What is the smallest allocation unit of a hard disk?

• A. Spinning tracks
• B. Cluster
• C. Disk platters
• D. Slack space

Answer: (B)

In file systems, storage is allocated in fixed-size chunks called clusters. A cluster is the smallest unit the system can allocate to a file, and it is a group of sectors on the disk. Files are stored in one or more clusters, and even a small file will occupy at least one cluster, which means the unused portion of the last cluster becomes slack space. Disk platters and spinning tracks describe physical hardware, not how space is allocated. Slack space refers to that unused portion inside a cluster, not the allocation unit itself. So the smallest allocation unit is the cluster because it’s the smallest chunk the file system can reserve for file data.