What is System Data on an iPhone’s storage, and how much is normal?

System Data is a changing category of iPhone storage used for supporting files that are not part of the core iOS installation. It can take up a significant share of a device’s space, leaving less room for apps, files and software updates.

The category includes caches, logs, credentials, downloaded fonts, keyboards and Siri voices, as well as iOS updates awaiting installation. Its size varies with a person’s settings and app use, and can range from a few gigabytes to dozens or, in some reports, hundreds. Restarting an iPhone may reduce it temporarily, but deleting unused apps and files is a more lasting way to free space.