Secondary Storage Management
Secondary storage (disk) is the persistent memory, i.e., it endures system failures (we hope).
Low-level OS routines are typically responsible for low-level disk function, such as scheduling of disk operations, head movement, error handling, etc.
These routines may also be responsible for managing space on the disk....
BUT, the line between this and the file system is very fuzzy...space management functions may belong in the file system.