Hard drives are measured in bits & bytes -  Ones and Zeros.  In days gone by a 20 gigabyte hard drive was huge.  By today's standards, when a home user can easily install a 1 Terabyte hard drive,  20 GB is very small. 

In round numbers:

• 1 byte would represent a  single character
• Kilobyte (KB) = 1,000 bytes or a short letter
• 1 Megabyte (MB) = 1,000,000 KB or a typical book volume in text format (500 pages × 2000 characters)
• 1 Gigabyte (GB) = 1,000,000,000 MB or the amount of paper needed to fill the bed of a pickup truck, or about 1,000 books
• 1 Terabyte (TB) = 1,000,000,000,000 or over 1,000,000 books
  (about one-tenth the amount of information stored in the Library of Congress)

Example: 

Average Volume 12gb

1. Gigabyte = 1,073,741,824 bytes

• Subtotal  = 12,884,901,888 bytes
• Pages size = 3000 bytes 
• Pages = 4,294,967 
• Ream of paper = 500 pages 
• Reams = 8,590 Reams 
• Ream height = 2” 
• Total height  = 17,180” 
• Height in feet = 1431’ 8’ 
• Height of Sears Tower (Chicago) = 1450'