As a measure of computer processor storage and real and virtual memory, a megabyte (abbreviated MB) is 2 to the 20th power bytes, or 1,048,576 bytes in decimal notation.

According to the IBM Dictionary of Computing, when used to describe disk storage capacity and transmission rates, a megabyte is 1,000,000 bytes in decimal notation.

According to Eric S. Raymond in The New Hacker's Dictionary, a megabyte is always 1,048,576 bytes on the argument that bytes should naturally be computed in powers of two.

Iomega Corporation uses the decimal megabyte in calling the Zip drive disk a "100MB disk" when it actually holds 100,431,872 bytes. If Iomega used the powers-of-two megabyte, the disk could be said to hold only 95.8 megabytes (if you divide 100,431,872 by 1,048,576).