How to Back Up to an External Drive

Backing up to an external drive keeps a separate copy of your files in case the computer is lost, damaged, infected by malware, or its internal storage fails. A backup can also help you move files to a replacement computer. Before starting, check that the drive has enough free space and that you know which files or folders you want to protect. The exact menu names below can differ slightly by operating-system version.

What You’ll Need

An external drive: This can be a USB hard drive, solid-state drive, or flash drive. For a full computer backup, choose one with more available capacity than the data you plan to save; some backup tools also need extra room for older versions.
A compatible connection: Check whether the drive uses USB-A, USB-C, or another connector. Use a suitable cable or adapter, and connect the drive directly if a hub causes problems.
Your computer and its power source: Keep a laptop plugged in during a large backup, and do not disconnect the drive while files are being copied.
Optional backup software: Windows and macOS include backup features, though available features vary by version. You can also copy selected files manually in File Explorer or Finder.

Step-by-Step

Decide what to protect. Choose between selected folders, such as Documents, Pictures, and Desktop, and a broader system backup that may include settings or other data. A simple file copy is easy to browse, while a system backup is usually restored through its backup application. Neither replaces keeping a separate copy of especially important files.
Check the drive and its contents. Connect it and open it in File Explorer on Windows or Finder on a Mac. Confirm that it appears and has enough free space. If it contains files, do not format or erase it unless you have confirmed that everything on it is backed up elsewhere; formatting deletes its contents.
Choose a backup method. For a few folders, select them and copy them to a clearly named folder on the external drive. On Windows, use File History or the backup options available in Settings or Control Panel; the route varies by version. On a Mac, use Time Machine from System Settings or System Preferences, depending on the version. Follow the prompts to choose the external drive and approve access if requested.
Set up automatic backups if useful. A scheduled or continuous backup can capture changes without relying on memory. In the backup tool, check which folders are included, how often it runs, and whether it keeps older versions. Leave the drive connected when the tool requires it, or reconnect it as directed by the software.
Start the backup and wait. For a manual copy, drag or copy the chosen files and folders to the destination. For a backup tool, select its option to start or run a backup if it does not begin automatically. Large amounts of data can take a while. Keep the computer awake and avoid editing or moving files that are actively being copied.
Verify the result. Wait for a completion message or confirm that the file transfer has finished. Open the external drive and check that expected folders and a few important files are present and readable. For a backup application, check its status or backup history too; a drive icon alone does not prove the backup completed.
Eject the drive safely. Use the operating system’s Eject or Safely Remove option, then disconnect it after the computer says it is safe. Keep the drive somewhere dry and secure, preferably separate from the computer. If it stays beside the computer, the same theft, fire, or electrical damage could affect both.

Common Mistakes

Assuming a connected drive is a backup. A drive must contain a complete, usable copy, and automatic backup software must run successfully. Check the backup status and contents.
Copying shortcuts instead of files. A shortcut or alias points to the original location; it does not contain the file. Copy the actual documents, photos, and folders.
Using a drive that is too small. A partial copy can leave out large folders or fail midway. Check the total amount of data and leave room for future additions and backup versions.
Formatting without checking. Formatting may be requested when a drive uses an unsupported file system, but it erases data. First copy any existing files somewhere safe, then decide whether reformatting is appropriate.
Unplugging during a transfer. This can interrupt the copy and may damage files or the drive’s file system. Wait for completion and eject properly.
Keeping only one copy. An external drive can fail, be lost, or be damaged. For especially important files, maintain another copy in a different location or use a separate backup method.

Tips

Use a descriptive folder name, such as “Computer backup,” and include a date if you make manual copies regularly.
Back up on a routine that suits how often your files change. A one-time copy becomes outdated as soon as you add or revise files.
Consider encryption when the drive may hold private or sensitive information. Set a password you can retain securely; losing it can make encrypted files inaccessible.
Keep the external drive disconnected when it is not in use if practical. This can reduce exposure to some malware and accidental deletion, though it does not protect against physical loss.
Test recovery occasionally by opening files or following the backup tool’s restore process for a sample item. A backup is useful only if you can retrieve its contents.
If moving between Windows and Mac, check drive formatting before relying on it. Some formats work better with one system than another, and reformatting erases the drive.

Troubleshooting

The drive does not appear: Check the cable, port, power switch, and connection. Try another port or cable, then restart the computer. On Windows, check Disk Management; on a Mac, check Disk Utility. Do not initialize, erase, or format a drive that may contain files you need.

The computer says the drive is full: Check its available space and the size of the selected folders. Remove only files you have another copy of, or use a larger drive. Backup software may need extra space to retain versions.

The backup stops or runs very slowly: Keep the computer powered and awake, reconnect the drive securely, and retry. If one file causes an error, note its name and check whether it is open, inaccessible, or too large for the drive’s file system. Avoid repeatedly unplugging a drive that is making unusual noises; stop using it and seek appropriate data-recovery help if its contents matter.

A file will not open from the backup: Try copying it to the computer first, then open the copy. Check that the transfer finished and that the correct version was saved. If using backup software, restore the file through that application rather than browsing its internal backup folders.

Frequently Asked Questions

Can I back up files by dragging them to the drive?

Yes. Manual copying works for selected files and folders, but it may not capture system settings or future changes automatically. Check the copied files and repeat the process when they change.

How often should I back up?

Back up often enough that you can tolerate losing any files changed since the last successful copy. Automatic backups are useful for files that change regularly; otherwise, make a fresh copy whenever you add important material.

Can I use the same external drive on Windows and Mac?

Sometimes, but compatibility depends on the drive’s file system and the computers’ versions. Check that both computers can read and write to the format before using it as the only backup, and do not reformat without first saving its contents.

Does copying files protect me if the drive is damaged?

No. A backup on one external drive can fail or be lost. Keep another copy of irreplaceable files in a separate place or through a separate backup method.

Is an external drive backup the same as cloud storage?

No. An external drive stores a local copy you control, while cloud storage keeps data on remote systems and requires an internet connection for many tasks. Each has different access, privacy, and recovery considerations.

Further reading: Apple Support and Microsoft Support. Details can change, so check the official page for anything that matters to you. Spotted a mistake? Tell us. How we write an answer.