**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".

An expression to calculate how many different numbers can be represented by an 8-bit binary number:

2 x 2 x 2 x 2 x 2 x 2 x 2 x 2

or 2^{8}

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 |

Bytes in a terabyte.....

1024⁴ = 1024×1024×1024×1024 = 1099511627776

**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.

Data | Storage |
---|---|

One extended-ASCII character in a text file (eg 'A') | 1 byte |

The word 'Monday' in a document | 6 bytes |

A plain-text email | 2 KB |

64 pixel x 64 pixel GIF | 12 KB |

Hi-res 2000 x 2000 pixel RAW photo | 11.4 MB |

Three minute MP3 audio file | 3 MB |

One minute uncompressed WAV audio file | 15 MB |

One hour film compressed as MPEG4 | 4 GB |

**Task:** Create a powerpoint including revision information on bits & bytes. Include expressions to show how many bits are in .......

- A byte.
- A nibble.
- For the following write expressions to show both how many
**bits**and**bytes**are in each unit. Make sure you are clear on the difference! - A kilobyte.
- A gigabyte.
- A terabyte.
- For all the byte classifications listed in the text above (up to Yottabyte) Create images to represent their size and capacity (i.e.1 PB = 100 dvd's). This will help you to revise as you will have a viasual image to remind you of the storage capacity.

**Next Task: Past the past paper questions below into your notes then use the internet to research model answers.**

**Next:** Create a python program to calculate bits and bytes in kilobytes and megabytes etc.

**EXT: **See if you can create a python program to create a binary clock.