Apple has re-posted / modified one of its Support articles outlining the differences between updating your software, and performing a major upgrade. Last modified on September 02, 2009, article HT1444 summarizes its contents saying, “Find out the differences between an Apple software update and an upgrade.”

Products affected include Mac OS X 10.4, Mac OS X 10.3, Mac OS X 10.2, Mac OS X 10.1, Mac OS X 10.0, Mac OS X 10.5, as well as the latest revision to the Mac OS, Mac OS X 10.6 aka Snow Leopard.

Apple begins by revealing what an Upgrade is. According to the Mac maker, “an Apple ‘software upgrade’ means a major, standalone version of a software product. Such products are usually something you purchase. They are shipped in a box or shrink-wrapped package. Mac OS X upgrades are sometimes also called ‘reference releases.’ For example,” Apple pinpoints, “Mac OS X v10.6 is an upgrade product available from an Apple reseller, Apple Retail store, or the Apple Online Store.”

An Update, on the other hand, is something a tad less significant, but important nonetheless (in most cases). “A ‘software update’ updates a major (reference release) version of software, but does not upgrade it to the next major version (if one exists),” the Mac maker explains. “Software updates are made available via download from the Software Update application in Mac OS X and typically provide fixes that enhance the stability, compatibility and security of your Mac.” An example is provided here as well. Those who’ve updated their systems to Mac OS X v10.5.8 from any prior version of Mac OS X v10.5 have performed what Apple calls an “Update.”

For an even better understanding of the terms “upgrade” and “update,” Apple posts some key differences between the two. As such, Apple says, “A software update is usually downloadable [while] a software upgrade usually is not.”

Moreover, “A software upgrade usually increments the first ‘dot’ number of a product (for example Mac OS X v10.6, Mac OS X v10.5); a downloadable software update usually increments second ‘dot’ number (for example, Mac OS X v10.4.11, Mac OS X v10.5.8),” the Support document reveals.

Want an even shorter explanation? At the beginning of August, most Mac owners running 10.5.x (Leopard) Updated to Mac OS X 10.5.8. On, or after August 28, those same people bought Mac OS X 10.6 (Snow Leopard) on to perform an Upgrade.