Selecting an external case may be the most difficult part of building your own external hard drive. There are hundreds of possibilities to choose from, ranging from basic, no-frills units to cases that could very well cost more than your Mac. This guide assumes you’re going to use an external case designed for a single 3.5” hard drive, the type most often used inside a Mac or PC. You can, of course, use a case for a 2.5” hard drive, the type used in laptop computers, if that’s the type of drive you have.
Selecting an External Case
- Select a case size. Standard internal hard drives use a 3.5" form factor; laptops generally use a 2.5" hard drive. The case you choose should be designed for the physical size of the hard drive you plan to use. By the way, a 3.5" drive is actually 4 x 5.75 x 1, and a 2.5" drive is 2.75 x 3.94 x 0.374.
- Pick the internal interface. The internal interface must match the type of interface your hard drive uses. There are two common types of interfaces, Serial ATA (SATA) and Parallel ATA (PATA). SATA is the newer of the two and is the type that Apple has been using since its G5 desktop computers. PATA is an older interface type that was also known as ATA (also often referred to as IDE).
- Pick the external interface. The external interface determines how the external case will connect to your Mac. Common choices are USB 2.0, FireWire 400, FireWire 800, and eSATA (External SATA). Many external cases provide more than one type of external interface. Almost all will have USB 2.0, with many also offering a FireWire connection. When all three types of external interfaces are offered, the case is often referred to as a universal case. All recent Macs have USB 2.0; most Macs also have FireWire.
