How to Upgrade Your Mac's Hard Drive

Upgrade your hard drive to something bigger, faster, or both

Upgrading a hard drive is one of the most popular Mac DIY projects. A Mac buyer will usually purchase a computer with the minimum configuration Apple offers and then add external storage or replace the internal hardware with a larger one when needed.

Not all Macs have user-replaceable hard drives. But you can even replace a closed Mac's drive under some circumstances. Usually, this means taking it to an authorized service provider.

You can also try replacing the drive yourself, but you'll want to familiarize yourself with the process first. Opening your computer may also void the warranty.

A computer’s hard drive.

When to Upgrade a Hard Drive

The main reason you'd want to upgrade your hard drive is simple: Swap it out for a larger one if you run out of space.

But you may find other opportunities to upgrade. To keep a drive from filling up, some users keep deleting less important or unneeded documents and applications. That's not a bad practice, but if you find your drive getting close to 90% full (10% or less free space), then it's definitely time to install a larger drive. Once you cross the 10% threshold, OS X is no longer able to optimize disk performance by automatically defragmenting files. Keeping a nearly full hard drive can create an overall reduced performance from your Mac.

Other reasons to upgrade include increasing basic performance by installing a faster drive and reducing power consumption with newer, more energy-efficient drives. And if you're starting to have problems with a drive, you should replace it before you lose data.

Hard Drive Interface

Apple has been using SATA (Serial Advanced Technology Attachment) as a drive interface since the PowerMac G5. As a result, just about all of the Macs currently in use have SATA II or SATA III hard drives. The difference between the two is the maximum throughput (speed) of the interface. Luckily, SATA III hard drives are backward compatible with the older SATA II interface, so you don't need to concern yourself about matching the interface and drive type.

Hard Drive Physical Size

Apple uses both 3.5-inch hard drives–mainly in its desktop offerings–and 2.5-inch hard drives in its portable lineup and the Mac mini. You should stick with a drive that's the same physical size as the one you're replacing.

It's possible to install a 2.5-inch form factor drive in place of a 3.5-inch drive, but it requires an adapter.

Types of Hard Drives

The two prominent categories of drives are platter-based and solid-state. Platter-based drives are the ones we're most familiar with because they've been used in computers for data storage for a very long time. Solid-state drives, usually referred to as SSD, are relatively new. They're based on flash memory, akin to a USB drive or the memory card in a digital camera. SSDs are designed for higher performance and can have SATA interfaces, so they can work as drop-in replacements for existing hard drives. Some may also use a PCIe interface for even faster overall performance. 

SSDs have two chief advantages and two chief disadvantages over their platter-based cousins. First, they're fast. They can read and write data at very high speeds, faster than any currently available platter-based drive for the Mac. They also consume very little power, making them a great choice for notebooks or other devices that run on batteries.

Their chief disadvantages are storage size and cost. They're fast, but they're not large. Most are in the sub-1 TB range, with 512 GB or less being the norm. If you want a 1 TB SSD in a 2.5-inch form factor (the type used with a SATA III interface) be prepared to spend several hundred dollars. The 512 GBs are a better bargain, however.

But if you crave speed (and budget isn't a deciding factor), SSDs are impressive. Most SSDs use the 2.5-inch form factor, making them plug-in replacements for the early-model MacBook, MacBook Pro, MacBook Air, and Mac mini. Macs that use a 3.5-inch drive will need an adapter for proper mounting. Current model Macs make use of a PCIe interface, requiring an SSD to use a very different form factor, making the storage module more akin to a memory module than to an older hard drive.

If your Mac uses a PCIe interface for its storage, make sure the SSD you purchase is compatible with your specific Mac.

Platter-based hard drives are available in a variety of sizes and rotational speeds. Faster rotation speeds provide faster access to data. In general, Apple used 5400 RPM drives for its notebook and Mac mini lineup, and 7400 RPM drives for the iMac and older Mac Pros. You can purchase notebook hard drives that spin at the faster 7400 RPM as well as 3.5-inch drives that spin at 10,000 RPM. These faster spinning drives use more power, and generally, have smaller storage capacity, but they do provide a boost in overall performance.

Installing Hard Drives

Hard drive installation is usually pretty straightforward, though the exact procedure for accessing the hard drive itself is different for each Mac model. The Mac Pro has four drive bays that slide in and out with no tools required. The iMac or Mac mini, however, can require extensive disassembly just to get to where the hard drive is located.

Because all of the hard drives use the same SATA-based interface, the process for changing out a drive, once you gain access to it, is pretty much the same. The SATA interface uses two connectors. One's for power, and the other is for data. The cables are small and easy to connect. You can't make the wrong connection because each input is a different size and won't accept anything but the proper plug. You also don't have any jumpers to configure on SATA-based hard drives. All of these factors make changing out a SATA-based hard drive a simple process.

Heat Sensors

All Macs except the Mac Pro have temperature sensors attached to the hard drive. When you change out a drive, you need to reattach the temperature sensor to the new drive. The sensor is a tiny device attached to a separate cable.

You can usually peel the sensor off the old drive and just stick it back to the case of the new one. The exceptions are the late 2009 iMac and 2010 Mac mini, which use the hard drive's internal heat sensor. With these models, you need to replace the hard drive with one from the same manufacturer or purchase a new sensor cable to match the new drive.

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