The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. Therefore, one megabyte is one million bytes of information. This definition has been incorporated into the International System of Quantities. The gigabyte is a multiple of the unit byte for digital information. Therefore, one gigabyte is bytes. The unit symbol for the gigabyte is GB. However, most people have requested the more common usage, so the non-SI version is used on this site.
A gigabyte is a unit of information or computer storage meaning approximately 1. This is the definition commonly used for computer memory and file sizes. Microsoft uses this definition to display hard drive sizes, as do most other operating systems and programs by default. This means that a GB hard disk drive would appear as " GB".
Most users prefer to convert units using the most common definition, so this site uses the non-SI form. An MP3 audio file of a few minutes or a 10 million pixel image from a digital camera would typically take up few megabytes. The rule of thumb for MP3 audio is that 1 minute of audio takes up about 1 megabyte. Audio and image and video data typically stored in "compressed" form, MP3 being an example. We'll talk about how compression works later.
A data CD disk stores about MB. The audio on a CD is not compressed, which is why it takes so much more space than the MP3. The series of bits are represented as spiral path of tiny pits in the silver material in the disk. Imagine that each pit is interpreted as a 0, and the lack of a pit is a 1 as the spiral sequence is read. Fun fact: the whole spiral on a CD is over 5km long. A flash memory card used in a camera might store 16 GB. How many fit on a 16 GB flash drive? You can buy 4 TB hard drives today, so we are beginning the time when this term comes in to common use.
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