Snow Leopard, which debuted in 2009, does not support iCloud -- only OS X 10.7, or Lion, does -- but with the free upgrade to the former, users will have to pay only one upgrade fee, the $29.99 for Lion, to use the service.
Lion is available through the .
The offer only makes sense for Mac users running OS X 10.5, aka Leopard, or earlier, on systems powered by Intel processors: Neither Snow Leopard or Lion support older PowerPC processor-equipped Macs.
About 18% of all Mac users, or fewer than one-in-six, ran Leopard or one of its predecessors last month, according to Internet metrics company Net Applications.
, a move it announced last year.