What does megabyte mean?

The megabyte is a unit of digital information, denoted by the symbol MB. In the International System of Units (SI), the prefix “mega” represents a multiplier of 1,000,000 (10^6). Hence, one megabyte is equivalent to one million bytes of information, and this definition is now an integral part of the International System of Quantities.

However, in the computer and information technology fields, alternative definitions have been utilized due to historical convenience. One common usage designates a megabyte as 1,048,576 bytes (2^20 B), which conveniently aligns with the binary architecture of digital computer memory. This definition has been deprecated by standards bodies in favor of a new set of binary prefixes. The unit “mebibyte” (MiB) is now used to represent this specific quantity of 1,048,576 bytes.

If you want a more detailed explanation on the diference between a mebibyte and a megabyte, check out this article: What is the difference between MB and MiB?

Definitions

The unit “megabyte” is commonly used to refer to two different quantities: 1,000,000 bytes or 1,048,576 bytes. The latter interpretation, based on using base 1024, originated as technical jargon to represent byte multiples using powers of 2 without a specific term. Since 1024 is close to 1000, which aligns with the SI prefix “kilo-,” it became a convenient way to denote the binary multiple.

In 1998, the International Electrotechnical Commission (IEC) proposed binary prefixes, introducing “megabyte” for 1,000,000 bytes and “mebibyte” for 1,048,576 bytes. These standards were later adopted by various organizations, including the IEEE, EU, ISO, and NIST. However, despite these standardized definitions, the term “megabyte” is still widely used with different meanings.

In the base 10 convention, 1 MB equals 1,000,000 bytes, adhering to the rules of the International System of Units (SI) and the IEC. This definition is commonly used in computer networking and storage media contexts like hard drives, flash-based storage, and DVDs. It aligns with other uses of SI prefixes in computing, such as CPU clock speeds and performance measures.

On the other hand, in the base 2 convention, 1 MB equals 1,048,576 bytes, particularly in the context of computer memory like RAM. This definition is synonymous with the unambiguous binary unit “mebibyte.” According to this convention, 1 GB is equal to 1,024 MB (1,024^3 bytes), where “GB” stands for gigabyte.

There is also a mixed convention where 1 MB is considered to be 1,024,000 bytes (1,000 × 1,024 bytes). This definition is used to describe the formatted capacity of 1.44 MB 3.5-inch HD floppy disks, even though their actual capacity is 1,474,560 bytes.

In summary, the term “megabyte” can have different meanings depending on the context and the convention used: either 1,000,000 bytes (base 10) or 1,048,576 bytes (base 2).