How to Back Up Your Computer to an External Hard Drive

What You Need Before You Start

To back up your computer to an external hard drive, you need three things: an external hard drive with enough storage space for your files, a USB cable (usually included with the drive), and about 30 minutes to an hour depending on how much data you have. Most external drives come formatted and ready to use straight out of the box, though you may need to format it yourself if it's older or was used on a different computer.

Check how much storage space your files take up before you buy a drive. On Windows, right-click your C: drive, select Properties, and look at the "Used space" number. On Mac, click the Apple menu, select About This Mac, then Storage. Buy a drive with at least 50% more capacity than your current files use—if your files take up 500 GB, get a 1 TB (1,000 GB) drive. This gives you room to back up again later as your files grow.

Key Takeaways

Connect the external drive with its USB cable, wait for your computer to recognize it, then open File Explorer (Windows) or Finder (Mac) to confirm it appears.
On Windows, use File History or System Image to back up automatically; on Mac, use Time Machine from System Preferences to set up scheduled backups.
Your first backup will take several hours if you have a lot of files, but after that, only new and changed files are backed up, which is much faster.
Keep the external drive in a safe, dry place away from heat and direct sunlight, and unplug it when you are not backing up to extend its lifespan.

Connecting Your External Drive and Checking It Works

Plug the external hard drive into a USB port on your computer using the cable that came with it. Wait 10 to 15 seconds for your computer to recognize the drive. On Windows, you should see a notification pop up in the bottom right corner saying the drive is ready to use. On Mac, the drive name will appear on the desktop and in the Finder sidebar on the left.

Open File Explorer on Windows (press Windows key + E) or Finder on Mac (click the Finder icon in the dock) and look for your external drive in the list. Click on it once to open it. If the drive opens and shows an empty folder, it is working correctly. If you see an error message or the drive does not appear, try unplugging the cable, waiting 10 seconds, and plugging it back in. If it still does not work, the drive may need to be formatted—see the Frequently Asked Questions section below.

Setting Up Automatic Backups on Windows

Windows has a built-in backup tool called File History that automatically backs up your Documents, Pictures, Music, Videos, and Desktop folders. Open Settings (press Windows key + I), click System on the left, then scroll down and click About. Click Advanced system settings, then click System Protection. Click Configure, select "Restore system settings and previous versions of files," and click OK.

Now go back to Settings, click System, then click Backup on the left side. Under "Back up using File History," click Add a drive and select your external hard drive from the list. Windows will ask how often you want to back up—the default is every hour, which works well for most people. Click More options, scroll down to "Back up these folders," and confirm that Documents, Pictures, Desktop, and Downloads are checked. You can add other folders if you want. Windows will now back up automatically whenever your external drive is plugged in.

Setting Up Automatic Backups on Mac

Time Machine is Mac's built-in backup tool and is the easiest way to back up your entire computer. Plug in your external drive, then click the Apple menu in the top left corner and select System Settings. Click General on the left, then scroll down and click Time Machine. Click Add Backup Disk and select your external hard drive from the list.

Mac will ask if you want to encrypt the backup—this adds a password to protect your files, which is a good idea if your drive might be lost or stolen. Click Encrypt Disk if you want this, or Skip if you do not. Time Machine will start backing up when ready and will continue automatically every hour as long as the drive is plugged in. Your first backup may take several hours, but you can use your computer normally while it runs in the background.

What Happens During Your First Backup

The first time you back up, your computer will copy every file on your hard drive to the external drive. This includes your operating system, programs, documents, photos, videos, and settings. Depending on how much data you have, this can take anywhere from 30 minutes to 8 hours or more. Do not unplug the drive or shut down your computer during this time, or the backup will fail and you will have to start over.

You can use your computer while the backup runs, but it will be slower than usual because the backup is using some of your computer's processing power. If you need your computer to run at full speed, wait until evening or a time when you are not using it. After the first backup finishes, future backups will only copy new files and changes you made, so they will be much faster—usually 5 to 30 minutes depending on how much you have changed.

Checking That Your Backup Worked

On Windows, open File Explorer, click your external drive, and look for a folder called "FileHistory." Inside, you should see folders for each user account on your computer, and inside those, folders for Documents, Pictures, Desktop, and other locations. Click into one of these folders and you should see copies of your files with dates next to them. If you see your files there, the backup worked.

On Mac, click the Time Machine icon in the menu bar (top right corner of your screen) and select "Enter Time Machine." You will see your files arranged by date, with the most recent backup at the far right. Click on a date and you should see your files as they were on that day. If you can see your files and dates, Time Machine is working correctly. Exit Time Machine by pressing Escape or clicking the X button.

Caring for Your External Drive and Backing Up Again

External hard drives are durable but not indestructible. Keep your drive in a cool, dry place away from direct sunlight, heat sources, and magnetic fields. Do not drop it or bump it while it is plugged in and running. Unplug the drive when you are not backing up—leaving it plugged in all the time wears out the drive faster. Most external drives last 3 to 5 years with normal use.

Your backup is only useful if it stays current. Plug in your external drive at least once a week so Windows File History or Mac Time Machine can back up any new files or changes. If you go months without backing up, your backup will not include recent work. If your computer fails or gets damaged, you will only be able to recover files from the last time you backed up. Set a calendar reminder to plug in your drive weekly, or leave it plugged in permanently if you have space on your desk.

Frequently Asked Questions

How do I restore files from my backup if my computer breaks?

On Windows, plug the external drive into a working computer, open File Explorer, navigate to the FileHistory folder on the drive, find the file you need, right-click it, and select Restore. On Mac, plug the drive in, click Time Machine in the menu bar, select "Enter Time Machine," find the date when the file existed, click on it, and click Restore. You can restore individual files or your entire computer.

Do I need to format my external drive before using it?

Most new external drives come pre-formatted and ready to use. If your drive does not appear in File Explorer or Finder, or if you see an error message, you may need to format it. On Windows, right-click the drive in File Explorer and select Format. On Mac, open Disk Utility (search for it in Spotlight), select the drive, click Erase, name it, and click Erase again. Warning: formatting erases everything on the drive, so only do this if the drive is empty or you do not need what is on it.

Can I use the same external drive to back up multiple computers?

Yes, but each computer needs its own backup folder on the drive. On Windows, File History automatically creates separate folders for each computer. On Mac, Time Machine will ask you to choose a new backup disk or use the existing one—select the existing one and it will create a separate backup for the new Mac. Make sure the drive has enough space for all the backups combined.

What if my external drive is running out of space?

Buy a larger external drive and set up your backup software to use the new drive instead. You can keep the old drive as an archive of older backups, or erase it and use it for something else. On Windows, go to Backup settings and click "Add a drive" to switch to the new drive. On Mac, click Time Machine settings and select the new drive.

Is an external hard drive backup safe from viruses?

An external drive backup protects your files from hardware failure, but not from viruses that are already on your computer. If your computer gets infected, the virus may also back up to the external drive. Keep your antivirus software up to date and run regular scans. If you suspect your computer is infected, scan it before backing up, or unplug the external drive and have the computer checked by a professional.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.