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Hard Drive Formatting Explained

June 8th, 2010

how-to-format-hard-drive.jpg“Formatting” is a term that you are likely to hear when discussing or reading about hard drives; it’s also one of the most misunderstood terms among computer users. For example, many users mistakenly believe that formatting a hard drive always erases the data stored on it. In fact, this is often not the case. Formatting is, however, an important part of basic computer maintenance.

Low-Level Formatting

With the first hard drives available to consumers, it was necessary to perform a low-level format on a new hard drive before the drive could be used. A low-level format essentially describes the physical layout of the drive to the computer so the computer can keep track of the locations of saved data. It was necessary to repeat this process occasionally. Otherwise, as the metal platters inside the drive changed shape slightly due to heat, the formatting of the drive would become incorrect, leading to corrupted data. It is no longer necessary — or even possible — to perform a low-level format on modern hard drives.

High-level Formatting

High-level formatting is the process that takes place when today’s computer users format a hard drive. A high-level format creates a new empty file structure on the hard disk, letting the computer know that the drive is empty and ready for data. The type of file structure placed on the drive is defined during the partitioning process. Common partition types include NTFS (newer versions of Windows), FAT32 (older versions of Windows), and HFS (Mac).

Windows Full Format

When a hard drive is formatted in Windows, an option is given to perform either a quick or full format. A full format can take from several minutes up to potentially several hours to complete. During this process, a new file structure is created on the drive. Additionally, the entire physical surface of the hard drive is scanned for sectors that are no longer able to hold data reliably. These are known as “bad sectors.” Bad sectors are remapped to a spare area on the hard drive to prevent data from being corrupted or lost. The sector remapping process is transparent to the end user. If Windows reports bad sectors after performing a full format, the hard drive most likely needs to be replaced.

Windows Quick Format

During a Windows quick format operation, the hard drive is not scanned for bad sectors, and the data on the drive is not erased. Instead, Windows places an empty file structure on the drive which makes the drive appear empty to the operating system. A quick format operation takes seconds to complete.


Some users mistakenly refer to zero-filling a hard drive and low-level formatting synonymously. In fact, zero-filling a drive is not the same as formatting it. When a hard drive is zero-filled, the computer writes junk data across the entire surface of the drive. Zero-filling a hard drive effectively erases it, because the existing data on the drive is overwritten. Zero-filling also makes recovery of the data more difficult. However, zero-filling does not create a new file structure on the drive.

This article was supplied by Gabriel Morgan from Constant Content.

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