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Dec 22, 2020
A cluster refers to the minimum disk space that can be allocated to save files. When creating a very small file, such as one byte, it does not occupy only one byte of space on the disk, but the entire "cluster". Cluster is a logical concept used by the operating system, not the physical characteristics of the disk. In order to better manage the disk space and read data from the hard disk more efficiently, the operating system stipulates that only one file can be placed in a cluster, so the space occupied by the file can only be an integer multiple of the cluster. If the actual size of the file is smaller than a cluster, it also occupies a cluster of space. If the actual size of the file is larger than one cluster, according to the logical calculation, the file will occupy two clusters. Even if the file has only 0 bytes, it is not allowed for two files or more than two files to share a cluster, otherwise, it will cause data confusion.
The concept of cluster only applies to the data area. The system depends on different storage media (such as floppy disks, hard disks), hard disks of different capacities, and cluster sizes are different. The size of the cluster can be obtained in the so-called Disk Parameter Block (BPB). Each cluster can include 2, 4, 8, 16, 32, or 64 sectors. The smaller the cluster, the higher the efficiency of storing information.
In the FAT16 file system, each partition has 65,525 clusters at most, and the default cluster size is 32KB; the cluster used in the FAT32 file system is smaller than FAT16, and the default is 4KB.
In Windows 2000/XP, in order to use the compression function to save disk space, two conditions must be followed:
1. The disk partition must be NTFS file system;
2. The size of the cluster in the partition must not exceed 4KB (the default cluster size is 4096 bytes).