'''Memory-disk synchronisation''' is a process used in [[computerscomputer]] tos that immediately writes to [[disk storage|disk]] any data queued for writing in volatile memory. Data is often held in this way for efficiency's sake, since writing to disk is a much slower process than writing to [[random access memory|RAM]]. Disk synchronization is needed when the computer is going to be shut down, or occasionally if a particularly important bit of data has just been written.
In [[Unix]]-like systems, a disk synchronization may be requested by any user with the '''sync''' command.
