Removable Hard Disk Trays

An interesting compromise between internal and external hard disks is the removable hard disk drive tray. A tray is installed into a standard PC case drive bay that allows regular internal hard disks to be placed into it. You then can swap the internal hard disk with another one without opening up the case, allowing you to use hard disks as a removable storage medium. In a way, the concept is similar to the way a removable car stereo is designed. These trays are also commonly called mobile racks, drive caddies and several other names.

Shown above is the Kingwin KF-21-IPF mobile rack system that I use on my
work desktop PC for backups and file archiving. The drive fits into the
removable tray (bottom) which fits into the stationary docking station (top). The
stationary portion is installed into a standard 5.25" drive bay and connected to
a regular IDE/ATA cable. On the right-hand side you can see the lock that
secures the tray in place, as well as indicator lights for power and drive activity.

For certain applications, this are the ideal removable storage device: it uses regular hard disks, which are very fast, highly reliable, very high capacity and very inexpensive in terms of dollars per byte of storage. They can be used for backup purposes (secondary to a regularly-installed standard internal hard disk)--see here for more information on this idea. Removable trays can also be used to allow the use of different operating systems on the same PC (though there are simpler ways to do this) and to allow different people to use the same PC while keeping their data and programs totally separate.

If you decide to use a mobile rack system, be sure to check out the specifications of the unit you are considering carefully. Different models come with support for different speed drives, some are made primarily of metal and others of plastic, and so on. Metal units will provide better cooling than plastic ones. Some also come with an integrated cooling fan, which is a good idea especially for higher-RPM drives.

Warning: If you decide to set up this sort of arrangement with your PC, remember that regular internal hard drives are designed under the assumption that they will be installed inside the PC and left there. Be sure to handle them properly, and especially, to observe ESD precautions.