Computer Hard Drive

January 18, 2013 under Computer Components

A critical component of any computer today is the hard drive. The hard drive is hardware that stores data on your computer so that programs can be run and use your system’s hardware resources. Your files such as photos, videos, and music are stored on the hard drive. Computer hard drives have come a long way since their beginning. Compared to then, they can hold massive amounts of data, they are much smaller, and they are much less expensive. Really, throughout their history, their cost has continued to decrease while their storage capacity increases. This is definitely good for the consumer.

We will discuss several general topics about hard drives that will be good to know when learning computer hardware basics. These will include the main types on the market today, physical characteristics, and some of the inner workings of them.

Hard drives can be either internal or external. The most common for years now have been magnetic, SATA and PATA drives. These are very fragile, mechanical drives that are the standard in computers. Recently, however, a newer technology has started making an impact on the HDD (hard disk drive) market, Solid-State drives. We will discuss main points about both.

Magnetic Hard Drives

There are three main parts to SATA/PATA hard drives. First, the hard disk is made of platters, or disks, that store data. The second main component is the host adapter, usually found on the motherboard, which allows the computer to understand the data being transferred from the hard drive. Finally, you have the controller chip. As its name suggest, it controls the functions of the hard drive. It controls the motors that spin the discs and receives signals sent by the drive. On a semi-side note, PATA stands for Parallel Advanced Technology Attachment and uses a 40-pin connector for parallel data transfers. SATA, Serial Advanced Technology Attachment, uses a newer 7-pin connector for serial data transfer.

The inside of hard disk drives are extremely sensitive to small debris and will crash or malfunction if contaminated. Therefore, they are sealed before being sold. The circular platters need to be totally dirt and dust free for the read/write heads to extract and transfer data. The read/write head is located on a mechanical arm that moves it across one side of a platter, allowing it to find specific data addresses on the disc. This platter is closely situated near other platters to form the shape of a cylinder. One head is associated to one specific side of a platter. So if there are 3 platters in the hard drive, there will be a total of six heads. Each disc platter is divided into tracks that spiral around their surface. These tracks, in turn, are divided into sectors that can hold 512 bytes of data. The controller understands the layout of the disc and receives instructions from the BIOS when reading and writing data to and from the platters. On the other hand, the BIOS must receive information from the controller to understand the layout of the drive.

File systems are put on the tracks to group certain amounts of memory into clusters so that the hard drives can receive unique addresses for data to be stored and found. This being the case, two or more files cannot occupy one single sector. This means that once a file is using a sector, if there is still more memory in that sector that is not being used, it can never be used, due to address limitations. This inefficiency will result in data waste. This works the same way for clusters created by the file system. But since clusters are larger than sectors, even more data is wasted.

Internal Hard Drive & External Hard Drive:


Whereas the conventional disk drives discussed above are susceptible to physical damage due to their moving parts and fragility within the relationship between the heads and platters, solid-state drives have no moving parts at all. Think of a flash drive (or thumb drive/jump drive) when thinking about a SSD. These newer devices use integrated circuits to store data and are considerably faster than older magnetic disks when reading and writing data. There are several downsides to Solid-State drives at present. First, they are considerably more expensive than magnetic disk drives with less memory storage. Also, as data is accessed, it shortens the useful life of the drive itself. However, as development becomes more efficient, the pricing will decrease, and the capabilities will increase.


Those are the main computer hard drives available today. Future posts will go more in-depth about the characteristics of each. In your quest for learning computer hardware basics, continue to research on your own these components. Hard drives are complex, just as computers are. One post could not hope to cover all you can know about them.

Solid-State Hard Drive:

Source 1:
Quentin Docter, et al. CompTIA A+ Complete Study Guide. 2009

Source 2:

Source 3:
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