How Computers Work · Files & Storage Deep Dive · Lesson 4 of 5

Formatting, Encryption and Wiping

Format a drive, guard your recovery key and wipe a computer before you sell it.

What formatting does, quick or full

Formatting a drive means setting it up with a fresh, empty file system. It is like throwing out a library's whole catalog and starting a new, blank one. After formatting, the drive looks empty and is ready for new files.

People format drives to change the file system, like turning a FAT32 USB stick into exFAT. They also format to clear a drive for a new use.

On Windows, open File Explorer, right-click the drive and choose Format. On a Mac, open the Disk Utility app, pick the drive and click Erase.

Formatting erases everything on the drive, so check twice that you picked the right one. Windows won't let you format the drive it is running from, but it will format a USB stick in seconds.

The Windows Format box has a Quick Format checkbox, and it makes a big difference:

• Quick format writes a new, empty file system and stops. It takes seconds. Like a normal delete, old data on a hard drive is mostly still there, and recovery tools may find it.
• Full format also checks the whole drive for bad spots and, on modern Windows, writes zeros over every part of it. It can take hours on a big hard drive, but the old files are overwritten.

A quick format is fine for a USB stick you keep using yourself. When a drive is leaving your hands, a quick format alone is not enough.

SSDs are different again. For an SSD, the safest tools are encryption and the maker's own secure erase, which you'll meet next.

Recovery keys, and wiping before you sell

If your drive uses BitLocker or Device Encryption, keep one thing safe: the recovery key.

A recovery key is a 48-digit number that unlocks an encrypted drive when the normal sign-in can't. Windows may ask for it after a hardware change, a firmware update or some repairs. Without it, nobody can open the files. Not you, and not a repair shop.

On many home computers, Windows saves the key to the Microsoft account you sign in with. You can see it by signing in at aka.ms/myrecoverykey from another device. Check today that it is there. You can also print it, and keep the printout away from the computer.

When you sell or give away a computer, you want your files gone for good. Windows 11 has a built-in way:

1. Back up anything you want to keep.
2. Open Settings > System > Recovery and click Reset PC.
3. Choose Remove everything.
4. Under Change settings, turn on Clean data.

Clean data removes your files and also cleans the drive. It can take hours on a big hard drive, so keep the computer plugged in. Microsoft recommends it when you donate, recycle or sell a PC.

Many drive makers also offer a free secure erase tool, which tells an SSD to clear every part of itself. Look for it on the maker's support site.

On a Mac with Apple silicon or a T2 chip, open System Settings > General > Transfer or Reset and choose Erase All Content and Settings.