What Causes a Corrupt File?
Corrupt files can be caused by a number of system errors. Normally, when a file becomes corrupt, it cannot be accessed or some data in the file is lost. In some cases data from a corrupt file is retrievable, such as in some Microsoft Office programs which have a "recovery mode" for automatically saved data.
Sectors are divisions of a hard disk. When a user tries to save a file, the computer searches for a sector on the hard disk to save the data. If the computer saves a file to a "bad sector," the file is likely to become corrupt or inaccessible. Bad sectors can be caused by physical damage (i.e., the hard disk losing magnetism and hence its ability to store data) or bad parity checks on the disk. A computer does not know which sectors are bad or unstable, so the user must scan hard disks (such as the C Drive) to check for bad sectors. This can be done by right-clicking on the drive from "My Computer," selecting "Properties," "Tools" and selecting "Check Now" under the heading "Error-checking."
Cross-Linked Files or Lost Clusters
In computer systems, a "cluster" is the smallest amount of disk space needed to store a file. Files are allocated individual clusters, which can range from one sector (512 bytes) to 128 sectors (64 kilobytes). A cross-linked file occurs when two or more files have been allocated the same cluster, which will corrupt all files saved to the same cluster. Lost clusters may also cause corrupt files; when a file is deleted from the computer's directory listing, but the File Allocation Table (FAT) still shows clusters allocated to that file, the clusters become "lost" and data which is saved to this cluster will show as "cross-linked," even if the directory listing has already been deleted.
Infected Files and Viruses
Viruses can delete files, infect the computer registry, change volume labels, mark sectors as bad on the drive, mark clusters as bad in the FAT, create cross-linked files or create new partitions on the disk drive. A virus can easily change how files are saved and read on a computer, causing corrupt files to occur even if no problem exists with a hard drive. Viruses can, for example, mark sectors as bad when they are functioning normally, and cause all files to become corrupt or inaccessible for the user in that sector.
System crashes can be caused by various factors on a computer system. Logical crashes (i.e., complete shut down, or the "Blue Screen of Death" for Windows users) occur when programs use conflicting memory, or when new hardware is corrupt. Programs are normally allocated memory from the system and cannot share a portion of memory; if one program accesses another program's allocated memory, a crash may occur. If programs using kernel memory (trusted programs, such as the operating aystem or hardware drivers) access another kernel program's memory, a system crash/shutdown will occur. In both cases, if a file is being saved, accessed or sometimes open, the file may become corrupt from a sudden shutdown.
References & Resources
- Microsoft TechNet: Recovering Data From Corrupted Files
- Data Recovery: Bad Sectors
- Microsoft Support: Errors Caused by Cross-Linked Files or Lost Clusters
- NTFS: File Storage Hard Drives and Disk Organization
- Computer Hope: Computer Virus Information and Help
- Network World: How to Solve Windows System Crashes in Minutes