PC & laptop with no extra HDD/SSD slot: If there is no location for the second disk inside your device, you are supposed to use a USB-to-SATA cable or adapter to connect it to your computer.

This removable hard disk can be popped in and out of the PC, without opening the case or using tools, even when the machine is running. The PCs with this feature still have the standard built-in ...

TEAC America has introduced its new PDrive, a multifunction drive, a portable hard disk drive that connects to a Mac or PC using USB 2.0 and also features its own built-in flash memory card slots.

A Japanese company called Marshal (yes, one "l") announced the MAL 1925 today, a netbook stand that doubles as a DVD super multi drive, has room for a second HDD and comes with an extra USB 2.0 port.