How to eject a memory card from your PC
You cannot just pull out a memory card that you have inserted in your PC. It may be tempting. But if you do pull out the memory card without properly ejecting it, the memory card can be damaged or the information stored on the card destroyed.
To eject your memory card:
Open the Computer window on your PC.
You can double-click the Computer icon on the desktop, or open the Start menu and choose Computer.
Click to select the memory card's icon.
You can find this icon in the part of the window labelled Devices with Removable Storage.
Click the Eject button on the toolbar or the drop down menu.
Pull the memory card from the card slot.
Be sure to store the memory card in a safe, static-free location when you are not using it.
Obviously, pulling out a drive while it is being written to could corrupt the data. However, even if the drive is not actively being written to, you could still corrupt the data. By default, most operating systems(OS) use what is called write caching to get better performance out of your computer. When you write a file to another drive; like a flash drive; the OS waits to actually perform those actions until it has a number of requests to fulfil, and then it fulfils them all at once (this is more common when writing small files). When you hit that eject button, it tells your OS to flush the cache; that is, make sure all pending actions have been performed; so you can safely unplug the drive without any data corruption.
Mac and Linux use write caching on pretty much all drives, and will let you eject any drive through your file manager. Windows, however, is a bit more mysterious on this front. It actually disables this write cache feature for drives it sees as "removable", because it knows people are likely to yank them out without ejecting (though you can still eject them by right-clicking on them and pressing "Eject"). As such, disabling this feature on removable drives decreases the chance of data corruption. It keeps the cache enabled on non-removable drives, though; and sometimes it recognizes external USB drives as not removable, which is why your USB drive does not have an eject button. Paradoxically, it's also why you need to eject that drive: since Windows does not see it as removable, it's enabled the write cache for it, increasing the chance of data corruption.
Windows has a few precautions in place for preventing data loss. However, the write cache is not the only thing that can cause data loss. Have you ever tried to eject a drive and gotten a "file is in use" error? Sometimes there is something going on in the background you do not know about or sometimes a program has still locked a file on the drive even if it is not using it. If you were to pull it out during one of these situations, you could still cause data loss. Ejecting it will warn you of the situation, and let you close the program in question
In the end, there is no reason not to eject your drives, and doing so will ensure your data is really safe. Windows users may be less likely to experience issues due to the way Windows handles removable drives, but they are not 100% safe. Ejecting the drive is a great habit to get into, since without it;
You would not always know if it were safe to remove or not.