# Number Prefixes

## Yottabytes Are a Lotta Bytes

**By Stephen Beck**

Now that kilo-, mega- and even gigabytes of computer memory look like small beer, and computer clock speeds even in nanoseconds begin to feel pokey, it1s time to learn the next set of exponential prefixes destined to enter the modern vocabulary. Brace yourself for the coming world of computers with yottabyte memories and zeptosecond clock speeds (and Government deficits measured in petabucks).

### Really Big Numbers

PREFIX |
POWERof 10 |
UNITS |
NUMBER |

kilo- | 3 | thousands | 1,000 |

mega- | 6 | millions | 1,000,000 |

giga- | 9 | billions | 1,000,000,000 |

tera- | 12 | trillions | 1,000,000,000,000 |

peta- | 15 | quadrillions | 1,000,000,000,000,000 |

exa- | 18 | quintillions | 1,000,000,000,000,000,000 |

zetta- | 21 | sextillions | 1,000,000,000,000,000,000,000 |

yotta- | 24 | septillions | 1,000,000,000,000,000,000,000,000 |

**How long would it take someone to download a one- yottabyte file using a 28.8 baud modem? 11 trillion years.**

### Really Small Numbers

PREFIX |
POWERof 10 |
UNITS |
NUMBER |

milli- | 3 | one thousandth | .001 |

micro- | 6 | one millionth | .000001 |

nano- | 9 | one billionth | .000000001 |

pico- | 12 | one trillionth | .000000000001 |

femto- | 15 | one quadrillionth | .000000000000001 |

atto- | 18 | one quintillionth | .000000000000000001 |

zepto- | 21 | one sextillionth | .000000000000000000001 |

yocto- | 24 | one septillionth | .000000000000000000000001 |

*Source: National Institute of Standards and Technology *

##### Illustration: Randy Jones for The New York Times

Copyright 1996 The New York Times Company