A chunk of data is called a “bit.” This is the smallest unit of information. Even the most complex computers make use of binary bit combinations of 0 and 1. These strings of bits are the basic components of everything from text and pictures to music.
When two bits are combined they become bytes. There are 8 bits to a byte, allowing 256 possible combinations that allow the creation of letters, numbers, spaces, punctuation and other extended characters. Therefore, a sentence made up of 125 characters (including punctation marks and spaces) has 125 bytes. Some files will also include formatting data, which also take up bytes.
A typical page in a word program (the equivalent of typing something on short bond paper) will measure about 2 kilobytes. A megabyte would hold about 500 pages, the equivalent of a thick book. A gigabyte could hold half a million pages or 1,000 thick books. Meanwhile a terabyte would have more text capacity than most libraries—a million thick books.
A petabyte, on the other hand, holds as many books as one would find in 180 libraries of congress, the world’s largest library (with over 28 million volumes within its walls). That’s a lot of information. And an Exabyte would hold the equivalent of 180,000 libraries of congress.
A typical compact disk has the capacity of 750 megabytes. If this disk were to contain just text, that would be the equivalent of 375,000 pages. Imagine then the capacity of 4.7 gigabyte DVD’s. One could hold about 2.3 million pages. A Blu-Ray disk could hold the text equivalent of approximately 67,500 books.