This article originally appeared in TidBITS on 2016-06-24 at 8:01 a.m.
The permanent URL for this article is: http://tidbits.com/article/16584
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What Apple’s Forthcoming APFS File System Means to You

by Michael E. Cohen

Among the tidbits Apple revealed to its developer audience at the recently completed Worldwide Developers Conference was a new file system for the whole range of its products (see “macOS 10.12 Sierra to Succeed OS X 10.11 El Capitan [1],” 13 June 2016). Dubbed “APFS” (an acronym that Apple doesn’t completely spell out even in its developer documentation), the file system is meant to replace HFS+, the file system that in turn replaced 1985’s HFS (Hierarchical File System) in 1998. (HFS+ has received numerous updates since 1998, so don’t get the impression that it’s completely obsolete.) Apple released a developer preview of APFS with macOS 10.12 Sierra, and the company says APFS will become the default file system in all of its operating systems — macOS, iOS, watchOS, and tvOS — by late 2017.

Changing the default file system for an operating system is a big deal, since the file system is responsible for keeping track of all of the data on the device. But what does such a change mean for users?

The Finder Is Not the File System -- Unless you’re one of those rare individuals who lives on the Terminal command line and who can type ls -la faster than you can double-click a folder icon, the Finder, along with the Mac’s Open and Save File dialogs, is normally how you see what’s on your Mac and how you navigate among your files and folders. This won’t change when APFS takes over from HFS+.

That’s because the Finder is a client of the file system. The Finder shows you a view of the items you have stored on your Mac and lets you arrange files and folders in a manner that works for you. The Finder, along with its folder and file icons, has been on the Mac since before even HFS came around, and has worked more or less the same from the user’s point of view since the first Mac came out of a bag and said “Hello” back in 1984.

The file system works behind the scenes, providing information to the Finder and to applications about the files and directories that are stored in some fashion on a device connected to your Mac — whether in magnetic fields recorded on a spinning platter or charged cells in a solid-state device. The file system keeps track of how much storage capacity files take up on the device, where on the device the data that make up the files are stored, and all sorts of metadata about those files, such as their names, when they were created and last changed, which users are allowed to open them, and a great deal of other stuff.

The Finder is thus an intermediary. Its job is to present us ordinary mortals with an easily understandable view of the data that the file system actually manages, and to instruct the file system about what you want to do with that data. As long as the Finder can communicate adequately with a file system to enable that view and pass along your instructions, the actual file system being used on a storage device doesn’t matter much.

In fact, if you have ever used a thumb drive or an SD card with your Mac, you may have already seen the Finder working with a file system other than HFS+. Most thumb drives and SD cards come formatted for Windows computers and use the FAT (File Allocation Table) file system, and yet you can still see and manipulate the files and folders on them with the Finder.

APFS is designed to understand nearly all of the same instructions and information requests that the Finder, or any other Mac application, issues regarding storage devices managed by HFS+. You’ll still be able to move files, rename files, copy files, open files, delete files, tag files, and so on just as you always did.

But You Will Notice Some Differences -- However, APFS does provide some benefits over HFS+, and they’re significant enough that you will likely notice them in action.

HFS+ came along well before large storage devices containing gigabytes, let alone terabytes, were common, well before flash memory was commonly used for file storage, well before file encryption was something that ordinary users cared about, and well before Mac OS was replaced with OS X and its virtual-memory-enabled multi-tasking capabilities.

Support for large data volumes, encryption, flash drives, and virtual memory was more or less bolted onto HFS+ instead of being integrated into it. APFS has that support, and more, built in and will thus have an impact on your experience as a user.

Transition to APFS -- Apple intends the transition to be as painless as possible. When you buy a new Mac once APFS is the default file system, you should have no transition hassle at all: Setup Assistant should move your data from your old Mac to the new one pretty much as it has all along. And, since macOS will continue to support HFS+ as well as APFS (just as it supports other file systems), you’ll be able to mount and use older HFS+-formatted external drives with no problems.

Apple also plans to provide an in-place APFS migration utility for users who upgrade older Macs to a macOS version that uses APFS as its default. Most likely, the migration process will take some time (minutes or hours) to convert an existing HFS+ device to APFS, but Apple’s goal is to make the process as simple and as safe as possible.

Let’s all hope Apple meets that goal: APFS is a big deal, offering notable performance, space-saving, and security benefits to users while promising to work its magic unobtrusively behind the scenes — as any good file system should.

[1]: http://tidbits.com/article/16569