An external drive is a storage device you plug into your computer to hold files, photos, videos, and backups outside your machine

An external drive is a hard drive or solid-state drive (SSD) housed in a protective case with a cable attached. You connect it to your computer through a USB port, Thunderbolt port, or wireless connection. The drive itself works the same way as the storage inside your computer — it reads and writes data — but because it lives outside your machine, you can unplug it, move it, or connect it to a different computer whenever you need to.

External drives come in two main types: traditional hard disk drives (HDDs), which use spinning platters to store data, and solid-state drives (SSDs), which use flash memory similar to a USB stick. HDDs tend to be cheaper and hold more data per dollar. SSDs are faster, more durable, and lighter, but cost more per gigabyte. Both types plug in the same way and work with Windows, Mac, or Linux computers.

Key Takeaways

  • External drives connect to your computer through a USB, Thunderbolt, or wireless port and store files outside your machine.
  • Hard disk drives (HDDs) are cheaper and hold more data; solid-state drives (SSDs) are faster and more durable but cost more.
  • You can use an external drive to back up your computer, move files between machines, or expand your storage without opening your computer.
  • Most external drives work with Windows and Mac computers, though you may need to reformat one if it was set up for a different operating system.
  • Connection speed depends on your cable type — USB 3.0 is standard, USB 3.1 and Thunderbolt are faster, and wireless drives are slowest.

Why people use external drives

The most common reason to buy an external drive is to back up your computer. If your computer's hard drive fails, you lose everything on it — photos, documents, financial records, everything. An external drive lets you copy your entire computer or just your most important files to a separate device. If something goes wrong with your computer, you still have a copy.

External drives also let you move large files between computers without using email or cloud storage. A video editor might move a 50-gigabyte project file from a laptop to a desktop machine by plugging in a drive. A photographer might carry thousands of photos on an external drive instead of keeping them all on their camera's memory card.

Some people use external drives to add storage space. If your computer's built-in drive is full and you do not want to delete anything, you can move older files to an external drive and keep your computer running smoothly. This is cheaper than buying a new computer with more storage.

How external drives connect to your computer

Most external drives use USB (Universal Serial Bus) cables. USB 3.0 is the standard on most computers and drives made in the last five years — it transfers data at up to 400 megabytes per second. Newer drives may use USB 3.1 or USB-C, which are faster. Older drives may use USB 2.0, which is much slower but still works on any computer with a USB port.

Some external drives use Thunderbolt cables, which are faster than USB and common on newer Mac computers. A few high-end drives use Thunderbolt 3 or Thunderbolt 4, which can transfer data at over 1,000 megabytes per second — useful if you work with very large video files or databases.

Wireless external drives connect over Wi-Fi instead of a cable. You can access files on them from anywhere in your home or office without plugging anything in. The trade-off is speed — wireless drives are much slower than wired ones, and the connection can drop if you move too far from your router.

Storage capacity and what it means

External drives come in sizes from 500 gigabytes to 20 terabytes or more. A gigabyte (GB) is roughly 1,000 megabytes. A terabyte (TB) is roughly 1,000 gigabytes. For most people, 1 to 2 terabytes is enough to back up an entire computer or store years of photos and videos. Professional video editors or data analysts might need 4 terabytes or more.

The stated capacity on the box is not the same as the usable space. A 1-terabyte drive usually shows about 930 gigabytes of usable space after the operating system and file system take their share. This is normal and not a defect.

Formatting and compatibility between Windows and Mac

External drives are formatted — prepared to work with a specific operating system — before they leave the factory. A drive formatted for Windows may not work on a Mac without reformatting, and vice versa. Some drives come pre-formatted for Windows, others for Mac, and some for both.

If you buy a drive formatted for the wrong system, you have two choices. You can reformat it to work with your computer, which erases everything on it. Or you can use software to read the drive without reformatting — this is slower and more complicated. Most people straightforward reformat. If you plan to use the same drive on both Windows and Mac computers, you can format it as exFAT, which both systems understand natively.

Speed, durability, and what to expect

An external HDD is slower than an internal drive because the data has to travel through a cable. You will notice the difference when copying large files or backing up your entire computer — it may take several hours. An external SSD is much faster and may take only 30 minutes to back up a computer, but costs more upfront.

External drives are more durable than internal ones because they have protective cases and do not spin as fast (if they are SSDs). However, they are still electronic devices that can fail. Dropping a drive, exposing it to extreme heat or cold, or leaving it plugged in during a power surge can damage it. Treat an external drive as a temporary holding place for important files, not a permanent archive — keep a second backup somewhere else if the data truly matters.

Frequently Asked Questions

Do I need to eject an external drive before unplugging it?

Yes. On Windows, right-click the drive in File Explorer and select "Eject". On Mac, drag the drive icon to the trash or right-click and select "Eject". This tells your computer to stop using the drive and close any open files. Unplugging without ejecting can corrupt files or damage the drive's file system.

Can I use an external drive to run programs or install software?

You can store programs on an external drive, but they will run slowly because data travels through the cable. Some programs also require installation files to be on your computer's main drive. For most uses, an external drive is better for storage and backups than for running software.

What is the difference between an external drive and a USB stick?

A USB stick (or thumb drive) is smaller, cheaper, and holds less data — usually 32 to 256 gigabytes. An external drive holds more data, transfers faster, and is more durable. USB sticks are good for carrying a few files between computers. External drives are better for backups and long-term storage.

How long do external drives last?

Most external drives last three to five years with normal use. HDDs may fail sooner if they are moved around a lot or exposed to heat. SSDs tend to last longer but can fail suddenly without warning. Do not rely on any single drive as your only copy of important files.

Can I use an external drive with a tablet or phone?

Some tablets and phones support external drives through USB-C or Lightning ports, but support varies by device and operating system. Android tablets are more likely to work than iPhones. Check your device's manual or the drive manufacturer's website to confirm compatibility before buying.