External hard drives and SSDs predominantly use USB 3.0 and USB 3.1 interfaces to connect to computers and other devices. Most modern external drives use one of these USB standards to take advantage of faster data transfer speeds compared to older USB 2.0. In this article, we’ll provide a quick overview of the different USB standards used by external drives and discuss their speed and compatibility.
USB 2.0
USB 2.0 was introduced in 2000 and can transfer data at speeds up to 480 Mbps. For many years, it was the standard interface used by external storage drives. However, USB 2.0 is limited by its slow max speed, especially compared to the speeds of more modern internal SSDs and HDDs. It’s not well-suited for transferring large files or backups quickly.
USB 2.0 has a maximum cable length of 5 meters. It’s also backward compatible with USB 1.1. Any computer or device that has a standard USB-A port will support USB 2.0.
While USB 2.0 is still found on some cheaper external drives today, it’s too slow for most users’ needs. Faster interfaces have largely replaced USB 2.0 on quality external storage drives.
USB 3.0
USB 3.0, sometimes referred to as USB 3.1 Gen 1, was introduced in 2008. It has a maximum theoretical transfer speed of 5 Gbps, over 10 times faster than USB 2.0. USB 3.0 cables and ports use blue color coding.
With up to 5Gbps speeds, USB 3.0 is fast enough to allow external HDDs and SSDs to transfer files at speeds similar to their max SATA interface speeds. This allows you to take full advantage of the storage device’s capabilities.
Most external drives today utilize USB 3.0 since it strikes a good balance between speed, cost, and backwards compatibility. Almost every computer and device manufactured in the last 5-10 years has USB 3.0 ports.
USB 3.1
USB 3.1, also known as USB 3.1 Gen 2, was introduced in 2013. It doubles the maximum theoretical transfer speeds of USB 3.0 to 10 Gbps. This matches the speed of the first generation of SATA Express drives.
To achieve these faster speeds, USB 3.1 requires the use of a USB-C connector and cable. USB 3.1 is backward compatible with USB 3.0 and USB 2.0 using adapters. However, both the computer connection and external drive need to support USB 3.1 to reach 10 Gbps transfer speeds.
Only some very high performance external drives leverage USB 3.1. The interface provides little benefit for traditional hard drives, which max out at around 150 MB/s transfers. USB 3.1 is more useful for external SSDs to eliminate interface bottlenecks.
Thunderbolt 3
Thunderbolt 3 isn’t technically a version of USB, but uses the same USB-C connector. Thunderbolt 3 has a maximum throughput of 40 Gbps using PCI Express (PCIe), 8 times faster than USB 3.1.
Due to the added complexity and costs, Thunderbolt 3 is generally only found on high-end external drives from vendors like Western Digital and LaCie. The interface allows extremely fast transfer speeds, which high-end creative professionals and Mac users typically value.
Thunderbolt 3 is backwards compatible with USB 3.1, USB 3.0, USB 2.0, and Thunderbolt 1/2. However, both the computer connection and external drive need Thunderbolt 3 support to achieve 40 Gbps speeds.
Compatibility
When looking at external drives, compatibility is an important consideration. You want to make sure the drive’s interface works with your computer or device’s ports. Here are some tips:
- Any external drive with USB 3.0 can plug into a USB 2.0 port. However, transfer speeds will be limited to USB 2.0’s max.
- USB 3.1 Gen 2 devices can plug into USB 3.1 Gen 1 and USB 3.0 ports using adapters. Again, speeds will be limited to the max of the host port.
- For full USB 3.1 Gen 2 speeds, both the drive and computer connection must support it.
- All Thunderbolt 1, 2, and 3 devices can plug into any Thunderbolt port, but speeds are limited to the slowest device.
- Thunderbolt 3 devices can connect to USB-C ports, but limited to USB 3.1 speeds unless the port supports Thunderbolt 3 too.
With the variety of USB standards used by external drives, backward compatibility is excellent. But you need matched devices and connections to maximize the transfer speeds.
Conclusion
Most external hard drives and SSDs today leverage either USB 3.0 or USB 3.1 interfaces. USB 3.0 offers nearly universal compatibility with speeds up to 5Gbps, fast enough for typical hard drives. USB 3.1 boosts this to 10Gbps, ideal for high-performance SSDs. Thunderbolt 3 pushes speeds even further to 40Gbps, but has less compatibility.
As long as your computer or device has a USB 3.0 or 3.1 port, you should be able to connect any modern external drive. Just be aware of the speed limitations if you use an older standard like USB 2.0.
