Connecting an external hard drive to your Mac
Your Mac will recognize most external hard drives the moment you plug them in. Use the USB cable that came with the drive — one end goes into the drive itself, the other into any USB port on your Mac. If your drive uses USB-C and your Mac has only USB-A ports (or vice versa), you will need an adapter, which you can buy separately for under $15.
Wait about 10 seconds after plugging in. Your Mac will mount the drive automatically, meaning it prepares the drive for use and makes it visible. You should see the drive's name appear on your desktop, or if your desktop is hidden, it will show up in Finder on the left sidebar under "Locations".
If nothing appears after 30 seconds, the drive may need power. Some external drives draw power from the USB connection alone, but larger ones come with a separate power cable. Plug that cable into the drive and into a wall outlet, then wait another 10 seconds.
Key Takeaways
- External drives connect via USB cable and mount automatically on your Mac within seconds of plugging in.
- The drive will appear as an icon on your desktop or in the Finder sidebar under "Locations" once it is mounted.
- If the drive does not appear, check that the power cable is connected if the drive has one, and try a different USB port on your Mac.
- You can drag files to and from the external drive just as you would with any folder on your Mac.
- Always eject the drive before unplugging it to avoid losing data or corrupting files.
Opening the drive and viewing its contents
Once the drive appears on your desktop, double-click its icon to open it. A Finder window will open showing whatever files and folders are stored on that drive. From here, you can navigate through folders, open files, or drag new files onto the drive to copy them.
If you do not see the drive icon on your desktop, open Finder (the blue and white face icon in your dock) and look at the left sidebar. Under the "Locations" section, you should see your external drive listed by name. Click it once to select it, and its contents will appear in the main window on the right.
You can also add the drive to your Finder sidebar for faster access in the future. With the drive mounted, go to Finder menu at the top, click "Preferences", then the "Sidebar" tab. Check the box next to your drive's name, and it will stay in your sidebar even after you eject it.
Copying files to and from your external drive
Moving files to your external drive works the same way as moving files between folders on your Mac. Open a Finder window showing the files you want to copy. Then open another Finder window showing your external drive. Drag the files from the first window into the second, and they will copy over.
If you want to move files instead of copying them — meaning they will be removed from your Mac — hold down the Command key while dragging. The cursor will change to show a small arrow, indicating a move rather than a copy. Release the mouse, and the files will move to the drive and disappear from their original location.
You can also right-click a file or folder and select "Copy", then right-click inside the external drive window and select "Paste". This method works well if you are copying many items or if dragging feels awkward on your trackpad.
Checking how much space your drive has
To see how much storage space your external drive has and how much is in use, click the drive icon once to select it, then press Command and I together. A small window will open showing the total capacity, how much space is used, and how much is free.
If you need more detail — for example, which folders are taking up the most space — you can use a tool called Disk Utility. Open Finder, go to Applications, then Utilities, and double-click Disk Utility. Click your external drive in the left sidebar, then click the "Info" button at the top. This shows the same information in a slightly different layout.
If your drive is running low on space and you want to delete files to free it up, straightforward click the files or folders you want to remove and press Command and Delete, or right-click and select "Move to Trash". Empty your Trash afterward to permanently remove them.
Ejecting the drive safely before unplugging
Never unplug your external drive while your Mac is still using it. Always eject it first. The simplest way is to click the drive icon on your desktop and press Command and E, or right-click the drive and select "Eject".
You can also eject from Finder. Click the drive in the sidebar on the left, then look for the eject icon (an upward-pointing arrow) next to the drive's name. Click that icon, and the drive will eject. The icon will disappear from your desktop and sidebar.
Wait until the drive icon is completely gone before unplugging the cable. If you unplug while the Mac is still writing data, you risk losing files or damaging the drive's file system. Once the icon disappears, it is safe to unplug.
Troubleshooting a drive that will not mount
If you plug in your external drive and it does not appear, try these steps in order. First, try a different USB port on your Mac — sometimes a port stops working. Second, try a different USB cable if you have one available, since cables can fail. Third, restart your Mac and plug the drive in again after it boots up.
If the drive still does not appear, open Disk Utility (Applications > Utilities > Disk Utility). Look in the left sidebar for your external drive. If it is listed there but not mounted, click it and then click the "Mount" button at the top. If the drive appears in Disk Utility but shows a red exclamation mark or says "Not Mounted", the drive may have a file system problem that requires repair.
If Disk Utility shows a "Repair" button, click it and let it run. This can take several minutes. If no repair button appears, or if repair fails, the drive may have a hardware problem. At that point, contact the drive's manufacturer for support, or take it to a computer repair shop.
Understanding file formats and compatibility
Most external drives come formatted as either NTFS (common on Windows) or exFAT (works on both Mac and Windows). Your Mac can read both formats, but it can only write to exFAT and Mac-formatted drives. If your drive is NTFS and you want to copy files to it from your Mac, you will need to reformat it first.
To reformat a drive, open Disk Utility, click the drive in the left sidebar, and click "Erase" at the top. A dialog will appear asking what format you want. For a drive you plan to use with both Mac and Windows computers, choose "exFAT". For a drive you will use only with your Mac, choose "Mac OS Extended" or "APFS" — both are Mac formats and will give you slightly better performance.
Warning: erasing a drive deletes everything on it. Make sure you have copied any files you want to keep to your Mac or another drive before you erase.
Frequently Asked Questions
Why does my Mac say the drive is read-only?
A read-only drive means you can open and copy files from it, but you cannot add new files or delete existing ones. This usually happens if the drive is formatted as NTFS, which your Mac cannot write to. Reformat the drive as exFAT or Mac OS Extended in Disk Utility to fix this. If the drive is already exFAT or Mac-formatted, check whether the drive itself has a physical lock switch — some external drives have a small switch on the back that prevents writing.
Can I use the same external drive with both my Mac and a Windows computer?
Yes, if the drive is formatted as exFAT. Both Mac and Windows can read and write to exFAT drives. If your drive is currently formatted as NTFS or Mac OS Extended, reformat it as exFAT in Disk Utility. Keep in mind that reformatting erases everything on the drive, so back up any files first.
What happens if I unplug the drive without ejecting it?
Unplugging without ejecting can corrupt files or damage the drive's file system, especially if your Mac was in the middle of copying or saving data. If you accidentally unplug, plug it back in and run Disk Utility to check for errors. In most cases the drive will be fine, but it is always safer to eject first.
How do I know if my external drive is failing?
Signs of a failing drive include the drive not mounting, making clicking or beeping sounds, taking a very long time to copy files, or Disk Utility showing errors that cannot be repaired. If you notice any of these, stop using the drive when ready and back up any files you can still access. Contact the manufacturer or a repair shop for help recovering data.
Do I need to eject the drive before putting my Mac to sleep?
No. Putting your Mac to sleep does not affect the external drive. You only need to eject the drive if you plan to unplug it or move it to another computer. If you are just closing your Mac's lid or letting it sleep, you can leave the drive plugged in and mounted.