An external hard drive is a portable storage device that can be attached to a computer via USB connection or wirelessly. It provides additional storage space for backing up important files like documents, photos, videos, and music. Unlike the internal hard drive installed inside a computer, external hard drives can usually be unplugged, moved and used with different computers. The main purposes of using an external drive are for backup, archiving, expanding storage capacity or transferring files between computers.
External hard drives come in different storage capacities and can be a plug-and-play storage solution for home computer users. They don’t require installation inside a computer case and are very easy to set up. Most external hard drives just need to be plugged into the computer for you to start storing, backing up and transferring files. Key advantages are portability, ease of use and flexibility in storage capacity.
Hard Drive Speed Basics
The two main factors that determine an external hard drive’s speed are the rotational speed (RPM) and the data transfer rate.
The rotational speed, measured in revolutions per minute (RPM), refers to how fast the platters inside the hard drive spin. Common speeds for external hard drives range from 5,400 RPM on the low end to 10,000 RPM on the high end, with 7,200 RPM being the most common.
Faster rotational speeds allow the read/write heads to access data quicker. So a 10,000 RPM drive can read and write data faster than a 5,400 RPM drive. According to Buildcomputers.net, going from 5,400 RPM to 7,200 RPM offers about a 20% increase in speed, while going from 7,200 RPM to 10,000 RPM offers a 30% speed boost.
The data transfer rate determines how fast data can move between the external drive and computer. It’s measured in megabytes per second (MB/s) for read and write speeds. Many external HDDs today have maximum data transfer rates of 100-130 MB/s over USB 3.0.
Major Factors in External HDD Speeds
There are three major factors that affect the speed of an external hard drive:
Interface
The interface of the external HDD plays a big role in determining the maximum transfer speed. Common interfaces include USB 2.0, USB 3.0, USB 3.1, USB-C, Thunderbolt, eSATA, and FireWire. The faster the interface technology, the higher the potential transfer speed. For example, USB 2.0 has a max speed of 60MB/s, while USB 3.1 can reach 10 Gbps (around 1,250 MB/s). Thunderbolt 3 has a blazing fast max speed of 40 Gbps.1
RPM Speed
The rotational speed of the hard disk platter, measured in revolutions per minute (RPM), also affects transfer rate. Most external drives today use either 5,400 RPM or 7,200 RPM. 7,200 RPM drives are generally faster than 5,400 RPM drives, but use more power and run hotter.2
Cache Size
The cache acts as high-speed temporary storage between the drive and computer. Larger cache sizes generally result in faster transfer speeds. For example, an 8MB cache typically performs better than a 2MB cache. However, the performance boost diminishes beyond 32MB.3
Common External HDD Interfaces
There are several common interfaces used for external hard drives that affect speed and performance:
USB 2.0
USB 2.0 is an older, slower USB standard that offers speeds up to 480 Mbps. Many cheaper external drives still use USB 2.0, but it limits performance compared to newer interfaces.
USB 3.0/3.1
USB 3.0 and 3.1 offer major speed improvements over USB 2.0. USB 3.0 provides up to 5 Gbps, while USB 3.1 reaches 10 Gbps. Most modern external HDDs use one of these interfaces.
USB-C
USB-C is a connector shape that supports USB 3.1 and Thunderbolt 3. USB-C allows for slimmer, more portable HDD designs. The interface itself does not determine speed – an external HDD can use USB-C with USB 3.1 or Thunderbolt 3.
Thunderbolt 3
Thunderbolt 3 offers the fastest interface commonly available, reaching speeds up to 40 Gbps. However, Thunderbolt-equipped drives have a higher cost.
eSATA
eSATA provides fast speeds up to 6 Gbps, but requires an eSATA port on your computer. It is not as widely adopted as USB interfaces.
RPM Speeds
The rotational speed of a hard drive, measured in revolutions per minute (RPM), is one of the major factors that impacts performance. Higher RPM generally means faster access times and data transfer speeds.
Most external hard drives today use either 5400 RPM or 7200 RPM. 5400 RPM drives are more common and affordable, while 7200 RPM drives are faster but run hotter and consume more power. There are also high-performance 10,000+ RPM drives, but these are less common for external storage.
A 5400 RPM drive offers average read/write speeds of around 100 MB/s, while a 7200 RPM drive is about 33% faster. So for large file transfers or gaming, a 7200 RPM drive provides a noticeable speed boost over 5400 RPM. But for basic backups or media storage, a 5400 RPM drive is usually sufficient.
10,000+ RPM drives can reach over 200 MB/s speeds, but most consumer applications don’t require this level of performance. These ultra high-RPM drives are more common for enterprise servers or high-end workstations.
Cache Size
The cache on a hard drive is a small amount of high speed memory that acts as a buffer between the drive’s main components. This cache holds frequently accessed data, which allows the hard drive to access this data faster than if it had to physically locate it on the disk each time. The larger the cache, the more data it can hold, generally resulting in better performance.
Most external hard drives today come with 8MB, 16MB, 32MB or even 64MB of cache. But do these differences actually impact real world performance?
Overall, larger cache sizes do provide a performance benefit, especially for use cases involving heavy disk access like gaming or video editing. However, the impact is incremental and diminishes with larger sizes. For example, upgrading from 8MB to 16MB of cache will be more noticeable than going from 32MB to 64MB. According to one analysis, the difference between 32MB and 64MB of cache only results in a 1-3% performance increase.[1]
For general external storage uses like backup, media storage or light office work, most users will not notice major speed differences between cache sizes. But gamers or power users working with large files may want to opt for 32MB or 64MB of cache to maximize performance.
[1] https://www.pcguide.com/hdd/guide/hard-drive-cache/
Real-World Speed Differences
External hard drives with SSDs (solid-state drives) provide substantially faster real-world speeds compared to HDDs (hard disk drives) according to testing and reviews. For example, benchmarks by PCMag showed the SanDisk Extreme Portable SSD with real-world transfers up to 550MB/s read and 500MB/s write, whereas an external HDD like the WD My Passport managed 130MB/s read and 125MB/s write at its fastest.
SSD external drives have the advantage for common use cases like transferring large files, loading games, editing videos, and working with photos. The higher speeds allow SSDs to transfer multi-gigabyte files in seconds rather than minutes needed for HDDs. For backup or storage of infrequently accessed data, HDDs provide more storage capacity for lower cost, but with slower transfer speeds.
Max Speeds by Interface
There can be a big difference between the theoretical maximum speeds of an interface like USB 3.0 vs USB-C and the real-world speeds you’ll actually achieve. This is due to protocol overhead and other factors.
USB 3.0 has a theoretical maximum speed of 5 Gbps (640 MB/s), while USB 3.1 Gen 2 and USB-C top out at 10 Gbps (1,250 MB/s). However, real-world USB 3.0 speeds tend to be around 400 MB/s at best, with USB-C hitting around 500-600 MB/s.
As one example, a USB 3.0 external SSD may be capable of Read speeds over 400 MB/s and Write speeds over 300 MB/s. Upgrading to a USB-C SSD can boost that to 550/500 MB/s for Reads/Writes.
So while USB-C offers significantly higher potential bandwidth, the real-world speed gains are typically more modest. Still, USB-C is faster overall and continues to improve.
Sources:
https://monopricesupport.kayako.com/article/128-how-much-faster-is-usb-c-compared-to-previous-generations-of-usb-to-sata-and-to-thunderbolt
Recommendations
In general, higher speeds provide better performance, especially for activities like transferring large files or running programs off the external drive. According to Digital Trends, if you plan to edit video or lots of images directly from the external drive, opt for an SSD or 7200 RPM drive for the best speeds.
For backup or basic storage purposes, a 5400 RPM drive is likely sufficient. The speed difference may only amount to seconds in many cases. As Seagate notes, a 5400 RPM drive can handle streaming music or videos just fine.
When shopping for an external HDD, consider what you plan to use it for. If you need to frequently transfer large files or run programs from the drive, spring for a faster SSD or high RPM HDD. But for backups and basic storage, a standard 5400 RPM drive offers decent speeds at a lower cost.
Conclusion
In summary, external hard drives do indeed have varying speeds depending on several key factors. The main factors that impact speed are the HDD’s interface type, RPM speed, and cache size. SATA III offers the fastest maximum interface speeds, while USB 2.0 is much slower. In terms of RPM speeds, 7200 RPM drives are the fastest, with 5400 RPM being standard and acceptable speeds. For cache, 32 MB or 64 MB is ideal for good performance. Overall, an external HDD with a SATA III interface, 7200 RPM speed, and at least 32 MB cache will provide the fastest speeds. However, even USB 3.0 or Thunderbolt drives with 5400 RPM and lower cache sizes can still offer decent speeds for many users’ needs.
In conclusion, it’s recommended to get a drive with USB 3.0 at a minimum if speed is a priority, along with aiming for 7200 RPM if possible. Checking the cache size should also be considered. Going with a higher-end SATA III interface drive offers maximum speed potential, but may be overkill for some users. When shopping for an external HDD, looking at the interface, RPM speed, and cache size will give you an idea of the relative real-world speeds you can expect.
