Page 155 -

Chapter 4 Hardware, Software, and Mobile Systems
154
zero and a closed switch represents one. Or the orientation of a magnetic field can represent a bit:
magnetism in one direction represents a zero; magnetism in the opposite direction represents a
one. Or, for optical media, small pits are burned onto the 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, currency
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 KB, is a collection of 1,024 bytes. A megabyte, or MB, is 1,024 kilo-
bytes. 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 1KB equals 1,000 bytes and 1MB
equals 1,000K, and so on. Such simplifications are incorrect, but they do ease the math.
To put these sizes in perspective consider that, as of 2014, Walmart stores about 2.5 PB worth
2
1
of customer data. Facebook processes about 600 TB each day, in a 300PB data warehouse. The
3
super-secret NSA data center in Utah is estimated to hold about 12 EB of data. And Cisco estimates
that annual global Internet traffic volume will exceed 1.6 ZB by the end of 2018. 4
Specifying Hardware with Computer Data Sizes

Computer disk capacities are specified according to the amount of data they can contain. Thus, a
500GB disk can contain up to 500GB of data and programs. There is some overhead, so it is not
quite 500GB, but it’s close enough.
You can purchase computers with CPUs of different speeds. CPU speed is expressed in cycles
called hertz. In 2015, a slow personal computer had a speed of 3.0 Gigahertz. A fast personal com-
puter had a speed of 3.5+ Gigahertz, with dual processors. As predicted by Moore’s Law, CPU speeds
continually increase.
An employee who does only simple tasks such as word processing does not need a fast CPU; a 2.0
Gigahertz CPU will be fine. However, an employee who processes large, complicated spreadsheets or

6GTO &GHKPKVKQP #DDTGXKCVKQP
$[VG 0WODGT QH DKVU VQ TGRTGUGPV QPG EJCTCEVGT
-KNQD[VG D[VGU -$

/GICD[VG - D[VGU /$
)KICD[VG /$ D[VGU )$
6GTCD[VG )$ D[VGU 6$
2GVCD[VG 6$ D[VGU 2$

Figure 4-4 'ZCD[VG 2$ D[VGU '$
Important Storage-Capacity <GVVCD[VG '$ D[VGU <$
Terminology