cluster size : Computer Hardware Buyers’ Glossary

cluster size
When an operating system allocates space on a hard disk, it does it in units called clusters, by default 4096 bytes in Vista. In other OS (Operating System) es the default size depends on the size of the partition. Microsoft sometimes calls it the allocation unit. Even a file of 1 byte takes up at least one entire cluster. On average, each Vista disk file wastes 2048 bytes.

For small files, small cluster sizes mean more efficient use of disk. For large files, big cluster files mean less overhead keeping track of all the pieces. You might put small files on one partition with a small cluster size and large files on another partition with large cluster sizes. The only way I know to change the cluster size is to reformat a partition. This has the unfortunate size effect of erasing all the files. Small cluster sizes mean more RAM (Random Access Memory) is consumed tracking all the pieces of the files.

You can find out the current cluster size of each partition using Boot-It Bare Metal.

For CD (Compact Disk) s, the cluster size is 2352 bytes, called a sector. It is made of 98 bytes of 24 frames.

When a file is deleted, usually its space is recycled without first being wiped. This can cause embarrassment, particularly if you send someone a floppy, USB (Universal Serial Bus) flash drive or hard disk and they have a peek at the erased files, and get to read whatever you had on that floppy/drive before. Similarly, even if you take the precaution of wiping the unused space, sensitive material can live in the unallocated part of the last cluster of each file, called the cluster tips or file tails. You can use Ace utilities to wipe the erased space and cluster tips, a precaution I take before duplicating any floppy for distribution. The problem does not occur with write-once CDs (Compact Disks) and DVDs (Digital Video Discs) since you always use virgin media.

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