## Comparing the Size of the Human Genome With a Computer Operating System

The human genome is written in a code consisting of molecules called bases labelled A, G, C, T. There are about 3 billion or\[3 \times 10^9\]

of these letters in a human genome.We can write the human genome in binary code using the following labelling:

A is labelled 00

G is labelled 01

C is labelled 10

T is labelled 11

With this labelling ACTTGC becomes 001011110110 for example.

When written in binary code like this, the genome is twice as long, containing about

\[6 \times 10^9\]

digits. 1 kilobit contains \[1024 \simeq 10^3\]

digits.1 megabit contains

\[1048576=10^6\]

digits.1 gigabyte contains

\[1073741824=10^9\]

digits.The human genome is then about 3 gigabits long. 1 byte equals 8 bits so the genome is about

\[\frac{3 \times 10^9}{8} \simeq 400 \]

megabytes long. As of 204 a typical home computer operating system is 700 megabytes long, about twice as long as the human genome.