Answer
$1000000\text{ MB}=1\text{ TB}$
Work Step by Step
Let us assume each book have 500 page and each page has 2000 characters.
=> total characters in one books = $500\times 2000= 10^{6}$
=> total characters in $10^{6}$ books = $10^{6}$
In ASCII representation, each character will take 1 byte
=> total memory size = $10^6$ bytes = $1$ MB
Total size for $1$ million books:
$1000000\times 1\text{ MB}=1000000\text{ MB}=1\text{ TB}$
