# ARCHIVED: What are bits, bytes, and other units of measure for digital information?

A bit is a binary digit, the smallest increment of data on a computer. A bit can hold only one of two values: 0 or 1, corresponding to the electrical values of off or on, respectively.

Because bits are so small, you rarely work with information one bit at a time. Bits are usually assembled into a group of eight to form a byte. A byte contains enough information to store a single ASCII character, like "h".

A kilobyte (KB) is 1,024 bytes, not one thousand bytes as might be expected, because computers use binary (base two) math, instead of a decimal (base ten) system.

Computer storage and memory is often measured in megabytes (MB) and gigabytes (GB). A medium-sized novel contains about 1 MB of information. 1 MB is 1,024 kilobytes, or 1,048,576 (1024x1024) bytes, not one million bytes.

Similarly, one 1 GB is 1,024 MB, or 1,073,741,824 (1024x1024x1024) bytes. A terabyte (TB) is 1,024 GB; 1 TB is about the same amount of information as all of the books in a large library, or roughly 1,610 CDs worth of data. A petabyte (PB) is 1,024 TB. 1 PB of data, if written on DVDs, would create roughly 223,100 DVDs, i.e., a stack about 878 feet tall, or a stack of CDs a mile high. Indiana University is now building storage systems capable of holding petabytes of data. An exabyte (EB) is 1,024 PB. A zettabyte (ZB) is 1,024 EB. Finally, a yottabyte (YB) is 1,024 ZB.

Many hard drive manufacturers use a decimal number system to define amounts of storage space. As a result, 1 MB is defined as one million bytes, 1 GB is defined as one billion bytes, and so on. Since your computer uses a binary system as mentioned above, you may notice a discrepancy between your hard drive's published capacity and the capacity acknowledged by your computer. For example, a hard drive that is said to contain 10 GB of storage space using a decimal system is actually capable of storing 10,000,000,000 bytes. However, in a binary system, 10 GB is 10,737,418,240 bytes. As a result, instead of acknowledging 10 GB, your computer will acknowledge 9.31 GB. This is not a malfunction but a matter of different definitions.

We count in base 10 by powers of 10:

10^{1}= 10 10^{2}= 10*10 = 100 10^{3}= 10*10*10 = 1,000 10^{6}= 1,000,000

Computers count by base 2:

2^{1}= 2 2^{2}= 2*2 = 4 2^{3}= 2*2*2 = 8 2^{10}= 1,024 2^{20}= 1,048,576

So in computer jargon, the following units are used:

Unit | Equivalent |
---|---|

1 kilobyte (KB) | 1,024 bytes |

1 megabyte (MB) | 1,048,576 bytes |

1 gigabyte (GB) | 1,073,741,824 bytes |

1 terabyte (TB) | 1,099,511,627,776 bytes |

1 petabyte (PB) | 1,125,899,906,842,624 bytes |

**Note: **The names and abbreviations for numbers of
bytes are easily confused with the notations for bits. The
abbreviations for numbers of bits use a lower-case "b" instead of an
upper-case "B". Since one byte is made up of eight bits, this
difference can be significant. For example, if a broadband Internet
connection is advertised with a download speed of
3.0 M**b**ps, its speed is 3.0 mega**bits**
per second, or 0.375 mega**bytes** per second (which
would be abbreviated as 0.375 M**B**ps). Bits and bit rates
(bits over time, as in bits per second [bps]) are most commonly used
to describe connection speeds, so pay particular attention when
comparing Internet connection providers and services.

*This is document* ackw *in the Knowledge Base.*

*Last modified on* 2018-01-18 10:52:24*.*