The hard-drive is possibly the most commonly known component, and the most common one to be mistakenly identified. A very common misconception amongst many of the people we deal with is that they refer to the 'tower' (the case containing the other components) as the hard-drive.
Your hard drive is in fact a much smaller component, rectangular in shape and generally positioned towards the front of the inside of the case. The hard drive serves a very important purpose. Everything that is saved to your computer - operating systems, programs, pictures, music, videos, you name it - it's all saved on this little rectangular device in one form or another. Which is why a hard drive crash can be catastrophically distressing for some people. When it goes, everything on it often goes with it.
If you look toward the right hand side of this image (the right side is the front of the case) you will notice that around the middle there are two cartridges (this particular system has two hard-drives), that sit within a metal casing and are connected by a green circuit board beneath them.
Connected to that circuit board you will notice two flat red cables (called Serial ATA or SATA cables) which transfer the data back and forth between the hard-drives and the motherboard. You may also notice the red, yellow, and 2 black wires, that join in a plug and connect to the green circuit board. This is a power conduit through which the hard-drives receive their power supply.
There are a couple of different types of hard-drive and not all hard drive set-ups will look the same. They can be mounted in different positions, with or without casings, and may have some different connections.
The two main types of hard drive are IDE and SATA, which refer to the type of data cable used to connect them to the motherboard, and the manner and speed in which that data is transferred. Most hard drives still share the same power connector, however the data port between the types is different.
The older of the two drive types, seen above, is known as an IDE drive. It can be easily identified by the two long, parallel rows of pins that make up the connector for the IDE data cable. The data cable used for IDE drives is a 'ribbon like' cable, broad but flat, and is most commonly grey in colour, however this colour can vary.
You may also notice the power connector and jumper pins on the device, which also appear on the SATA drives as well. Standard power plugs can be connected directly from the power supply unit into the hard drive via the power connector. Jumper pins are used to select the desired behaviour of a hard drive when it is used in conjunction with another similar device. If you want one drive to act as the master while the other acts as a slave, this can be set by moving the tiny jumper to the corresponding pin position.
Much like the IDE drives, Serial ATA (SATA) drives can be identified most easily by their data ports. Unlike the IDE drives, SATA devices have flat connectors with a small right-angle hook at one end as can be seen in the image above.
The data cable for the SATA devices is also flat, however it is not nearly as broad. They are most commonly red in colour, however there are some exceptions to this.
Above is an example of a typical IDE data cable. Notice the 'ribbon like' design. You may also notice that between the two end connectors, there is another connector along the cable. This connector can be used to connect a second device to the motherboard via the one cable.
Above is a typical SATA cable. This cable is superior in data transfer in that it is significantly faster, however SATA cables can only be used to connect a single device.