Computers, Laptops & Tablets Apple Build Your Own External Hard Drive External drives expand your storage space without opening the computer case by Tom Nelson Writer Tom Nelson is an engineer, programmer, network manager, and computer network and systems designer who has written for Other World Computing,and others. our editorial process Facebook Twitter Tom Nelson Updated on September 17, 2020 Apple Macs iPad Tweet Share Email External hard drives are a great way to expand your Mac’s storage capacity. They’re a particularly good choice if you have a Mac that doesn’t allow you to easily add an internal hard drive or swap out the existing hard drive for a larger one. You can purchase ready-made external hard drives; just plug them in and go. But you pay for this convenience in two ways: in actual cost and in limited configuration choices. TimeStopper / Getty Images Building your own external hard drive eliminates the drawbacks of a ready-made unit. It can be significantly less expensive, especially if you repurpose a hard drive you already own. For example, you may be able to steal one from an older computer you no longer use, or you may have a leftover hard drive that was replaced with a larger model. There’s no sense in letting these unused hard drives go to waste. If you build your own external hard drive, you get to make all the decisions about configuration. You can choose the size of the hard drive, as well as the type of interface you want to use (USB, FireWire, eSATA, or Thunderbolt). You can even choose an external case that lets you use all of these popular methods of connecting an external enclosure to a computer. Here's what you'll need: A hard drive. This can be a drive you purchased just for this project, or an unused hard drive from another computer.An external case. External cases are available from many retail and online sources. They include a power supply, an interface adapter, and a method of mounting a standard form factor hard drive (either 3.5” or 2.5”).A screwdriver. Usually, a small Phillips #1 or #2 will do, although the size you need is dependent on the design of the external case.About 10 minutes of free time. Yes, we really mean 10 minutes. This is a simple project. If you can wield a screwdriver, you can build an external hard drive. Choosing a Case 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-inch hard drive, the type most often used inside a Mac or PC. You can, of course, use a case for a 2.5-inch 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-inch form factor; laptops generally use a 2.5-inch hard drive, and SSD (Solid State Drives) commonly use the 2.5-inch format. The case you choose should be designed for the physical size of the hard drive you plan to use. A 3.5-inch drive is actually 4 inches by 5.75 inches by 1 inch, and a 2.5-inch drive is 2.75 inches by 3.94 inches by 0.374 inches.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 and Parallel ATA. 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, USB 3.0, FireWire 400, FireWire 800, eSATA (External SATA), and Thunderbolt. Many external cases provide more than one type of external interface. Almost all have USB 3.0, with many also offering eSATA or Firewire connections. When all multiple types of external interfaces are offered, the case is often referred to as a universal case. All recent Macs have USB 3.0 and Thunderbolt. Choosing a Hard Drive Choosing the hard drive is one of the main benefits of building your own external hard drive. It allows you to repurpose a hard drive that would otherwise just gather dust, reducing the total cost of adding storage to your Mac. You can also opt to purchase a new hard drive that meets your specific needs. Selecting a Hard Drive Use an existing drive. You can reuse a drive from an older computer, or a drive you replaced with a larger model. Repurposing a drive is a good way to both reduce your expenses and recycle your electronics.Note the drive interface. Your existing hard drive’s interface must match the internal drive interface used by the enclosure you selected.Check the drive capacity. Drive size is usually listed on the drive’s label, but manufacturers usually code it into the drive model number, making it hard to decipher. If you can’t figure it out, look up the size of the hard drive on the manufacturer’s web site. The size is important only to help determine whether it makes sense to use an existing drive in a new enclosure. Small hard drives (60 GB or less) may not be a good choice, both because of their relatively limited storage capacity and their probable age.Purchase a new drive. Buying a new drive increases the cost of your external hard drive project, but it also gives you maximum flexibility, so you end up with exactly what you need in terms of size and performance.SATA III drives are the logical choice when purchasing a drive. They are the newest and fastest, and because all drive manufacturers make drives in this format, they offer the widest selection.Make sure the drive and the enclosure’s internal interface are compatible. If you buy a new SATA III drive, the enclosure must have at minimum a SATA, SATA II, or SATA III internal interface. Opening the Case Each manufacturer has its own way of opening an external case to add a hard drive. Read the instructions that came with your enclosure. The instructions here are for a generic case that uses a common assembly method. Disassemble the Case In a clean and well-lit location, prepare for disassembly by gathering the tools you need. A Phillips screwdriver is usually all that is required. Keep one or two small jars or cups nearby to hold small screws or parts removed during the disassembly process.Remove the two retaining screws. Most enclosures have two or four small screws located on the back, usually one or two on each side of the panel that holds the power and external interface connectors. Put the screws in a safe place for later.Remove the back panel. After you remove the screws, remove the panel that houses the power and external interface connections. This process usually only requires a little pull with your fingers, but if the panel seems stuck, a small straight-blade screwdriver slipped between the panel and the top or bottom cover plates may help. Don’t force the panel, though; it should just slip off. Check the manufacturer’s instructions if you’re having trouble.Slide the internal carrier out of the housing. After you remove the panel, slide the internal carrier out of the case. The carrier contains internal interface electronics, the power supply, and the mounting points for the hard drive. Some enclosures have wiring that connects the carrier to a switch or display light mounted in the front of the enclosure. With those enclosures, you don’t remove the carrier from the case, but only slide it out far enough to allow you to mount the hard drive. Attach the Hard Drive There are two methods of mounting a hard drive to a case. Both methods are equally effective; it’s up to the manufacturer to decide which to use. Hard drives may be mounted by four screws attached to the bottom of the drive or by four screws attached to the side of the drive. One method that is becoming popular is to combine the side mounting points with a special screw that has a rubber-like sleeve. When attached to the drive, the screw acts as a shock absorber to help prevent the hard drive from damage arising from the bounces and bumps an external enclosure can produce when you move or carry it around. Mount the Drive in the Case Install the four mounting screws per the manufacturer’s instructions. It’s usually easiest to install one screw and leave it loose, then install another screw diagonally across from the first one. This pattern helps ensure that the mounting holes in the case and the hard drive align correctly. After you insert all of the screws, tighten them down by hand; don’t exert excessive force.Make the electrical connections between the case and the hard drive. There are two connections to be made, the power and the data. Each runs in its own cable assembly. You may find that making the connections is a bit difficult because of cramped space. Sometimes it’s easier to reverse the order for mounting the hard drive. Install the electrical connections first and then mount the drive to the case with the mounting screws. This sequence gives you more working room to get those stubborn cables connected. Reassemble the Case You’ve mounted the hard drive to the case and made the electrical connection. Now it’s time to button the case back up, which is a matter of reversing the disassembly process you performed earlier. Put It Back Together Slide the hard drive carrier back into the case. Check the internal electrical wiring to make sure that no cables are pinched or in the way as you slide the case and carrier back together.Snap the rear panel into place. Make sure the edges of the panel and the case line up and are a good fit. If they fail to line up, chances are a cable or wire in the case has been pinched and is preventing the case from closing completely.Screw the rear panel into place. Use those two small screws you set aside earlier to finish closing the case. Connect Your External Enclosure to Your Mac Your new enclosure is ready to go. All that’s left to do is to make the connection to your Mac. Making Connections Attach power to the enclosure. Most enclosures offer a power switch. Make sure the switch is set to off. Then, plug the included power cord or power adapter into the enclosure.Connect the data cable to your Mac. Using the external interface of your choice, connect the appropriate data cable (FireWire, USB, eSATA, or Thunderbolt) to the enclosure and then to your Mac.Switch the enclosure’s power on. If the enclosure has a power-on light, it should be lit. After a few seconds, your Mac should recognize that an external hard drive has been connected. That’s it You’re ready to use the external hard drive you built with your Mac and enjoy all that extra storage space. Using the Drive A few words of advice about using external enclosures. Before unplugging the enclosure from your Mac or turning off the enclosure’s power, first unmount the drive. Either select the drive from the desktop and drag it to the Trash, or click the little eject icon next to the drive’s name in a Finder window. When the external drive is no longer visible on the desktop or in a Finder window, you can safely turn its power off. If you prefer, you can also just shut down your Mac. The shutdown process automatically unmounts all drives. After your Mac has shut down, you can turn off the external drive.