This overall score is made up of performance score (70%) and ease of use score (30%). 

Performance makes up 70% of the overall score. We transfer 20GB worth of large files (movie files) and 20GB worth of small files (photos, music, and office documents), and record the read and write speeds. Units with two connector options (USB Type-A and USB Type-C) are tested using both connectors.

Ease of use makes up 30% of the overall score and comprises an assessment of hardware installation (30%), design advantages/disadvantages (20%), overall style (20%) and software installation (30%).

Software Versatility score is made up of backup (50%), security (40%) and Power Management(10%) support, but is not included in the overall score.

Real-time throughput is averaged over multiple runs of transferring data sets (large and small files) to and from each drive. Megabytes (MB) were used in the results figures because this is usually the measurement used on packaging.

Real-time throughput is averaged over multiple runs of transferring data sets (large and small files) to and from each drive. Megabytes (MB) were used in the results figures because this is usually the measurement used on packaging.

We recommend USB flash drives and solid state drives with a score of 80% and above. For scores within the hard drive category we also took price into account, combining the highest score with the lowest cost.

As of July 2020.

USB flash drive (thumb drive), solid state drive (SSD), or portable hard drive (HD).

The cost of the drive divided by the number of gigabytes, to give a cost-per-gigabyte $ figure.

Storage capacity in gigabytes (GB). One terabyte (TB) is equivalent to 1000 gigabytes.

Does it include access to cloud storage for synchronising or backing up data. 

Depth x width x height.

The "USB-A" style rectangular plug is used on both USB 2.0 and USB 3.0 devices, and is still very common on USB 3.2 Gen-1 devices and many computers. The smaller round-ended Type-C plug is use for USB 3.1 Gen-1 (5Gbps) and Gen-2 (10Gbps) and Thunderbolt 3 (40Gbps) devices.

The USB-C connection is a small, round-ended reversible plug that is designed to replace the older USB-A standard. It's common on USB 3.2 Gen-1 (5Gbps) and USB 3.2 Gen-2 (10Gbps) devices, as well as newer laptops, mobile devices and computers and also used for Thunderbolt 3 (40Gbps) connections.

Whether a USB Type-A (rectangular plug) cable is included with the drive.

Has rectangular USB Type-A port for USB 3.0 or 3.2 (Gen-1) connection with speed up to 5Gbps (gigabits per second).

Has USB Type-C port for USB 3.2 (Gen-1) with speed up to 5Gbps (gigabits per second).

Has USB Type-C port for USB 3.2 (Gen-2) with speed up to 10Gbps (gigabits per second)

Has USB Type-C port for Thunderbolt 3 with speed up to 40Gbps (gigabits per second) plus up to 100W power and DisplayPort support.

Common storage drive formats include: NTFS (for PCs) – the most common and efficient format for large volumes on Windows and Linux. HFS+ (for Mac-specific drives). FAT32 – can be used across Windows and macOS/OS X platforms, but has file size and volume limitations. Ex-FAT – can be used on both platforms without the limitations of FAT32.

Note that drives within a family from the same maker may have similar model numbers to designate differences in such things as colour, capacity, casing or connectors.

Sleep timer is present in WD Drive Utilities after you install WD Discovery software. 

Some makers provide hardware-based encryption to protect your data from prying eyes. Hardware encryption is generally considered to be superior to software-based encryption, but in either case an up-to-date backup is vital as a hardware failure can prevent access to all your data. Likewise, losing the password can prevent future access.

Some makers provide software on the drive to enable encryption for protecting your data from prying eyes. Hardware encryption is generally considered to be superior to software-based encryption, but in either case an up-to-date backup is vital as a hardware failure can prevent access to all your data. Likewise, losing the password can prevent future access.

Backs up all files and folders on the drive. The massive capacity of external hard drives means an up-to-date backup is essential. Many drives will include backup software, but you don’t have to use it if you already have backup software on your PC.

Creates a full snapshot drive "image" of the entire volume including all software and files. Many drives will include backup software that will back up all files, but it may not create a full disk image for easy restoration of the entire drive and all contents.

Some drives work on a Mac straight out of the box (this should be indicated on the packaging) either by being formatted for macOS or being in a compatible cross-platform format such as exFAT. Some drives may be formated as NTFS and thus require reformatting for Mac use, or have utility software supplied so as to not require reformatting.