# How Many CDs Do You Need To Get To The Moon?

Only a decade ago, data storage capacities for a typical home computer were measured in Megabytes. Nowadays a typical hard drive capacity is hundreds of Gigabytes, and the newest models are breaching the Terabyte range. Considering the rate at which we are moving up through our storage nomenclature, how long will it be before our current list of denominations becomes inadequate?

Joseph Pisano has made such a list, which presents the volumes in terms of a stack of Compact Discs. This is an entertaining and informative way of explaining the exponential nature of our measurement system, and clearly illustrates that we won’t have to worry about running out of prefix multipliers for quite some time…

I bought my first PC in 1997 – a Pentium 90 with a hard drive of 512 Megabytes (less storage capacity than a single Compact Disc!). Before that, I owned an Atari ST – boasting a robust 512 Kilobytes of memory. Going back a bit further, we meet the ZX Spectrum and the Commodore Vic 20 (yes, 20k of memory!).

We are probably all familiar with these orders of magnitude – Kilo, Mega, Giga – but to see exactly how the numbers stack up, we need to look at a few of Pisano’s calculations, based on a CD thickness of 1.2 mm or 0.048 inches.

[Kilostack]1,000 CDs = 1.2 m or 48 inches

[Megastack]1,000,000 CDs = 1,200 m or 47,244.1 inches

3,937 feet, ¾ of a mile long

[Gigastack]1,000,000,000 CDs = 745 miles

The distance from NYC to Chicago – less 50 miles

[Terrastack]1,000,000,000,000 CDs = 745,645 miles

Over three times the distance from the Earth to the Moon

[Petastack]Lots of CDs = 8.2 Astronomical Units (AU)

The distance from the Sun, past Jupiter -almost to Saturn

[Exastack]Oh My! CDs = 8021.5 AU

.12 of a Light Year or 706 billion miles!

[Zetastack]You can’t even imagine! CDs = 126.8 Light Years

38.9 Parsecs. A little over a 10th the length or our galaxy

[Yottastack]Fahgetaboutit! CDs = 38,889 Parsecs

All the way across the Milky Way – Plus!

For those of you who prefer your data to be tabular, here is a comparison of the values as expressed in binary and decimal. For values smaller than a unit, you can refer to an expanded version of the table at Techtarget.

Prefix |
Symbol |
Power of Ten |
Power of Two |

(none) | — | 10^{0} |
2^{0} |

deka- | D | 10^{1 *} |
— |

hecto- | h | 10^{2 *} |
— |

kilo- | k or K ^{**} |
10^{3} |
2^{10} |

mega- | M | 10^{6} |
2^{20} |

giga- | G | 10^{9} |
2^{30} |

tera- | T | 10^{12} |
2^{40} |

peta- | P | 10^{15} |
2^{50} |

exa- | E | 10^{18 *} |
2^{60} |

zetta- | Z | 10^{21 *} |
2^{70} |

yotta- | Y | 10^{24 *} |
2^{80} |

* Not generally used to express data speed | |||

** k = 10^{3} and K = 2^{10} |