2009, when Microsoft and Apple last faced off with rival operating system upgrades.
Three years ago, Microsoft rolled out Windows 7, while Apple launched Snow Leopard, also known as Mac OS X 10.6.
Earlier this month, to the surprise of many observers, Apple shipped a developers preview of Mac OS X 10.8, or Mountain Lion, and said it would ship the final code in "late summer 2012."
Most analysts expect Microsoft to deliver Windows 8 this year, probably in the fourth quarter. The company has slated the release of a so-called "Consumer Preview" version of Windows 8 for Feb. 29.
Ezra Gottheil, an analyst at Technology Business Research, said both vendors' desktop OS upgrades were strongly influenced by their mobile operating systems. "It looks like both have the mobile OS religion," he said.
"Both companies are taking big gambles this year," Gottheil added. "Both recognize that the form factor that's taken off, tablets and smartphones, requires an upgrade from the 25-year-old graphical user interface that's dominated PCs."
While the Redmond, Wash.-based software vendor will retain a traditional desktop in Windows 8, the aggressively promoted Metro interface is the basis for not only the Start screen, but also a new generation of applications that stress touch over mouse and keyboard input.
Mountain Lion is less of a departure for Apple, if only because the company began incorporating elements of iOS into its desktop operating system when it launched Mac OS X 10.7, or Lion, last year. "It seems this is more an incremental upgrade than a major features upgrade," said Gartner analyst Michael Gartenberg.
Mountain Lion will include a wide swath of iOS applications and services, such as Notifications and Reminders, as well as new names for longtime Mac apps, like iCal and Address Book, to match iOS labels.
Both Windows 8 and Mountain Lion will push customers toward their makers' online distribution centers.
Microsoft said that Metro apps will be available only via the Windows Store, although enterprises will be able to offer employees internally created Metro apps that won't be exposed to the public. Traditional 32- and 64-bit Windows applications can be downloaded and installed from any source.
A new feature in Mountain Lion, dubbed "Gatekeeper," lets users decide where to obtain Mac software. The most secure setting only allows installation of programs downloaded from Apple's Mac App Store e-market.
Two other options let Mac owners install any application, no matter its source, or limit installation to software that's either retrieved from the app store or digitally signed by an Apple-approved developer.
While Apple and Microsoft pitch their respective app stores as secure venues that separate the malware chaff from the legitimate software wheat, it's also true that app store sales are a source of revenue for both vendors.
In 2009, Apple beat Microsoft to market, releasing Snow Leopard in late August, about two months before the release of Windows 7.
If Apple comes through with its "late summer" promise for Mountain Lion, it will likely best Microsoft again. And unless Microsoft drastically slashes the price of Windows 8, Apple will probably undercut its rival there again, too.