Moreover, many third parties have stopped releasing software updates compatible with older operating systems.
For example, the latest versions of Chrome and Firefox won't run on anything older than Mavericks.
Before you upgrade, be sure to read our How to Prepare Your Mac for mac OS Sierra article for additional advice.
If your Mac can't run Sierra, there's still a decent chance that it can run the previous version of mac OS, El Capitan, which may continue to receive security updates from Apple for another year or two.
An alternative solution for upgrading a compatible Mac from Snow Leopard to Sierra is to first upgrade to your choice of Lion through El Capitan (if you happen to have a bootable installer from one of those versions of mac OS handy, or if you're able to download one from the Purchased section of the App Store and use Disk Maker X to create a bootable installer), and then do a second upgrade from that mac OS version to Sierra.
Taking this upgrade path will allow you to preserve your hard drive's contents.
Certain older Mac models are still limited to Lion (10.7), which has not been getting security patches since Yosemite was released two years ago.
Some early Intel Macs released in 2006 are stuck with Snow Leopard (10.6), which hasn't received security updates since the release of Mavericks three years ago.
While Apple boasts about the extremely high percentage of i Phone, i Pad, and i Pod touch devices that are rapidly upgraded to each major new version of i OS, such is not necessarily the case with Macs and OS X.The only security-related update that Apple is continuing to release for Snow Leopard through Mavericks is the XProtect "[un]Safe Downloads List," which blocks a handful of malicious downloads (although signatures are often added too late to be of much use) and prevents Flash and Java content from running in your browser—if your plug-ins are too outdated and likely to be exploited.It's important to note that XProtect updates, while better than nothing, are by themselves insufficient to adequately protect your Mac.If your Mac isn't new enough to run Sierra or even El Capitan, then, unfortunately, it will no longer receive much support from Apple.Sadly, Apple doesn't give users any direct warning when their operating system or Mac is no longer supported.