external harddrive name?help?

i know this sounds nooby so i apoligise in advance.
im looking for something that allows me to have my harddrive on the outside so i can switch it as and when i need to, iv been told theres a device that plugs in though usb and has its own power supply and a ide cable attatched and u can just plug ur hdd into it.
Whats the name of the device im after.
Any help is appreciated
cheers