Page 5 - Computer Programming

TEACHING TIPS
Q Compare and contrast computer
storage capacity. Think of each
capacity as the following: a byte as a
single character, a kilobyte as a short
paragraph, a megabyte as a short
novel, or a high-resolution photo-
graph, a gigabyte as 7 minutes of an
HD video, and a terabyte as 50,000
trees made into paper and printed.
Have students draw pictures in their
notebook to help recall a computer’s
storage capacity.
Q Model the visual representation
of memory locations. Use an egg
carton with plastic Easter eggs to
demonstrate data in addressed
memory locations.
4 CHAPTER 1 Q Computer Programming and the Workplace
4 Chapter 1 Computer Programming and the Workplace
Bits and Bytes
Before we discuss memory, let’s look at how information (data and programs) are
stored in a computer.
A computer is really nothing more than a series of switches. Each switch exists
in two states: on or off. Storing information in a computer is simply a matter of
setting a sequence of switches on or off. If the switch is on, its value is 1. If the
switch is off, its value is 0. These 0s and 1s are interpreted as digits in the binary
bits number system and are called bits (binary digits).
byte The minimum storage unit in a computer is a byte. A byte is composed of eight
bits. A small number such as 3 can be stored as a single byte. To store a number
that cannot fit into a single byte, the computer uses several bytes.
Data of various kinds, such as numbers and characters, are encoded as a series
of bytes. As a programmer, you don’t need to worry about the encoding and
decoding of data, which the computer system performs automatically, based on
encoding scheme the encoding scheme. An encoding scheme is a set of rules that govern how a com-
puter translates characters, numbers, and symbols into data the computer can
actually work with. Most schemes translate each character into a predetermined
string of bits. In the popular ASCII encoding scheme, for example, the character
C is represented as 01000011 in one byte.
A computer’s storage capacity is measured in bytes and multiples of the byte,
as follows:
kilobyte (KB) Q A kilobyte (KB) is about 1,000 bytes.
megabyte (MB) Q A megabyte (MB) is about 1 million bytes.
gigabyte (GB) Q A gigabyte (GB) is about 1 billion bytes.
terabyte (TB) Q A terabyte (TB) is about 1 trillion bytes.
A typical one-page word document might take 20 KB. Therefore, 1 MB can
store 50 pages of documents and 1 GB can store 50,000 pages of documents. A
typical two-hour high- resolution movie might take 8 GB, so it would require 160
GB to store 20 movies.
Memory
memory A computer’s memory consists of an ordered sequence of bytes for storing pro-
grams as well as data that the program is working with. You can think of memory
as the computer’s work area for executing a program. A program and its data must
be moved into the computer’s memory before they can be executed by the CPU.
unique address Every byte in the memory has a unique address, as shown in Figure 1.2. The
address is used to locate the byte for storing and retrieving the data. Since the
bytes in the memory can be accessed in any order, the memory is also referred to
RAM as random-access memory (RAM).
Generally speaking, the more RAM a computer has, the faster it can operate,
but there are limits to this simple rule of thumb.
A memory byte is never empty, but its initial content may be meaningless to
your program. The current content of a memory byte is lost whenever new infor-
mation is placed in it.