What Reformatting Does and When You Need It

Reformatting erases everything on your hard drive and reinstalls your operating system from scratch. It is the nuclear option for a slow, virus-infected, or unstable computer — and it works because it removes every file, program, and setting you have added since the machine left the factory.

You should reformat when your PC has become so cluttered or compromised that normal fixes no longer work: when malware persists after antivirus scans, when the system crawls despite having free disk space, when programs crash constantly, or when you are selling or giving away the machine and want to erase your data permanently. Reformatting is also the fastest way to move from an old version of Windows to a new one.

The catch is that reformatting destroys everything. Your documents, photos, email, browser history, and installed programs all vanish. Before you start, you must back up anything you want to keep — and you must have a way to reinstall Windows or macOS afterward.

Key Takeaways

  • Reformatting erases your entire hard drive and reinstalls your operating system, so back up all your files to an external drive or cloud storage before you begin.
  • Windows users need a bootable USB drive with Windows installation media, which you can create on another computer using the Windows Media Creation Tool.
  • Mac users can reformat using Recovery Mode (Command + R at startup) without needing external media, though a Time Machine backup is still essential.
  • The process takes one to three hours depending on your drive size and internet speed, and your computer will restart multiple times during installation.
  • After reformatting, you will need to reinstall your programs and restore your files from backup — this second step takes as long as the reformat itself.

Back Up Your Files Before You Start

Reformatting destroys all your data. Before you touch anything, copy every file you want to keep to an external hard drive, USB stick, or cloud service. This includes documents, photos, videos, music, email archives, and browser bookmarks.

The fastest method is to plug in an external drive and drag your entire Documents, Pictures, and Downloads folders onto it. If you use OneDrive, Google Drive, or iCloud, make sure your important files have synced to the cloud first — you can check this by opening the sync app and waiting for the status to show "all files synced" or similar. For email, export your mailbox before you reformat; in Outlook, go to File > Open & Export > Import/Export, then choose "Export to a file".

If you have programs with settings or data you want to preserve — like browser bookmarks, game saves, or accounting software records — check whether those programs can export their data. Most modern software can. Once everything is copied, unplug the external drive and set it aside in a safe place.

Create a Windows Installation USB (Windows Only)

To reformat Windows, you need a bootable USB drive with Windows installation files on it. You create this on a different computer using the Windows Media Creation Tool, which is free from Microsoft.

On another working computer, go to microsoft.com/software-read/windows and read the Media Creation Tool. Plug in a blank USB drive (8 GB or larger), run the tool, and select "Create installation media for another PC". Choose your language and Windows version — if you do not know which version your PC runs, check Settings > System > About and look for "Edition". The tool will read the installation files and write them to the USB drive. This takes 10 to 30 minutes depending on your internet speed.

Once the tool finishes, eject the USB drive safely and label it clearly. Keep it plugged in or nearby — you will need it to start the reformat process.

Reformat a Windows PC

Shut down your PC completely. Plug in the Windows installation USB drive, then turn the computer back on and when ready press the key that opens the boot menu. This key varies by manufacturer: it is usually F12, F2, Esc, or Del, and it appears on the startup screen for one or two seconds. If you miss it, restart and try again.

From the boot menu, select the USB drive (it may be labeled "USB Device" or show the drive manufacturer's name). The Windows Setup screen will appear. Choose your language and keyboard layout, then click "Next". On the next screen, click "Repair your computer" in the lower left, then "Troubleshoot", then "Reset this PC".

You will see two options: "Keep my files" and "Remove everything". Choose "Remove everything" to reformat. Windows will ask whether you want to remove files only or fully clean the drive. For a used PC or one with malware, choose "Full clean" — it takes longer but is more thorough. For a personal machine you are keeping, "Remove files only" is faster and sufficient.

Windows will show you a list of drives. Select the drive you want to reformat (usually C:) and click "Next". The process will begin. Your computer will restart several times. Do not turn it off or unplug it. The entire process takes one to three hours depending on your drive size.

When it finishes, you will see the Windows setup screen asking for your region, language, and Microsoft account. Complete this setup, and your PC will restart into a fresh Windows installation.

Reformat a Mac

Shut down your Mac completely. Turn it back on and when ready hold Command + R until you see the Apple logo or a spinning globe. This boots into Recovery Mode, where you can reformat without needing external media.

When Recovery Mode finishes loading, you will see the macOS Utilities window. Click "Disk Utility", then click "Continue". In the left sidebar, select your main hard drive (usually called "Macintosh HD" or your computer name). Click the "Erase" button at the top.

A dialog will appear asking for a name, format, and scheme. For the name, type anything you like — this is just the label for your drive. For format, choose "APFS" if your Mac is from 2017 or later, or "Mac OS Extended (Journaled)" if it is older. For scheme, choose "GUID Partition Map". Click "Erase" and confirm. The process takes 10 to 30 minutes.

When the erase finishes, close Disk Utility and return to the Utilities window. Click "Reinstall macOS" and follow the prompts. Your Mac will read and install the operating system — this takes 30 minutes to two hours depending on your internet speed. Your computer will restart multiple times. When it finishes, you will see the macOS setup screen.

Reinstall Your Programs and Restore Your Files

After reformatting, your PC or Mac is blank. You now have two jobs: restore your backed-up files and reinstall your programs.

Plug in your external backup drive. On Windows, open File Explorer, navigate to your backup, and drag your Documents, Pictures, and other folders back to their original locations. On Mac, open Finder, go to your external drive, and drag folders back to your home directory. This can take 30 minutes to several hours depending on how much data you have.

For programs, you have two choices. If you kept the installer files for your software (in a folder on your backup drive), run them one by one. If not, read fresh copies from the publishers' websites. For Microsoft Office, Adobe Creative Suite, or other subscription software, sign in with your account and the software will set up automatically. For email, open your mail client, add your account, and import the mailbox file you exported before reformatting.

Browser bookmarks can usually be imported from your backup. In Chrome, go to Settings > Bookmarks > Bookmark Manager, click the three dots, and choose "Import bookmarks from HTML file". In Firefox, go to Bookmarks > Manage Bookmarks, click the gear icon, and choose "Import from HTML". In Safari, go to File > Import Bookmarks and select your exported file.

Troubleshooting Common Problems

If your computer will not boot from the USB drive, restart and try pressing a different boot key — F2, F12, Esc, and Del are the most common. If none of those work, restart and look carefully at the startup screen for text that says "Press [key] for boot menu" or similar. Some older PCs require you to enter the BIOS setup (usually by pressing F2 or Del during startup) and change the boot order manually.

If Windows Setup says "No drives were found", your hard drive may not be recognized. This usually means a driver is missing. On the Windows Setup screen, look for a "Load driver" option and insert a driver USB if you have one. If you do not, you may need to contact the PC manufacturer for help.

If your Mac gets stuck on the "Preparing to reinstall" screen, force restart by holding the power button for 10 seconds, then try Recovery Mode again. If it still fails, restart into Recovery Mode, open Disk Utility, and try erasing the drive a second time before reinstalling.

If your computer restarts into the old operating system instead of the new one after reformatting, the installation did not complete. Restart from the installation USB and try again. Do not turn off the computer during the process.

Frequently Asked Questions

Can I reformat my PC without losing my files?

Not with a full reformat — that erases everything by design. However, Windows offers a "Reset this PC" option that removes programs and settings while keeping your Documents and Pictures folders. This is faster than a full reformat but less thorough for malware removal. If you want to keep your files, use Reset instead; if you want a completely clean system, back up first and do a full reformat.

How do I know if my PC needs reformatting?

Reformat if your computer is extremely slow despite having free disk space, if antivirus scans find malware but the system still behaves strangely, or if programs crash constantly. For minor slowness, try uninstalling unused programs, clearing temporary files, or running Disk Cleanup first. Reformatting is the last resort, not the first fix.

What if I do not have another computer to create the Windows USB?

You can create a bootable USB on a Mac using the Windows Media Creation Tool if you have Parallels or another virtualization software installed. Alternatively, ask a friend or visit a library or internet café to create the USB for you. You only need 10 minutes on another computer.

Will reformatting remove viruses?

Yes — reformatting erases the entire drive, including any malware. However, if the virus is on your backup drive, you will restore it when you copy files back. Before restoring, scan your backup drive with antivirus software on a clean computer to make sure it is not infected.

How long does the whole process take?

Reformatting itself takes one to three hours. Restoring your files and reinstalling programs takes another one to four hours depending on how much data and software you have. Plan for a full day if you have a large amount of data or many programs to reinstall.