Copyright Goodheart-Willcox Co., Inc. 12 Introduction to Microsoft Offi ce hard disk drive is the most common example of a magnetic medium. A hard disk drive, or hard drive, is a sealed unit that contains a stack of individual disks, or platters, which are magnetic media that rotate at a very high speed, as shown in Figure 1-10. Solid-state storage media, such as fl ash drives, is based on circuitry rather than magnetic media. Read head Platters Hellen Sergeyeva/Shutterstock.com Figure 1-10. A hard disk drive consists of multiple platters. The unit is enclosed, but the cover has been removed in this photo. Goodheart-Willcox Publisher Figure 1-9. Quantities of bytes and approximate storage capacity. Metric Symbols Number of Bytes* Equivalent Sizes byte 1 One character. kilobyte (KB) 1 thousand bytes One short letter or memo. megabyte (MB) 1 million bytes A typical high-resolution photo is about 2.5MB. The information in 40 paperback books (a stack about three feet high) is about 50MB. gigabyte (GB) 1 billion bytes One hour of a feature film is about 1.5GB. The information in 800 paperback books (a stack about 650 feet high) is about 20GB. terabyte (TB) 1 trillion bytes The information in 800,000 paperback books (a stack about 10 miles high) is about 1TB. Library of Congress archives contain 160TB. petabyte (PB) 1,000 terabytes Seventy-seven million CDs each containing 700MB is 50PB. exabyte (EB) 1,000 petabytes All words ever spoken by human beings are about 5EB. zettabyte (ZB) 1,000 exabytes The information in 174 newspapers received daily by every person on Earth is about 4ZB. *Note: there are actually 1,024 bytes in a kilobyte, so these values are rounded.