How or Why do Files Become Corrupt?

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Disk risk

This is mostly about the hard disk in your computer, but can apply to any data-storage medium. It’s not uncommon for a hard disk to develop or even come with a bad sector – an area on the actual medium that is somehow damaged.

Think of a bad sector as a typo in something you’re reading1 – but it can’t be fixed.

Sometimes it’s small or benign, and you can easily figure out what was intended. Other times, the typo is bad, there’s no way to understand what was said. In the worst case, the typo – perhaps even a tiny one – will render some key information or plot point completely unintelligible.

Where bad sectors come from

Bad sectors develop for a number of different reasons.

Magnetic media may come with a subtle flaw or a “thin spot” that simply wears out over time. Another common cause is motion – a disk drive getting banged around while it’s in use, and the read/write mechanism perhaps ever so slightly touching the magnetic material, which should never happen, and scratching it. This is one of the reasons that the more rugged laptop drives are also somewhat slower: the mechanisms are often built more solidly with motion in mind so as to minimize this risk.

Optical media like CDs and DVDs degrade over time.

Flash memory, as used in thumbdrives and SSDs, is known to literally wear out the more it’s written to.

But regardless of these and other causes, it can and does happen …

… and data loss is the typical result.

Data corruption

Corruption is nothing more than data that’s supposed to be one thing erroneously getting changed to something it shouldn’t be. For example, data that used to be:

The quick brown fox jumps over the lazy dog.

might suddenly become:

The quick br�-t�?h�Z�O1E���-�Ca �f�E??IG�Gq+

Now, it’s one thing if the text you’re reading is suddenly garbled like that, but if that’s your financial data, or one of your installed programs – or even Windows itself – the results can be disastrous.

How corruption appears

Exactly how data corruption manifests varies dramatically based on exactly what’s been harmed and to what extent.

• You might never notice, because the bad sector is on some unused portion of your hard disk, or in part of a file you never or rarely use, or where the corruption is actually benign.
• In some relatively benign cases, you might get a “read error” or a “CRC error”, as the operating system detects that some form of data corruption had occurred.
• You might open a document to find its content scrambled.
• In more complex document formats (Microsoft Office documents are a good example), the program might not be able to open the document, due to corruption within.
• If the corruption happens within the file that contains a computer program (usually an EXE or DLL file), the program might not run at all, might crash when you run it, or might crash at some point when you access a certain feature that uses the instructions that have been damaged.
• If the corruption happens within the file system information – perhaps the information about what files are stored on the disk – files can disappear completely.
• If the corruption happens within the files that comprise Windows itself, Windows can crash or fail to boot.
• If the corruption happens within the master boot record, partition information, or other key areas of the hard disk, the entire disk may suddenly appear unformatted or empty.

Prevention

So, how do you prevent corruption?

Easy: you can’t.

You cannot prevent a hard drive from developing bad sectors or failing. It happens. The best you can do is prepare.

What you can prevent is data loss.

The real “solution” is to know that someday, when you least expect it (and probably when it’ll be most inconvenient), it will happen.

The real solution is to be prepared with a complete and recent backup if your computer’s hard disk, your data, and whatever else is stored on any media that might fail (and by that, I mean all media). That way, when – not if – failure happens, you can replace the failed component (usually the drive), restore your files, and get on with your life as if nothing major happened.