Devices may have different requirements regarding a firmware update, depending on their type and available resource (e.g. memory).
Memory constraint devices like sensors often cannot store an additional firmware. These devices install the new firmware while it is transferred to the device. In this specification this is called Direct-Loading (see 18.104.22.168).
Devices with more memory can store a new firmware in a separate memory without installing it which is referred as Cached-Loading in this specification (see 22.214.171.124). In this case the installation is separated from the file transfer and can be done later or with a different Client.
Some devices have two memory partitions for the operating system. One active partition that is used in the boot process and a second alternative fallback partition. These devices install the firmware into the fallback partition and then perform a restart after swapping the active partition. This has an advantage if the device detects an issue with the new firmware: The change can easily be reverted to the old version by switching the partitions again (with another reboot).
Constraint devices like sensors typically do not support a real file system. Devices with more memory often have a file system which can be used to store files like firmware, parameters and backups. This Information Model provides update mechanisms for both types of devices (see 126.96.36.199 for FileSystem based Loading).