The Basic Steps to Copy Your Files

Backing up your computer to an external hard drive means copying your files, folders, and system data to a separate device so you have them if your computer fails, gets stolen, or is damaged. The simplest method is to plug in the external drive, open your file manager, and drag folders into it — but that only copies what you select, not your entire system setup or hidden files.

Most computers come with built-in backup software that does a complete job automatically. Windows has File History (Windows 10 and 11) or Backup and Restore (older versions). macOS has Time Machine. Both run on a schedule you set and back up everything — your operating system, programs, settings, and data — so you can restore your computer to exactly how it was on any backup date.

The choice between manual copying and automatic backup software depends on what you need to protect. Manual copying works if you only care about documents, photos, and videos. Automatic backup is better if you want to restore your entire computer after a crash, because it captures system files and program settings that manual copying misses.

Key Takeaways

  • Windows File History and macOS Time Machine back up your entire computer automatically, while manual copying only backs up the folders you select.
  • Your external drive must be formatted to match your computer's system — NTFS for Windows, APFS or Mac OS Extended for macOS — or the backup software will not work.
  • Automatic backups run on a schedule (usually daily or weekly) and keep multiple versions of your files, so you can recover an older version if needed.
  • A full system backup takes longer the first time but runs faster on later backups because the software only copies what changed.
  • Keep your external drive unplugged when you are not backing up, because ransomware or malware on your computer can infect connected drives.

Setting Up Windows File History

File History is built into Windows 10 and 11 and backs up your Documents, Desktop, Downloads, Pictures, Music, and Videos folders, plus any files stored in OneDrive. It does not back up your operating system or installed programs — only your personal files and their history.

Plug in your external drive, then open Settings (Windows key + I), go to System > Backup, and click "Backup with File History." Windows will ask you to select the external drive as your backup location. Once you confirm, File History runs automatically every hour by default. You can change the frequency by going back to Settings > System > Backup and clicking "More options," then "How often do you want to back up your files?"

File History keeps multiple versions of each file — if you accidentally delete something or overwrite it, you can right-click the folder in File Explorer, select "Restore previous versions," and choose which version you want back. This works for any folder in your Documents, Desktop, Downloads, Pictures, Music, or Videos — not for files elsewhere on your drive.

Setting Up macOS Time Machine

Time Machine backs up your entire Mac — system files, programs, settings, and data — so you can restore your computer to any point in time. It is the closest thing to a complete system backup on macOS.

Plug in your external drive. If it is new or has never been used with a Mac, the system will ask if you want to use it for Time Machine backups. Click "Use as Backup Disk." If you do not see this prompt, open System Settings, go to General > Time Machine, click "Add Backup Disk," and select your external drive.

Time Machine runs automatically every hour once you set it up. You can change the backup frequency by opening System Settings > General > Time Machine and looking for the interval option (this varies by macOS version). To restore files, click the Time Machine icon in the menu bar, browse to the date you want, select the files you need, and click "Restore." To restore your entire system after a crash, restart your Mac while holding Command + R to enter Recovery Mode, then choose "Restore from Time Machine Backup."

Formatting Your External Drive for Your Operating System

Your external drive must be formatted in a file system your computer recognizes. Windows uses NTFS, and macOS uses APFS (newer Macs) or Mac OS Extended (older Macs). If you format the drive on one system, it may not work with the other.

To format on Windows, plug in the drive, open File Explorer, right-click the drive, select "Format," choose NTFS from the "File system" dropdown, give it a name, and click "Start." This erases everything on the drive, so copy off any files you need first.

To format on macOS, plug in the drive, open Disk Utility (Applications > Utilities), select the drive in the left sidebar, click "Erase," choose APFS or Mac OS Extended from the "Format" dropdown, name it, and click "Erase." Again, this erases the drive completely.

If you need to use the same external drive with both Windows and macOS computers, format it as exFAT instead. Both systems can read and write to exFAT, though neither backup software (File History or Time Machine) works with exFAT — you would have to copy files manually instead.

What Happens During Your First Backup

The first backup takes much longer than later ones because your computer is copying everything — on a typical computer with 500 GB of data, expect 2 to 8 hours depending on the speed of your external drive and USB connection. Do not unplug the drive or shut down your computer during this time, or the backup will fail and you may have to start over.

After the first backup finishes, later backups run much faster because the software only copies files that changed since the last backup. A daily backup after the first one usually takes 15 minutes to an hour.

If your computer goes to sleep during a backup, the backup pauses and resumes when you wake it. You can check the progress by looking at the backup software's status — in Windows, go to Settings > System > Backup and look for "Last backup" to see when the most recent backup completed. On macOS, click the Time Machine icon in the menu bar to see the backup progress.

Keeping Your Backup Safe from Malware

Ransomware and other malware can spread to any drive connected to your computer, including your external backup drive. If malware encrypts your files, it can also encrypt your backups if the drive is plugged in when the infection happens.

The safest practice is to unplug your external drive when you are not actively backing up. Windows File History and macOS Time Machine can be set to run on a schedule — for example, every night at 2 a.m. — so you can plug in the drive before bed, let it back up, and unplug it when you wake up. This way, if your computer gets infected during the day, your backup from the night before is still safe.

Some people keep two external drives and rotate them — one stays at home, one stays at a different location or in a safe. This protects against both malware and physical loss (fire, theft, or damage). If you use this method, plug in each drive only when you are ready to back up, then unplug it when ready after.

Restoring Files or Your Entire System

If you lose a single file, you do not need to restore your entire backup. In Windows File History, right-click the folder containing the file, select "Restore previous versions," choose the date you want, and click "Restore." In macOS Time Machine, click the Time Machine icon in the menu bar, navigate to the date you want, select the files, and click "Restore."

If your computer crashes or fails to start, you can restore your entire system from the backup. On Windows, restart your computer and press F11 or F12 (the key varies by manufacturer) to enter recovery mode, then look for an option to restore from backup. On macOS, restart while holding Command + R, select "Restore from Time Machine Backup," and follow the prompts. This process can take 1 to 4 hours depending on how much data you are restoring.

Before you restore, make sure your external drive is plugged in and recognized by your computer. If your computer will not start at all, you may need to use a different computer to access the backup drive and copy files manually, or take your computer to a repair shop.

Frequently Asked Questions

How much space do I need on my external drive?

Your external drive should be at least as large as the data on your computer, plus 20 to 30 percent extra. If your computer has 500 GB of files, use a 750 GB or 1 TB external drive. Backup software keeps multiple versions of files, so it uses more space than a single copy would.

Can I back up to a cloud service instead of an external drive?

Yes — services like OneDrive, Google Drive, and iCloud back up your files to the internet. Cloud backup is convenient because you do not have to plug in a drive, but it is slower, costs money per month, and requires an internet connection. An external drive is faster and has no monthly cost, but you have to remember to plug it in.

What if my external drive is not showing up on my computer?

Try plugging it into a different USB port — some ports are faster or more reliable than others. If it still does not show up, the drive may not be formatted correctly for your system, or the drive itself may be failing. Try plugging it into a different computer to see if it appears there. If it does not appear on any computer, the drive may need repair or replacement.

Do I need to eject my external drive before unplugging it?

Yes. On Windows, right-click the drive in File Explorer and select "Eject." On macOS, click the eject icon next to the drive name in Finder. This tells your computer to finish writing any data and close the connection safely. If you unplug without ejecting, you risk corrupting files on the drive.

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

Yes, but you need to be careful about formatting. If both computers use the same operating system (both Windows or both macOS), you can partition the drive into two sections, one for each computer. If one is Windows and one is macOS, format the drive as exFAT so both can access it, but you will have to copy files manually instead of using automatic backup software.