The building blocks of digital images are bits. These can either be zero or one. Magnetic storage devices such as hard disks distinguish a one from a zero by changing the magnetic properties of the disk in that location. The great thing about hard disks is that their capacities are constantly increasing while prices are constantly dropping. One terabyte hard disks currently retail arrount US$100.  Such hard disks can hold about 350,000 six megapixel JPEG or 100,000 six megapixel uncompressed RAW images. That’s about 3500 JPEG or 1000 RAW images per dollar.

Magnetic Storage Device

If you store images on your computer, it is recommended to store them on a dedicated partition (or if you have multiple hard disks, then ideally on a different physical drive) than your operating system (e.g. use C:\ for the operating system and software, and D:\ or E:\ for your images).  This ensures that if your operating system crashes and you need to reinstall it, your images will be preserved.

Portable housings exist with built-in international 100-240V power supply, USB 2.0 (Hi-speed), and FireWire IEEE1394 connections, with very cheap prices.  To avoid overheating, get a case with a large diameter cooling fan below the hard disk.