A cluster may refer to any of the following:
1. When referring to a hard drive, a cluster or file allocation unit is the smallest managed section of a hard drive that holds a file. The size of a hard drive cluster can vary by operating system and size of hard drive.
Because each file and directory takes up one or more clusters depending on their size, earlier versions of FAT had the potential of wasting hard drive space. For example, if the cluster size was 8 k and a 2 k file is stored on the computer, 6 k of that cluster will go to waste.
This issue is reduced with new versions of FAT such as FAT32.
2. A cluster or hardware clustering defines a group of computers or servers that share the work. A cluster makes one big computer instead of multiple smaller computers and allows for additional hardware to be added as the workload increases. The picture is an example of cluster of rack mountable computers at the NCSA/University of Illinois.