Disk formatting facts for kids

Disk formatting is like preparing a blank notebook so you can start writing in it. It's the process of getting a data storage device ready to be used for the first time. This includes things like hard disk drives, solid-state drives, floppy disks, memory cards, and USB flash drives.

Sometimes, formatting also creates one or more new file systems. Think of a file system as the way your computer organizes files on the disk, like how you might organize your notes with different sections in a notebook. The whole process often has three main parts: "low-level formatting," "partitioning," and "high-level formatting." When you "format" a disk, it usually means you're doing all these steps to make it ready to store your files. Some formatting tools let you choose a "quick format" (which doesn't completely erase old data) or a "long format" (which does erase everything).

Generally, formatting a disk doesn't completely remove all the old data. Most of it might still be there and could be recovered with special tools. To truly erase data, you need special tools that overwrite everything on the disk.

How Disk Formatting Changed

In the past, disk drives stored data in small sections called "blocks." A block is the smallest amount of storage a computer can read or write at one time. Early disks had fixed block sizes, meaning every block was the same size. Later, some disks allowed different block sizes on the same track, but this became less common by the 1990s.

Today, modern hard drives like Serial attached SCSI (SAS) and Serial ATA (SATA) drives use fixed-size blocks. For many years, these blocks were 512 bytes long. But starting around 2009, most hard drive makers began using a new system called Advanced Format, which uses larger blocks of 4096 bytes.

Floppy disks and Optical discs (like CDs and DVDs) usually use fixed block sizes. These sizes often depended on the computer's OS and how it worked with the disk controller.

Steps to Format a Disk

Getting a disk ready for your computer and its programs usually involves three main steps:

Low-Level Formatting

Low-level formatting is the most basic step, closest to the disk's hardware. It marks the disk's surface with special markers that show where each recording block (called a sector) begins. It also adds other important information, like CRC codes, which help the disk controller check for errors when reading or writing data.

This step creates the permanent foundation of the disk. It's almost always done at the factory where the disk is made. You usually can't do this yourself on modern hard drives.

Floppy Disk Low-Level Formatting

For floppy disks, low-level formatting was often done by the disk drive's controller. For example, a standard 1.44 MB floppy disk would be low-level formatted with 18 sectors (each 512 bytes) on each of its 160 tracks. This gives it 1,474,560 bytes of storage.

The actual physical sectors are a bit larger than 512 bytes because they include extra information like an identifier and error-checking bytes. These extra bytes aren't usually counted in the total storage capacity.

Hard Disk Low-Level Formatting (Old Days)

Before the 1990s, hard drives often had a separate disk controller that decided how data was stored. Users could sometimes perform low-level formatting on these older hard drives. This involved dividing each track into blocks for user data and control information. By the mid-1980s, 512 bytes per block became a standard.

On older computers, low-level formatting was usually done using special tools or parts of the operating system.

Why Users Can't Low-Level Format Modern Disks

Since the late 1980s, hard drives started coming from the factory already low-level formatted. The way hard drives connect to computers also changed. Modern drives are "intelligent" and handle their own low-level formatting internally. Because of this, you can't perform a low-level format on a modern hard drive yourself.

Modern Disks: Reinitialization

Since true low-level formatting isn't possible for users on modern hard drives, the term "reinitialization" is used. This means returning a disk to a factory-like state: no data, no partitions, and all storage blocks ready to be used.

Filling the Disk with Data

If a disk's built-in reinitialization function isn't available, you can fill the entire disk with data. A common way is to fill it with "zeros." This process can take many hours. It erases all files and file systems.

Filling a drive with zeros is not a secure way to prepare a drive for encrypted files. For sensitive data, more advanced methods are needed to make sure the old data is truly unrecoverable.

Disk Partitioning

Partitioning is the process of dividing a disk into one or more separate sections. Each section acts like its own separate storage device to the computer. Sometimes, partitioning also sets up the disk so an operating system can start from it.

On operating systems like MS-DOS, Microsoft Windows, Linux, and macOS, this is usually done with a partition editor program. Examples include fdisk or GNU Parted. These systems can have multiple partitions on one physical disk.

Floppy disks are not partitioned. However, they still need some basic information to be used by the operating system.

High-Level Formatting

High-level formatting is the process of setting up an empty file system on a disk partition. For PCs, this also includes installing a boot sector, which helps the computer start up. This step is often very fast and is sometimes called a "quick format."

When you do a "long" or full format, the disk might also be scanned for defects, which can take a lot of time.

For floppy disks, both high-level and low-level formatting were often done at the same time by the formatting software. Since the 1990s, most floppy disks came pre-formatted from the factory.

Reformatting a Disk

Reformatting means performing a high-level format on a disk that already has data on it. The main goal of reformatting is to free up space on the disk for new data. What actually happens to the old data depends on the operating system. Many quick format tools don't completely erase everything. To truly "erase" all data, you need to overwrite every part of the disk.

Reformatting often means you'll reinstall the operating system and all other software afterward. People might "reformat" a computer to fix problems or start fresh. However, if a drive only contains user data, reformatting it doesn't require reinstalling the operating system.

Formatting Tools

DOS, OS/2, and Windows

In MS-DOS, PC DOS, OS/2, and Microsoft Windows, you can format a disk using the `format` command. This program usually asks you to confirm before it starts to prevent you from accidentally deleting data.

In Windows Vista and newer versions, a non-quick format will overwrite the data as it formats. This was not the case in Windows XP and older versions.

Unix-like Operating Systems

On systems like Linux and macOS, high-level formatting is usually done with the `mkfs` command. This command often works with other specific commands for different file systems.

Some Unix-like operating systems also have easier-to-use tools for formatting and partitioning disks. Examples include GNU Parted and the Disk Utility application on Mac OS X.

Can You Get Data Back from a Formatted Disk?

Just like when you delete a file, data on a disk is not fully erased during every high-level format. Instead, the space where the data was is simply marked as "available." The old data stays there until new data is written over it.

If you format a disk with a different file system, some old data might be overwritten that wouldn't have been otherwise. However, it's still possible that much of the old data remains.

To truly prevent sensitive data from being recovered, the data must be completely overwritten. This can be done with special tools or by using a "long" format option if available.

It's debated whether one pass of filling a disk with zeros is enough to destroy sensitive data on very old magnetic storage. However, for modern drives, one pass of zero-fill is generally considered enough to prevent data recovery by common methods. The "Secure Erase" option built into many modern hard drives is also considered reliable.

Degaussing (using a strong magnetic field) is another way to destroy data, but it usually makes the drive unusable afterward.

See also

• Data erasure
• Data recovery
• Data remanence
• Drive mapping
• Comparison of file systems