Mac OS X 10.6 Snow Leopard install DVDs surface in Apple online store, available for $19.99

In as much as it’s useful to keep operating systems on thumb drives and recovery partitions, there are times where you miss having an emergency DVD on hand.

That being said, this should be useful.

Discovered by French web site MacGeneration and the mighty Mac Observer, Apple’s Mac OS X 10.6 Snow Leopard has returned to Apple’s Online Store as a physical disc purchase after being removed upon the launch of OS X 10.8 Mountain Lion in July.

Snow Leopard, released in August of 2009, was the first Apple operating system to run exclusively on Intel processors. It was also the last version of OS X to include Rosetta, Apple’s translation software that allowed applications written for PowerPC-based Macs to run seamlessly on Intel-powered machines.

Most importantly for owners of older Macs, Snow Leopard represented a crucial transition point for Apple. The Mac App Store, which launched in early January 2011 exclusively on Snow Leopard 10.6.6, inaugurated a new era of digital software distribution. Starting with the launch of OS X 10.7 Lion in July 2011 and continuing with Mountain Lion in July 2012, the primary method for Mac owners to receive new versions of OS X became the Mac App Store (there were indeed other methods of acquiring a new version of OS X, such as the short-lived official USB installer or by making your own, but these were limited options for relatively advanced users).

For users who had already upgraded their eligible Macs to Snow Leopard, the upgrade to Lion or Mountain Lion was simple: purchase and download it from the Mac App Store. But if users were still on OS X 10.5 Leopard or 10.4 Tiger, they would first have to install Snow Leopard to gain access to the Mac App Store, and then purchase and download Lion or Mountain Lion.

As a result, Apple kept OS X Snow Leopard for sale in its online store until the launch of Mountain Lion when, for reasons unknown, the company removed it. Now, thankfully, the Snow Leopard installation DVD is back for US$19.99, and is currently in stock with free shipping.

While it is true that most Mac owners who are eligible to upgrade to Lion or Mountain Lion have already done so (or have at least upgraded to Snow Leopard), for the remaining holdouts who want to try a newer version of OS X, or for current users who want a copy of Snow Leopard in case they ever need to run a PowerPC app via Rosetta, now is the time to snag it while it’s still available.