What Is an Alias in OS X El Capitan?
An alias is a tiny file that automatically opens the file, folder, disk, or network volume that it represents. Although an alias is technically an icon, it’s different from other icons; it actually does nothing but open a different icon when you double-click. Put another way, aliases are organizational tools that let you store an icon in more than one place without creating multiple copies of the file.
An alias is very different from a duplicated file. For example, the iTunes application uses around 340 megabytes (MB) of hard drive space. If you were to duplicate iTunes, you’d have two files on your hard disk, each requiring around 340MB of disk space.
An alias of iTunes, on the other hand, looks just like the original iTunes icon and opens iTunes when you double-click it but uses less than 2MB of hard disk space. So try placing aliases of programs and files you use most often in convenient places such as the Desktop or a folder in your Home folder.
In effect, Microsoft stole the alias feature from Apple. (If you’ve used Windows, you may know aliases as shortcuts.) But what else is new? And for what it’s worth, the Mac’s aliases don’t usually break when you move or rename the original file; Windows shortcuts have been known to do so (although it’s less frequent in Windows 10 than in Windows XP).
Aliases also open any file or folder (or application) on any hard drive from anywhere else on any hard drive — which is a very good trick. But there are other reasons why aliases are awesome:
Convenience: Aliases enable you to make items appear to be in more than one place, which on many occasions is exactly what you want to do. For example, keep an alias of your word-processor program on your Desktop and another in your Documents folder for quick access. Aliases enable you to open your word processor right away without having to navigate into the depths of your Applications folder every time you need it.
While you’re at it, you might want to put an icon for your word processor in both the Dock and the Sidebar to make it even easier to open your word processor without a lot of clicking.
Flexibility and organization: You can create aliases and store them anywhere on your hard drive to represent the same document in several different folders. This is a great help when you need to file a document that can logically be stored in any of several folders. If you write a memo to Fred Smith about the Smythe Marketing Campaign to be executed in the fourth quarter, which folder does the document belong in? Smith? Smythe? Marketing? Memos? 4th Quarter? Correct answer: With aliases, it can go in every folder, if you like. Then you can find the memo wherever you look instead of guessing which folder you filed it in.
Integrity: Some programs must remain in the same folder as their supporting files and folders. Some programs, for example, won’t function properly unless they’re in the same folder as their dictionaries, thesauruses, data files (for games), templates, and so on. Thus, you can’t put the actual icon for such programs on the Desktop without impairing their functionality. An alias lets you access a program like that from anywhere on your hard drive. (And it’s probably best to leave all your apps in the Applications folder, where they belong.)
El Capitan’s speedy Spotlight search mechanism along with tools like Launchpad and Mission Control, as well as the Sidebar’s All My Files item, let you find pretty much any file on your disk in seconds.