An essential complement to any computer, the external hard drive not only extends the storage capacity of a PC or Mac, but also, and above all, archives files to protect them and transport them in order to copy them to another machine. Combined with data encryption software, it can even serve as an electronic safe by protecting confidential information. In the event of a breakdown or loss of the computer, it is thus possible to find all the precious files.
First of all, it should be noted that hard drives are not confined to a single operating system: regardless of the file format in which they are sold (FAT32, NTFS, etc.), they can be reformatted to use them indifferently under Windows macOS, Linux or even with game consoles. External hard drives are also very useful with connected televisions, which all have at least one USB socket. You can indeed store videos, photos and music there to play them with the multimedia player integrated into the screen, without having to go through the network or an online service. You can keep hundreds of files in a miniature format.
Strong competition from external SSDs (flash memory electronic storage systems) in recent years, external mechanical hard drives (HDD) are more fragile and slower. But they still have several advantages: they are cheaper while having a higher storage capacity. Additionally, unlike SSDs and Flash memory-based systems in general, they support a near-infinite number of write and read cycles, making them more future-proof.
The capacity of an external hard drive directly affects its price. The most common models range from 500 GB to 2 TB, but there are disks going beyond (4, 6, 8 and even 10 TB). Be careful, manufacturers and merchants systematically indicate the raw capacity, before formatting: the space actually available for file storage is always less than that announced (sometimes it takes 10% less).
Most current external hard drives connect to a computer via a USB interface. The latest models are compatible with USB 3.1, with reversible Type-C connectors, which offers a transfer speed of 5 to 10 Gbit/s. USB 2.0 (480 Mbit/s) models are tending to disappear and are to be reserved for occasional use, which does not require fast transfer. On Mac, there are Thunderbolt interfaces, with USB Type-C connectors, offering a transfer speed of 40 Gbit/s (for Thunderbolt 3.0). Other interfaces exist, such as e-Sata, which offers a speed of 6 Gbit/s: but this type of interface remains very rare on computers.
On a technical level, the flow rate is also linked to the rotation speed of the magnetic disk platters (5400 rpm for the slowest, 7200 rpm for the fastest). Please note, most USB 3.0 models use a specific cable, with a micro-B USB 3 type male connector on one side and a type A connector on the other: there is therefore no question of connecting them with a standard USB cable in case oblivion or loss.
There are mainly two types of external hard drives: portable and fixed, also called “desktop”. Incorporating miniature hard drives in 2.5-inch format, the first are compact (the equivalent of a wallet) and light: they are very easy to transport and are powered directly via USB. You can easily take them on a trip, slipping them into a pocket or a satchel. Desktop models use conventional 3.5-inch drives. Larger and heavier, they have a capacity and performance superior to portable models, but often have to be plugged into the mains via an adapter (supplied), which makes their use more restrictive.
Finally, note that there are external hard drives with a Wi-Fi interface to extend the storage space of any type of device (smartphone, tablet, PC, etc.) wirelessly. Throughput isn’t as high as with a wired connection, but it’s usually enough to play files without having to copy them to another device.