GATE CS 1993 Q7.8 — I/O Scheduling

The correct option is B.

Explanation:

The root directory serves as the entry point (the top-most node) of a file system's directory tree. To access any file or subdirectory on a disk, the operating system must first locate and read the root directory.

• Why a fixed location? If the root directory could be placed anywhere arbitrarily, the operating system would not know where to begin searching for it when the disk is mounted. Therefore, it must be placed at a well-known, fixed location on the disk (or its location must be stored at a fixed, predetermined block like the superblock or boot sector).
• Why not only the "system disk" (Options D & E)? Every formatted disk (whether it is a bootable system disk or a non-system data disk) has its own file system and consequently its own root directory. Thus, restricting this rule only to the system disk is incorrect.
• Why not main memory (Option A)? Main memory is volatile. The directory structure must persist across system reboots, so it must reside on the non-volatile disk.

Hence, the root directory of a disk must be placed at a fixed location on the disk.