Track track When the disk rotates, if the head stays in one position, each head will draw a circular track on the disk surface. These circular tracks are called tracks. Magnetic surface memory is coated with a magnetic material layer on different shapes of carriers (such as disks, belts, etc.) ). When working, the magnetic head moves at high speed on the magnetic layer, and information is recorded on the magnetic layer. The trajectory of this information is the trajectory. The track of the disk is concentric circles. See the right picture. The track of the tape is a straight line along the length of the tape. These tracks are invisible to the naked eye, because they are just areas magnetized in a special way on the disk, and the information on the disk is stored along such tracks. Adjacent tracks are not adjacent, because the magnetization units are too close, the magnetism will affect each other, and it will also bring difficulties to the head reading and writing. Every file stored on the hard disk can be divided into two parts: the file header and the data area for storing data. The file header is used to record the file name, file attributes, occupied cluster number and other information. The file header is stored in the cluster and mapped in the FAT table (file allocation table). Real data is stored in the data area. The usual deletion is actually to modify the first two codes of the file header. This modification is mapped in the FAT table, marking the file as deleted, and clearing the registration item of the cluster number occupied by the file in the FAT table, which means that the space is released, which is also the reason why the hard disk space usually increases after the file is deleted. The real file content is still stored in the data area and has not been deleted. You need to wait until later to write data and overwrite this data area before you can completely delete the original data. If it is not overwritten by later saved data, it will not be erased from the disk. Partitioning with Fdisk and Formatting with format are similar to deleting files. The former only changes the partition table, while the latter only modifies the FAT table and does not directly delete data from the data area.

According to the principle of file deletion, the only way to completely delete data is to completely overwrite the data area where the deleted file is located. This is the reason why most complete deletion tools are used: write useless data into the data area of the deleted file repeatedly and overwrite it for many times, thus completely deleting the file.

As can be seen from the above, deleting Windows did not completely process files. For very confidential documents, you can use a shredder to handle them.