Page 150 - Using MIS

118 Chapter 4 Hardware, Software, and Mobile Systems

1 1 0 1 1 1 0 1
A. Light switches representing 1101 B. Direction of magnetism representing 1101

Figure 4-3
Bits Are Easy to Represent 1 1 0 1
Physically C. Reflection/no reflection representing 1101

surface of the disk so that they will reflect light. In a given spot, a reflection means a one; no
reflection means a zero.

Computer Data Sizes

All forms of computer data are represented by bits. The data can be numbers, characters, cur-
rency amounts, photos, recordings, or whatever. All are simply a string of bits. For reasons that
interest many but are irrelevant for future managers, bits are grouped into 8-bit chunks called
bytes. For character data, such as the letters in a person’s name, one character will fit into one
byte. Thus, when you read a specification that a computing device has 100 million bytes of
memory, you know that the device can hold up to 100 million characters.
Bytes are used to measure sizes of noncharacter data as well. Someone might say, for
example, that a given picture is 100,000 bytes in size. This statement means the length of the
bit string that represents the picture is 100,000 bytes or 800,000 bits (because there are 8 bits
per byte).
The specifications for the size of main memory, disk, and other computer devices are
expressed in bytes. Figure 4-4 shows the set of abbreviations that are used to represent data
storage capacity. A kilobyte, abbreviated K, is a collection of 1,024 bytes. A megabyte, or MB,
is 1,024 kilobytes. A gigabyte, or GB, is 1,024 megabytes; a terabyte, or TB, is 1,024 gigabytes;
a petabyte, or PB, is 1,024 terabytes; an exabyte, or EB, is 1,024 petabytes; and a zettabyte, or
ZB, is 1,024 exabytes. Sometimes you will see these definitions simplified as 1K equals 1,000
bytes and 1MB equals 1,000K, and so on. Such simplifications are incorrect, but they do ease
the math.

Term Definition Abbreviation
Byte Number of bits to represent one character
Kilobyte 1,024 bytes K

Megabyte 1,024 K 1,048,576 bytes MB
Gigabyte 1,024 MB 1,073,741,824 bytes GB
Terabyte 1,024 GB 1,099,511,627,776 bytes TB
Petabyte 1,024 TB 1,125,899,906,842,624 bytes PB

Figure 4-4 Exabyte 1,024 PB 1,152,921,504,606,846,976 bytes EB
Important Storage-Capacity Zettabyte 1,024 EB = 1,180,591,620,717,411,303,424 bytes ZB
Terminology