Details Emerge on Apple’s New File System APFS - What Does it All Mean?

| Analysis

A very important and geeky technology that Apple has been working on surfaced after the WWDC keynote, namely that Apple has been working on a new file system for the Mac and other Apple devices. It was probably too geeky to make the cut for a keynote broadcast live, but it's still incredibly important. Here's the background and what we know about APFS.

What is a File System?

A file system is method used by a computer to store and retrieve data. A simple way of thinking about it is an old-fashioned phone book. A phone book stores names, addresses and phone numbers alphabetically by name. When we look up a name, we know how to scan alphabetically, read across what we found, and retrieve the phone number on the same line.

Similarly, a computer files system is a set of protocols and code that specifies how data (and metadata) is stored, found, retrieved. In simple terms, things like multiple write contentions, buffering and file integrity, and file size and number limits are set.


Computer file systems have evolved over the years to meet the need of ever advancing hardware. When hardware and processors were slow, it didn't make sense, nor was it possible, to design very advanced file systems. And, so, periodically we go through a technology convulsion as the vendor designs a more capable file system and we (carefully) migrate with it.

We've gone from floppy disks to hard disks to SSDs in the lifetime of the Mac, and the amount of user data has expanded by many orders of magnitude. File systems are revised, hopefully with backwards compatibility, so tha users can continue to access older devices while dealing with terabytes and perhaps petabytes of data.

The file system Apple has been using since 1998 for both the Classic Mac OS as well as the evolution of Mac OS X, OS X, and now macOS is called HFS+. It was suitable for the Classic Mac OS in the 1990s and perhaps barely suitable for a UNIX file system, BSD, that Apple called Mac OS X back in 2001. But then, it generally worked well, Apple had control of it, and it could be designed at will to meet the UI and UX needs of Apple's customers. Today, iOS, tvOS and watchOS have inherited HFS+.

Over the years, it became clear that HFS+ was not a file system that could take the Mac and inheritors of HFS+ into the future. Apple experimented briefly in 2009 with Sun's ZFS file system, but there were issues that prevented its deployment. That's beyond the scope of this discussion.

Other events that have driven Apple's quest for a new file system, especially on the Mac, have been the need for more robust security, the nagging problem of how Time Machine volumes are managed (and encrypted) and the widespread use of SSDs/Flash storage, especially as boot drives in Macs today.

Page 2: Criticism of HFS+, APFS to the Rescue, Release Plans

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I am very excited about APFS. Probably more than anything else in the Keynote. Once absurdly geeky question.

I understand how a file system is mapped out on a rotating platter drive. Physically it’s deviced into cylinders and sectors and the file you want is in cylendar xxxxxx sector yyyy-zzzz. But how do they keep a file system straight in an SSD? This is all chips and electronics. Is it by memory address? For that matter if I have an SSD that’s HFS+ how does it change to APFS? Is reformatting an SSD just a matter of telling the memory itself to forget and then giving the controller a new map? That would be quick. I haven’t yet wrapped my head around how drive management works when you don’t have a circular spinning playing field to work with.

Hey, maybe that’s an idea for an article.


The worst ever is MS-DOS.  Even the path separators are backwards. smile

As for APFS…. Apple has their work cut out.  Hopefully they can get it right.


Um, didn’t Apple start out with a file system that they called MFS ?
Then they upgraded to HFS…........

John Martellaro

furbies:  That goes WAY back, but you’re right!

Scott B in DC

Two other features that would make APFS a better filesystem (besides the support for sparse files, which I like) is the support for native file (hard) links and logical volume grouping. Yes, I know LVG is a RAID function, but having used IBM’s version of LVG under AIX you can throw a file system across several non-connected disk volumes. If it is attached as a disk, even using something like ISCSI, you can create LVG volumes.

Think about having a bunch of disks attached via USB that you can group together or even networked from other computers.

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