## 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.