Hard Drive Sector and Clusters

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A Sector in the context of computing refers to a small area of a storage device, for example a hard disk drive. For instance, a typical hard disk drive when low-level formatted is split into tracks, sectors and clusters : Tracks are concentric circles around the disk. Sectors are segments of a track. Clusters are a set of sectors. In the example above in fig 1.1 we have only illustrated one track, one sector and one cluster, but you can see where the other tracks, sectors and clusters would reside. A typical hard drive may have 30 or more tracks and 10 or more sectors per track. The size of a cluster will vary depending on the size of the partition.   Bad Sector A bad sector refers to a single sector that has some physical flaw, although a disk can operate with a bad sector, any data that was stored in that sector will be lost, further, no data can be written to that sector. Lost Cluster A lost cluster is a cluster that the operating system has classed as being in use, but actually contains no data. The ScanDisk utility within Windows is designed to search for lost clusters and make them available to the file system again. The Boot Process and the boot sector Boot sector refers to a single sector (normally the first in the active partition) that contains the code to boot the operating system. Before the boot sector is read, the computer's bios will call a small program called an MBR (Master Boot Record) which normally resides in the first record of the first disk. The MBR will query the FAT (File Allocation Table) to establish the primary partition and then pass control over to the boot sector of that partition. The small program stored in the boot sector is then executed and the operating system will begin to load.