_________ maintains the list of free disk blocks in the Unix file system.

Answer: Super block

Explanation: The super block contains filesystem-wide metadata and is responsible for maintaining information about free disk blocks. Depending on the filesystem implementation, this can be a linked free-block list (historical Unix) or a free-block bitmap (modern implementations). The super block also stores other global information such as total number of blocks, block size, and pointers to important filesystem structures.

• I-node: stores metadata for individual files (ownership, permissions, timestamps) and pointers to that file's data blocks; it does not track the global free-block list.

• Boot block: contains bootstrap code for starting the system; not used for managing free disk blocks.

• File allocation table: used by FAT filesystems to track clusters; this is not the mechanism used by Unix filesystems, which rely on the super block and inode structures.