Introduction
Every program you run and every photo, document or database you store must eventually live somewhere permanent — on a hard disk drive (HDD) or a solid-state drive (SSD). The file system is the part of the operating system that turns a raw, featureless sea of disk blocks into the familiar world of files, folders and permissions. Disk scheduling is the sister topic: because a mechanical disk head can only be in one place at a time, the OS must decide in what order to service pending read/write requests so that the disk is used efficiently.
For BCS, Bank IT and IT-officer written exams, this topic is a reliable source of marks. Disk-scheduling problems ("compute total head movement for SSTF") are almost purely numerical and, once you learn the method, are guaranteed marks. File-system questions (allocation methods, inode, FAT, free-space management) are conceptual MCQ favourites. This lesson teaches both from first principles so you can answer any variation.
Learning objectives
- Define a file, its attributes and the operations an OS provides on files.
- Explain how directories are organised (single-level, two-level, tree, acyclic graph).
- Compare the three file-allocation methods: contiguous, linked and indexed, and know FAT and inode structures.
- Describe free-space management techniques (bit vector, linked list, grouping, counting).
- Understand disk physical geometry and compute disk access time = seek + rotational latency + transfer.
- Apply and calculate the six classic disk-scheduling algorithms: FCFS, SSTF, SCAN, C-SCAN, LOOK, C-LOOK.
- Solve numerical problems on total head movement quickly and correctly.