FIND OUT ABOUT APFS
Using High Sierra’s new storage format
Normally you don’t have to concern yourself with the file system that’s used to store data on drives, whether internal
or external. In fact, the only time you may ever have thought about this in the past is when setting up new storage, such as an external hard drive or a USB flash drive.
In the past, the choice was easy: you would use Mac OS Extended (also known as Hierarchical File System Plus, or HFS+) if a drive would only be used with Macs, or FAT or ExFAT if it’ll also be used with a Windows PC.
You have a new choice in High Sierra: Apple Filing System (APFS). The reason is Mac OS Extended’s origins lie all the way back in the 80s, when spinning magnetic disks were the norm; Apple says APFS is optimised for solid-state drives, and that this new option provides improved file system fundamentals, strong encryption, snapshots, and other things you don’t really need to think about day-to-day.
When you install High Sierra on your Mac’s internal drive, and that drive is made up purely of flash storage, then it’s converted to APFS. You can’t opt out of this. If it’s a hard drive or Fusion Drive, no conversion takes place; that’s intentional, but worth knowing in case you heard about APFS already and expected a switch.
APFS and External storage
Regardless of your Mac’s internal drive, APFS is something to consider when formatting drives you’ll use with other Macs or PCs. To use a drive with a PC, use FAT as its format if the capacity is up to 32GB, or ExFAT if it’s larger than that.
To use an SSD or flash drive with a Mac running a system older than High Sierra, avoid APFS; older systems can neither write to nor read from it, so stick with Mac OS Extended. If all your Macs are on High Sierra, APFS is preferable, but consider the chance you’ll use the drive to pass files to someone on an older system.
You can erase or convert a hard drive to APFS, but given it’s intended for flash storage and High Sierra doesn’t convert hard drives automatically, sticking with Mac OS Extended is the sensible option. We’ve got a couple of guides here to explain how to work with APFS.