Mac OS (Classical and X):
-Comes out with a new version every YEAR.
-Compatible with only 10% of all computers.
-Cost: about $129
(price chceck on 13 of Feb, 2006 from: http://store.apple.com/1-800-MY-APPLE/WebObjects/AppleStore?productLearnMore=MA190Z/A)
-Comes out every 2 or 3 years with a new release.
-Operates 90% of all computers.
(price as of Feb 13, 2006; from: http://www.pricegrabber.com/search_getprod.php/masterid=4197929/skd=1/search=buy+microsoft+windows)