What is a swappable drive?

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To make the laptop smaller and lighter, many models have "swappable" or interchangeable drives. With a swappable drive, there is only space in the case for one drive. If you want to change from one type of disk drive to another, you just pull one out of the bay and put the other one in. In some laptops with swappable drives, you must turn the computer off first, change the drive and then reboot the computer. Other laptop models may have a "hot swappable" drive, in which you can interchange the drives without turning the computer off; this feature saves you the time involved in restarting the computer. While swappable drives allow you to use several types of drives in your laptop, remember that you will have to carry those extra drives with you if you want to use them on the go.

swappable drive usually relates to ur cd/dvd drives.
If you have a cd drive you can remove it via a switch release and slide in compatable cd writer or dvd/dvd writer.
basically its an added extra to make life simple.
just for those who dont have swappable drives dont mean you cant change update drives just means longer more technical precedure.