Choosing your Hard drive

What can i tell you about the hard drive.
A hard disk drive (often shortened as "hard disk" or "hard drive"), is a non-volatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces. Strictly speaking, "drive" refers to a device distinct from its medium, such as a tape drive and its tape, or a floppy disk drive and its floppy disk. Early HDDs had removable media; however, an HDD today is typically a sealed unit (except for a filtered vent hole to equalize air pressure) with fixed media.
That being said let's see

what you need to know before getting one.
Capacity
Connection type
data transfer rate (dtr)

Capacity
The capacity of an hard drive (hd) is the space it has to store files. Ex:500Gb,120Gb....
For the comnon use i would say at least 250gb. For gaming or movies as much as you can afford.
Back in the days it was really hard to get a 40Gb hard drive to get full. Today a 1TB (terabyte) is hardly enough for gamers and movies. Get one that suits your needs. And has a good Cost/Capacity rate.

Connection type
Depending on what motherboard you have the connection type isn't really that hard to match. Because there are few commonly today used connections types. Ex: sata, IDE,SCSI...
The most common and the best is Sata (Serial Advanced Technology Attachment) and even sata has only 3 types, they are all the same connector, but have different transfer speed rates.

Data transfer rate (dts)
As of 2008, a typical 7200rpm desktop hard drive has a sustained "disk-to-buffer" data transfer rate of about 70 megabytes per second. Data transfer rate is the speed that you can store and access data on your hard drive. Ex:if my hard drive has 30 mb/s of data transfer rate, that tells me that it would take 1 second to save a 30mb file from any device to my hard drive.

This is basically what you need to know,about choosing your hard drive.
Next up choosing the case for your components!