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The Hard Disk Drive (HDD)


Inside your hard Disk DriveThe hard disk drive is a computers main non-volatile storage device, meaning that data stored on a hard disk drive is not lost when the computer is turned off. This is where your operating system, your games and the files you create are saved before your computer is switched off. It can also be known as a hard disk or fixed disk drive. It is a sealed unit that contains one or more platters (disks) and a head very similar to a vinyl record player in the way it operates with the head floating a few thousands of an inch above the platter reading and writing in a spiral fashion accross the face of the platter. The platter or platters spin at very high speeds, anything up to 15 000rpm. The data is stored on the disk as either a 0 or a 1 by magnetizing ferromagnetic material bonded to the disk platter which has been divided into sectors in a similar fashion to the bumps and grooves on a record.

Hard drives are available in a variety of form factors, which refer to its physical size, and capacities, referring to how much data they can hold. The form factor most commonly used in PC's is the 3 1/2 inch drive and when approaching your hardware vendor the best tact is to avoid the form factor issue altogether and ask for a desktop hard drive as they will then supply a 3.5 inch drive or one of its lower profile cousins without raising concerns that you might have more unusual requirements. Choosing the capacity of your drive really becomes a question of your own needs and the intended purpose of the computer. Hard drive capacity is measured in gigabytes (GB, thousands of megabytes) with drives smaller in capacity than 120GB becoming scarce on the ground and larger drives reaching the 1000GB (1 terabyte) mark. If the machine is to be used for word processing then a 1 terabyte hard disk drive is of little benefit.

Hard drives must be connected to the computers motherboard by some method of course to work correctly and there are a number of different bus types to accommodate this including ATA (Parallel ATA, also commonly called IDE or EIDE), Serial ATA (most commonly called SATA), SCSI and fibre channel. IDE (pronounced eye-dee-e) or SATA (pronounced sah-tah) are by far the most commonly used in personal computers and will be the ones documented on this web site.

Comparing IDE and SATA hard drives.
If you examine the ribbon cable that plugs into your IDE connector on the drive you will see that it has three connectors on it and down one side of the cable there is a stripe, usually red, on the edge. This stripe corresponds with PIN 1 on the IDE connector and is there to make sure the cable is correctly oriented when plugged in. Usually the the connectors will also have a key and slot to make sure they are plugged in correctly. If this is not the case then pin one is the top right hand corner pin when looking at the connector face on. With the three connectors, one of course plugs into the motherboard and the other two connect to a hard drive, optical drive or other storage device so you can have two devices on one IDE channel. If you are using two devices on the IDE channel (on one cable) one must be jumpered to be a master and the other a slave or they will not work. This is not as complicated as it might sound although it does require a bit of planning if you have many drives to plug into your computer. If you have two IDE connectors on your motherboard consider putting your devices on different channels if you only have two of them, say one hard disk and a DVD burner. This will give a slight increase in speed when copying from one to the other. Finally, there is the power connector which provides power from the power supply to the drive. Simply plug it in.

Connecting a Serial ATA hard disk drive drive is much easier. Master or slave is not specified on SATA so it is a simple case of plugging in the data connector (the smaller connector) into the drive and the other end of the data cable into a spare SATA port on your mainboard. The power connector is the larger of the two connectors and you may need an adaptor to convert the SATA power cable to a standard molex connector that is used on most power supplies. With newer model power supplies this is not necessary as they have the appropriate connector but when buying a PC in components it is wise to check if the adaptor is necessary as it will save you a trip back to your computer shop.