Megabytes (MBs) are collections of digital information. The term commonly refers to two different numbers of bytes, where each byte contains eight bits. The first definition of megabyte, used mainly in the context of computer memory, denotes 1 048 576, or 220 bytes. The other definition, used in most networking and computer storage applications, means 1 000 000, or 106 bytes. Using either definition, a megabyte is roughly the file size of a 500-page e-book.
The word bit is from binary digit. They are "yes or no" answers to unambiguous questions and are stored in computers as either zeroes or ones. Whether a door is locked is an example of a question that can be answered with only one bit. This is fundamentally how all digital information is stored in telecommunications and computing.
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Computers can use multiple bits together to store complex information. It takes at least five bits to designate one of the 26 letters in the Latin alphabet (2×2×2×2×2 = 32). The way a computer would store a letter goes something like this: bit number one designates if the letter is in the fist half of the alphabet, bit number two narrows the remaining letters into two halves, and so on. After five bits, any letter can be identified.
Today, a byte most commonly means a collection of eight bits, although the number has varied in the past. Eight bits is a convenient number of bits for storing a single character; in addition to the letter itself, format data such as capitalization is commonly stored. Information is rarely stored in bits alone — the byte is the standard unit of information addressed in computer architectures.
The confusion regarding megabytes comes from the way bytes are multiplied. Computers use binary number systems rather than decimal, or base-10, number systems. From this standpoint, it makes more sense to group bytes based on powers of two; hence the 220 definition of a megabyte. Recently, there has been a movement to use prefix definitions consistent with the metric measurement system. This would favor the 106 definition for a megabyte.
Megabytes are common file sizes in personal computing and business transactions. Text documents are often less than one megabyte in size. Images, especially from high-resolution digital cameras, commonly take up several megabytes of storage space. Movie-length video files can be larger than 1,000 megabytes. Compact disc read-only memories (CD-ROMs) generally can hold about 700 megabytes, while digital video discs (DVDs) often have capacities of several thousand megabytes.