For some of us, either name means the same and for others, it is only about the material used to make either medium and their storage capacity. You may be right with either thought depending on the region you are from and prior knowledge you have devoured already. Pointing out the fundamental differences is key here. The confusion arising from these two terminologies is as adamant as a blood thirsty mosquito. That adamant! Time to exterminate the persistent bug; read through as I demystify the key differences in the underlying technologies.
The first key difference you shall note is the naming of the two. One is a disc while the other is a disk. The pronunciation is the same, the spelling is different. The distinct c and k ideally symbolise some difference no doubt but is this difference the technologies used with both storage medium? The simple answer is no. The actual answer… read on.
This fundamental difference comes from grammar believe it or not. English is the reasons why we have these two distinct storage medium. Science is not the reason and most definitely, computer science is not the culprit. The first step is to define the word disk and then move on from there.
The general definition of a disk is a round plate on which data can be encoded. That basically fits the description of a hard disk (if you have ever disassembled one) and an optical disk. The k on the optical disk is not a typo. There are two broad categories of disks, the first being magnetic and the second being optical. Some popular types of magnetic disks include the floppy disk and the hard disk. For optical discs, we have the CD-ROM, CD-RW and the CD-R. Expounding the differences between the optics and magnets is going to play a fundamental role in making you understand these concepts even better.
The Optical Disc
There are many forms of discs out there… not the flying saucer type though. The disc in scope is the Compact Disc since it shall form the basis of our definition. Let us start off with defining a disc, the optical disc. By definition, an optical disc is a flat, circular disc that encodes binary data in form of pits and lands on a special material on one of its sides. Now, English tells us that a disc is a flat, thin circular object. Binary in computing means 1’s and 0’s. Pits represent 0’s and lands represent 1’s. In the case of the optical disc, 0 means that there is no reflections when light hits a spot on that disc and 1 means there is reflection. Data is encoded through a spiral path from the interior to the exterior of the disc. Now that that is out of the way, lets disassemble the disk. Note; key technology in the optical disc is optics – to do with the study and behaviour or light.
The Hard Disk
This one is a bit different from the CD. The hard disk is an electromechanical (utilising electricity and mechanics) data storage device that uses magnetic storage to store and retrieve digital data using one or more discs coated with a magnetic material. To write to and read data from the discs, magnetic heads are used. Unlike the CD’s, the data is not stored sequentially or in a spiral format. It is stored in a random fashion and that means that data can be access in whatever order in form of blocks. Data is recorded onto the disk by magnetising a special kind of thin film on the disc. To represent bits, the direction of magnetisation is sequentially changed. Once data is recorded, it has to be read. To do this, the magnetised heads detect the transitions in magnetisation. I won’t go into the details of how this type of disc works but you get the picture.
So, where does the difference come from?
Just like I mentioned earlier, the difference comes from grammar. Although over time some standards have been defined, which I shall briefly mention, the initial difference arose from the American spelling of the same word with a c and the British spelling with a k. The use of the two spellings have over time been compartmentalised into different fields. In the fields of music (music albums specifically) and medicine tend to use the letter c, while the field of computing tends to use the letter k. Both can be used interchangeably. In the present and recent past, the word disc has been generalised as disks that use optical technology while the word disk has been used to mean disks that use electromagnetic and mechanical phenomenon.
Now you know.