Definition - What does Zero Filling mean?
Zero filling is a method of formatting a hard disk whereby the formatter wipes the disk contents by overwriting them with zeros. Each bit present in the disk is replaced by a zero value, hence the name zero filling. Once the data are overwritten with zeros, the process cannot be undone from the hard drive. Owing to the fact that data are manipulated at the most basic level, this method or way of formatting is called low-level formatting.
Techopedia explains Zero Filling
This technique of formatting is especially useful if the drive has been corrupted or one has to completely erase the contents and install a new operating system along with fresh files for new data. It comes in handy when the system itself is unable to format the disk owing to bad partitioning, virus, corrupt file or unauthorized access. Since each bit has to be rewritten with a zero, it will take a long time to format the disk or drive depending on its size and speed. No tool can retrieve the lost data, which means the loss is permanent. Zero filling can be used to prevent data from being stolen or getting in the wrong hands.