Hard drive buying guide

We walk you through the process of buying a new hard drive, and explain all the jargon: from network-attached storage to solid-stated drives

Hard drives can be found in all sorts of products — PCs, digital video recorders (DVR), camcorders and MP3 players, for example. The hard drive is one of the most important components for PCs, as it provides permanent, large-scale storage for a user's documents, pictures, videos and other data.It's also where the operating system and programs are stored. Unlike memory (RAM), hard drives retain information even when the PC is powered off.

If you're buying or building a new PC, or have simply run out of space on your existing PC and need to boost your storage capacity, knowing what to look for in a hard disk is vital.

How do hard drives work?

First employed commercially in the 1950s, a conventional hard disk comprises one or more circular platters of magnetic material, with billions of microscopic magnetic domains, each representing one bit of data. These zones are embedded into concentric circles, called tracks. A read/write head floats above the tracks, and the magnetic flux patterns of the zones affects an electric current flowing through the head, which in turn registers as a "0" or a "1" to the drive's electronics. The head can also alter the magnetic patterns, to write data onto the disk.

When in operation, an electric motor spins the hard disk constantly, rather like an LP or CD, in order to bring the data on the tracks around to the head. The head moves across the surface of the disk, to position it above the track on which the desired data is stored. The head will then wait for the rotation of the disk to bring the data around.

A "hard disk", as we understand it today, will usually comprise multiple platters (typically between two to four in a standard consumer hard disk). Modern hard disks can vary in size from 1in wide for smaller personal media players to the more commonly available 3.5in hard drives for desktop computers.

What is a solid-state drive?

A recent trend in the storage market has seen a slow shift toward a new type of permanent storage: the solid-state drive (SSD). Unlike hard drives, which have moving parts and are more prone to being damaged if dropped or bumped, solid-state drives don't need magnetic plates and hard drive heads.

These drives work by employing solid-state SRAM or DRAM memory to store information, like the memory modules which make up the RAM in a computer. However, unlike RAM, which loses its stored information every time a computer restarts or shuts down, an SSD uses non-volatile memory.

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