So, I’m guessing from the name, El Capitan, that it’s essentially just an update to Yosemite (El Capitan being in Yosemite, of course), rather than a brand new OS: Is that correct?
Yup; much like Lion > Mountain Lion and Leopard > Snow Leopard, it’s mostly about refinement. Worth noting the increasing similarity to iOS –
“The subtle difference in El Capitan is that we’re actually seeing new features come to both iOS and OS X at the same time rather than existing on iOS first and then trickling down to the Mac later. Many of the biggest, most noticeable changes here are the same ones you saw in iOS 9 two weeks ago. The new Split Screen multitasking mode, tweaks to multitouch gestures, changes to services like Spotlight , and overhauled apps like Notes all fall into this category. Others, like System Integrity Protection, are merely iOS-inspired.”
(from Ars Technica review – clicky[/url])