What's really going to happen if I unplug that flash drive? by Kim Komand

I regularly get questions from listeners about unplugging USB drives.

There's a lot of confusion about the best way to disconnect a drive from your computer.
I'm not talking about how to actually physically unplug it - I know you've got that down. I'm talking the steps to take before you yank it out.

Windows users have the Safely Remove Hardware feature in the lower-right notification area of the desktop. It looks like a USB plug with a green check mark. You're supposed to click it and select the drive you want to eject. After a few seconds, you will get a message saying you can unplug it safely.

For Mac users, you have to click the Eject icon next to the drive in the Finder or drag the drive icon down to the Eject icon on the Dock (it shows up where the Trash usually sits). Once the drive icon disappears, you can unplug.

But do you really need to do this every time? Plenty of people just yank out the drive and nothing bad happens to them, right? Let's take a look at why these features exist in the first place.

Both Windows and Mac use something called "caching" when dealing with removable drives. Information you send to the drive isn't always put on the drive right away, but sticks around in your computer's memory for a while first.

That's because writing and reading from a removable drive is slow and your computer's memory is fast. Caching lets you work at full speed. Here's an example.

Imagine you open a Word document from a USB drive. As you're typing, you save it regularly - as you should.

Instead of taking a full second to write to the drive every time you save, it temporarily saves it to your computer in a few milliseconds. When you're done with the file, the computer moves the final version over to the drive.

This means you aren't sitting around waiting every time you hit the Save button - click here to learn a much faster way to save. For editing larger files like photos and videos, caching makes even more sense.

When you use Windows' "Safely Remove Hardware" feature or Eject on a Mac, you're telling the system that you're done with the files and the drive. That's its cue to move everything to the drive that it hasn't moved yet. The computer also checks to make sure no programs are still using the files.

But what happens if you unplug the drive before the files are moved, or while the file is still open in a program? Unfortunately, I've seen the answer firsthand.

I once had to try and recover a final paper for a college student who unplugged her USB drive without ejecting on a Mac. Short story: It didn't end well.

There is an exception, of course. For the latest versions of Windows, Microsoft disabled caching on USB flash drives because too many people were just pulling them out anyway. So in Windows, as long as you wait for the activity light on a flash drive to stop flashing for a few seconds - and the file isn't open - you're OK to pull it out.

However, this doesn't work for external hard drives or memory cards, and it certainly doesn't work on Macs. That's why it's a good idea to be in the habit of ejecting all your drives on Windows and Mac before unplugging. It helps to make sure nothing goes wrong.

Now, sometimes in Windows you'll try to eject a drive and it will say that it can't. That usually means a file from the drive is still open in a program. Until the program is closed, you're stuck.

You can try hunting through your open programs for the culprit, or you can grab a program like Unlocker. It will tell you what program is keeping you from ejecting the drive so you can go close it.

In the worst case, you might have to restart your computer to fix this problem. It's inconvenient, but if you had just yanked out the USB cord, you might have lost the file entirely. That makes it worth the little extra effort.