Scratches on Hard Drive Platters.
Platters facilitate the read-write component of the hard drive; when a hard drive is communicating with the computer data is written to and read from the platters. Scratches impair the drive’s sectors hence these sectors may not be readable.

Causes of Scratched platters
1. Debris/dust causing contact between the read-write heads and the platters
2. Head misalignment which is mostly caused by knocking or kicking the drive. Head misalignment occurs when the drive has undergone a huge physical impact.

How does debris/dust get inside the drive?
1. The breathing hole of most hard drives may let dust particles inside the drive, which will then scratch the platter during the initialization process.
2. Opening the hard drive in a non-clean room environment also introduces debris on the platters.

Data recovery success rate on scratched platters depends on
1. Critical Data Size
Small files have a higher chance of being recovered provided they are not within the scratched area.
Large files however, may not be recoverable since hard drives store different fragments of the file on various places on the platter.
2. Characteristics of the Scratch
Too wide/deep scratches may render the data unrecoverable.

How to prevent scratched platters;
1. Do not open the drive in a non-clean room environment
2. Protect the drive from huge physical impacts that can cause head misalignment.
3. If the drive has clicking noises, do not power it on.

So basically, data recovery chances will depend on how severe the scratches are. if the scratches are severe, it will be impossible to recover the data since every time the heads try to read those sections, they get damaged. However, on less severe scratches, one may partially recover the data mostly in raw format.