78. Parts of a Computer - 3. The Hard Drive

A typical HDD from a desktop PC

What is a Hard Disk Drive?
The hard disk drive is the main, and usually largest, data storage hardware device in a computer.

The operating system, software titles and most other files are stored in the hard disk drive.

The Hard Disk Drive is Also Known As
HDD (abbreviation), hard drive, hard disk, fixed drive, fixed disk, fixed disk drive

Important Hard Disk Drive Facts
The hard drive is sometimes referred to as the "C drive" due to the fact that Microsoft Windows designates the "C" drive letter to the primary partition on the primary hard drive in a computer by default.

While this is not a technically correct term to use, it is still common. For example, some computers have multiple drive letters (e.g. C, D, E) representing areas across one or more hard drives.

Popular Hard Disk Drive Manufacturers
 Seagate, Western Digital, Hitachi

Hard Disk Drive Description
 

HDD from a laptop

A hard drive in a desktop or tower PC is usually the size of a paperback book but much heavier. Nowadays inside laptop (or notebook PCs) there are choices to be made between Solid State Drives known as SSDs, or normal drives which are a lot smaller than their big brothers inside the desktops. Smaller means in dimension only as their capacity can be up to 3TB. SSDs are still expensive compared to those with moving parts but they are reputedly
quicker on start up and run more quietly as they have no fans or moving parts.

The sides of the hard drive have pre drilled, threaded holes for easy mounting in the 3.5 inch drive bay in the computer case. Mounting is also possible in a larger 5.25 inch drive bay with an adapter. The hard drive is mounted so the end with the connections faces inside the computer.

The back end of the hard drive contains a port for a cable that connects to the motherboard. The type of cable used will depend on the type of drive but is almost always included with a hard drive purchase. Also here is a connection for power from the power supply.

Most hard drives also have jumper settings on the back end that define how the motherboard is to recognize the drive when more than one is present. These settings vary from drive to drive so check with your hard drive manufacturer for details.

Hard drives contain platters inside which spin at over 5,000 rpm. They are delicate little beasts and are prone to damage if jolted or dropped. ALWAYS HAVE YOUR DRIVES BACKED UP. They are hermetically sealed to prevent the ingress of dust or smoke etc.

Comparison of common particles to the head-gap

A Head Crash occurs when the read-write head hovering over the platter touches the platter itself. If that happens the HDD is usually ruined and has to be replaced. This diagram shows the relative thicknesses of a smoke particle, a human hair, and a dust particle compared to the gap between the read-write head and the coated surface of the platter. Crashes are usually caused by moving the drive whilst it is in motion, or dropping it as can happen with external drives.

Inserting a laptop HDD into a caddy

If you change the HDD inside your PC but it is still useable, say you have upgraded to a larger HDD, then the removed disk may be used inside a caddy which will house the disk and allow its use as an external drive for extra storage or backups of essential parts of your data. Here you can see a small caddy (Usual cost between 6 and 10 euros) being used to house a laptop HDD for external use. Small-form HDDs will be powered via the USB port on your PC whereas the larger disks removed from desktop machines require power from an adaptor plugged into the mains. Cables and power supplies always come with the purchase of caddies which are very easy to use.

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