Images are “pictures” of the data on a volume, capturing the exact arrangement of bits on a drive. Containers are used in place of partition tables in the APFS filesystem. Disks are the physical manifestation of a drive. In short, disks contain volumes which contain data. APFS, however, resizes volumes within a container on the fly to accommodate data. The size of partitions under those file systems is specified at the time of creation, and changing the size of a partition requires rewriting the partition table. This is distinctly unlike the fixed partitions of other filesystems like ext4, HFS+ or ExFAT. This means the volumes can be flexible, expanding to fit files or shrinking to allow other volumes to grow. The volumes within a given container are allowed to share the space allocated to the container, which has a set maximum size. Within APFS, disks hold containers and containers hold volumes. Containers are distinct from the other items on this list and function a little differently. Specifically, macOS recently introduced containers into its new file system, Apple File System (APFS).

Some filesystems also make use of containers. Open up “Disk Utility” on macOS or Disks in Ubuntu and you’ll see your familiar volume names underneath cryptic-looking disk names. Multiple volumes can be stored on a single disk, and operating systems keep track of what volumes are on what drives. When you mount a storage device and its icon appears in your file browser, you’re seeing the volume. While partitions and volumes are coterminal, a volume has a name and file system in addition to a size. VolumeĪ volume is the part of the disk that you interact with as a user. A partition can be resized, but it requires re-writing the disk’s partition table and possibly erasing data. Instead, a partition is just a part of a disk with a specific size, which is set at the time of creation. It doesn’t necessarily contain a file system, and it might not be formatted to store data. Even system programs like macOS’ Disk Utility don’t distinguish between the unformatted partition and the formatted volume. But if we want to get precise, a “partition” is a chunk of a disk. In fact, the two terms are used almost interchangeably.

Mac disk image from drive