Just as iOS 9 was built on the foundation laid by iOS 8 for mobile devices, El Capitan improves on the many changes introduced in 2014's Yosemite -- which included new features such as Continuity and a smarter Spotlight search tool. El Capitan adds more polish than features, though there are quite a few of those to explore, as well.
Among the changes made to apps and sprinkled throughout the operating system are better security and a move to Apple's Metal graphics technology (which debuted in iOS) for the system and apps. (Metal replaces OpenGL.) El Capitan also cements in place the adoption of Apple's home-grown programming language, Swift, which allows developers to write apps with smaller latency and more efficient performance.
Like other recent OS X releases, El Capitan is a free download from the App Store. The system requirements are 2GB of RAM and 8GB of available storage. El Capitan will run on Macs that date as far back as mid-2007. (If you're still using a Mac from 2007, though, you should really look into upgrading your hard drive to an SSD for more 2015-like performance.)
But while older Macs can run El Capitan, those systems can't take advantage of all of its features. For instance, although El Capitan is designed to take advantage of both the CPU and the GPU for processing power, only Macs with modern graphics cards -- basically, those released since 2012 -- will be able to utilize this feature. (More on this below.)
The addition of Apple's Metal graphics technology is good news for gamers and other users. Metal is a set of application program interfaces (APIs) designed to supplant OpenGL. The Metal API is actually an Apple-designed combination of OpenGL and OpenCL, which debuted last year in iOS 8. (OpenCL is used to take advantage of every processor on a computer, CPU and graphics card included.)
Metal was designed for efficiency -- a requirement for mobile devices that need long battery life -- and is a much lighter API for graphics compared to OpenGL, letting the graphics card be used more effectively and freeing up the CPU for other tasks. For desktops and laptops, Apple rewrote OS X system software (like the Graphics stack) to take advantage of Metal, resulting in a 50% improvement in rendering performance system-wide and 40% better efficiency (the latter will help laptop users by prolonging battery-charge life).
Apple boasts that El Capitan is 1.4 times faster than previous OS X versions for app launching, twice as fast at switching apps and four times faster at opening PDFs. At the same time, Apple claims a 70% reduction in CPU usage compared to apps written using OpenGL.
Adobe representatives on stage during Apple's September 9th event claimed an eight-fold improvement in using the Adobe After Effects graphics software. Users should find that their systems are more responsive with smoother animations and faster application launches. There is also the promise of future improvements for games and other apps; however, those games and apps must first be rewritten to take advantage of Metal.
Another under-the-hood technology available to developers is Swift 2.0, which is designed to simplify coding (relatively speaking) while making it easy for OS X software to take advantage of the built-in hardware -- such as using the graphics card for data processing when possible. I'm not a programmer, but anything that allows developers to streamline their software is a good thing.
Not everything in El Capitan is behind the scenes and waiting for developers. There are some user-facing features as well.
The first thing astute users may notice is that El Capitan uses a new system font: San Francisco. This font is designed to make text more legible for Apple's high-definition Retina displays. It works as intended, but the difference will probably be overlooked by any but the most fastidious font fanatics.
The updated Finder builds on Yosemite's improvements by applying a new split-screen app mode in addition to the full-screen mode that debuted in Yosemite. The split-screen mode can be enabled in a couple of ways. First, you can drag a Finder window to the top of the menu bar and then drop that window on an existing full-screen app space in Mission Control. Or you can press and hold the green button on an app window -- doing so will make that app fill up half the screen and any open windows display in miniature, letting you select one to fill the other side of the screen.
A clear divider separates the two apps, and each operates independently. The divider can be dragged from side to side to adjust each app's window size. The menu bar at the top of the display automatically changes to accommodate the front-most app, which is normal app behavior Mac users are accustomed to.
It's an elegant solution, one I like a lot, but it's not necessarily obvious to new users. Of course, it's also very similar to Microsoft's implementation in Windows 10.
Managing windows via Mission Control also received attention in El Capitan. Any window dragged to the title bar will activate Mission Control, which lets you move apps to different virtual desktops. Dragging an app window into any existing Space automatically places the window there; dragging the window into a Dpace occupied by a full screen app activates a split-screen view; and dragging a window to the upper right of the display creates a new Space with that window in it.
Spotlight receives some really useful upgrades in El Capitan. Yes, you can move around the search field and results window; they're no longer locked in place at the center of your display. There's also added functionality in search results: Spotlight can check sports data (such as information about favorite athletes or scores, team schedules and standings); it can check weather conditions and forecasts; and when you search for a company's ticker symbol, it can look up stock prices.
The biggest improvement comes in the form of queries, similar to the ones you can ask Siri on iOS. Spotlight now supports natural language search, which generally means Spotlight is as useful as Siri, even though the searches have to be manually typed rather than spoken aloud as you would with an iPhone.
At the iPhone 6S launch event, Craig Federighi, Apple's senior vice president of software engineering, demonstrated this function by typing a search for emails from Phil Schiller that had been ignored. The search results showed unread messages from Schiller. I've used Spotlight to search for documents and videos created during certain time periods, as well as to search for New England Patriot game scores and standings.
There is one minor caveat: When you type a Spotlight search query, you can't press Enter; you have to wait for the results to display after you finish typing them in, even if that takes a while. While this is taking place, there's no obvious indicator that a search is in progress. It's a little annoying, because many users will be inclined to press the Enter key to make sure a search is in progress. That effectively selects the first result and closes the Spotlight search window. That could result in, say, an app launch you didn't intend. Big deal No. Annoying Usually.
For developers, Apple has designed a new API that can display search results of in-app content, which means better search results when developers incorporate this feature in their apps.
Safari gets a number of useful additions this year, but they're mostly tweaks, such as pinned sites, audio muting and -- Apple TV users will welcome this -- built-in AirPlay support for videos.
About that last feature: Videos will now get an additional control icon; tapping the AirPlay icon lets you choose any Apple TV in range so that the video plays through it instead of in the browser window. Previously, this was only possible via third-party plugins, such as ClickToFlash.
While the built-in functionality lacks advanced features found in third-party plugins (ClickToFlash lets you download content instead of simply playing it, for instance), Apple's addition to Safari is stable and works well enough for most people who just want a no-fuss way to stream content to Apple TV. Safari also supports HTML 5 picture-in-picture to enable custom controls for HTML 5 videos and streaming of FairPlay content.
Other Safari changes include:
Mail snags a feature from iOS by gaining more gesture support in the Mail list; the gestures perform different behaviors, depending on whether you swipe left or right with two fingers. These gestures can trigger events like deleting, flagging or marking mail as read (without actually opening the message).
Mail also fixes a problem inherent to full-screen apps that require multiple windows. In Yosemite, when a new message was created while Mail was running in full-screen mode, it wasn't possible to view other messages; they resided in the main window behind the message being composed. In El Capitan, it's now possible to minimize the message window and access other emails and mailboxes; and if you're writing more than one email, they show up in tabs, similar to tabs in the Safari browser.
While iOS 9 offers improvements aimed at predicting what a user will do or what information will be needed, there are now aspects of Mail in El Capitan that offer this, too. For instance, data detectors have been improved, offering suggestions at the top of an email body when they detect phrases in a message that could yield calendar entries, like "Let's go out for dinner at five." This is called suggested events; the same proactive behavior also accounts for potential contacts.
Notes has been updated to bring feature parity with its iOS 9 counterpart, including instant checklist creation, support for inline video and images, and URL snippets with preview. There's a new button that triggers an Attachments view, which organizes attachments from across all of your notes into one area, split into categories like Photos & Video, Sketches, Map Locations, Websites, Audio and Documents.
All of the new Notes features are accessible via the app's toolbar. And beyond the Notes app itself, there is now an extension in the Share button of supported apps that lets you add content from within that app to a new or existing note. Of course, any addition, subtraction or modification to your notes is synced across every device signed in with that Apple ID.
Like Notes, Maps has been improved in El Capitan to create functional parity with iOS 9. Specifically, you can plan routes using public transportation with Transit view, which supports walking directions as well as subway, train, ferry and bus information. Like iOS 9's Maps, Transit data has been surveyed so that Maps shows you the most efficient routes, exits and drop off stops to get to where you're going. As before, you can send those directions to the iPhone from your Mac.
Behind the scenes improvements include security additions, with the most important one in El Capitan called System Integrity Protection (SIP). At its core, System Integrity Protection is a security policy that is applied to every running process. This process protects system files and only allows modifications from the system's installer app and software updates. Code injection and runtime attachments to system binaries are no longer permitted.
What this basically means is that SIP does not allow unauthorized manipulation of important system files, which should help prevent security breaches.
There's a wealth of new features in El Capitan that seem minor -- until you need them. (You can, for instance, find a lost cursor on the screen by shaking your mouse back and forth rapidly, and you'll be able to eventually download extensions to the Photos app for manipulating your images.)
These may not be ground-breaking changes to apps and the operating system, but this collection of small additions makes using El Capitan a little faster, smoother, easier and better. And the under-the-hood technologies lay the groundwork for richer apps down the road. It's these usability iterations found throughout El Capitan that make the biggest difference.
As with any major software upgrade, make sure your apps are supported before moving to El Capitan. If you're hesitant about upgrading, it isn't a bad idea to hold off a while and see if any major bugs are discovered. But because this version was vetted throughout the summer with a public beta program, I'm not expecting any showstoppers now that the final version has arrived.
In a nutshell: El Capitan does what it is designed to -- streamline OS X across the board, making it more efficient to run and flat-out easier to use. It's free, it runs well and I recommend it.