How to get Time Machine to back up booted or partitioned disks

Apple's built-in Time Machine app makes it simple to back up Mac data. Here, you'll learn how to choose a backup disk and set encryption, when necessary.

• Our favorite: G-Technology G-Drive 1TB ($72)
• Compact: SanDisk Extreme Portable External 250B, 500GB, 1TB, 2GB (starting at $65)
• Sleek choice: LaCie Porsche Design 1TB, 2TB, 4TB (starting at $75)

How it's done

Follow these instructions to select drives to backup:

1. In System Preferences, choose Time Machine.
2. Next, click Select Backup Disk, Select Disk, or Add or Remove Backup Disk. Your choice will depend on whether you've already had a backup disk set up on your Mac.

3. Highlight the disk you'd like to use for backing up, then choose Use Disk.
4. If applicable, check Encrypt Backups. For an explanation, see below.

5. If you wish to use multiple backup disks, repeats the steps above.
6. After selecting encryption, you'll be asked to type in a password.

As explained by Apple: "Time Machine works best if you use your backup disk only for Time Machine backups. If you keep files on your backup disk, Time Machine won't back up those files, and the space available for Time Machine backups is reduced."

As we previously explained, if you forget your encryption password, no one can help you recover your data -- including Apple.

A good rule of thumb: if it's more important that no one ever gets access to your data, even to your detriment, encryption is good. If, however, your data's safety is more important (like your family photos, movies, etc.) then never encrypt.

By default, Time Machine will back up everything on your Mac. To exclude items:

1. In System Preferences, choose Time Machine.
2. Click the Options... button in the lower right corner of the Time Machine system preference panel.
3. Click the + button to begin the process of excluding files.

4. Highlight the file(s) you'd like to exclude, then click Exclude.
5. Repeat Step 5 if there are other files or folders from your computer you want to exclude from Time Machine backup.
6. When you're finished selecting files, click on Save.

Time Machine will tell you exactly how much you're excluding and will attempt to estimate the size of a full backup with those exclusions in place.

Our top equipment pick

There are countless hard drives available that support Apple's Time Machine app for backup purposes. These three are among the best on the market.

Also available with 2TB and 4TB, G-Technology's G-Drive is one of the easiest drives to use for backup. Just plug it in, and you're halfway there! It's available in silver, space gray, and rose gold.

The following hard drives are also among our favorites for 2019.

SanDisk Extreme Portable External 250B, 500GB, 1TB, 2GB (starting at $65 at Amazon)

This product proves that even hard drives can be beautiful.

LaCie Porsche Design 1TB, 2TB, 4TB (starting at $75 at Amazon)

LaCie is well known for its backup devices; this is one of the most popular on the market.