Android 4.3 ran the `fstrim` command while devices were idle to improve filesystem performance.
`fstrim` issues the filesystem TRIM operation, informing flash storage which blocks are no longer needed after files are deleted. The storage controller can then prepare those blocks for future writes, helping maintain performance on NAND-based devices.
Android 4.3, also known as Jelly Bean and released on July 24, 2013, automated this maintenance instead of requiring users to run a command manually. The process was scheduled only under suitable conditions, such as extended idleness and adequate battery charge, to limit disruption and power use.
A common mix-up is confusing `fstrim` with TRIM itself. TRIM is the storage command or operation; `fstrim` is the Linux utility that requests it for a mounted filesystem. `trimfs` is not the command identified in Android 4.3's feature list, while `fsck` and `e2fsck` check filesystem consistency rather than discard unused flash blocks.