Unit 1.1 Introduction to python programming

Int. to Programming
(PYTHON)
Copyright © 2018 Pearson Education,
Ltd.

C H A P T E R
1
Introduction
to
Computers
and
Programmin
g
Ltd.

Topics
Ltd.
• Introduction
• Hardware and Software
• How Computers Store Data
• How a Program Works
• Using Python

Introduction
Ltd.
• Computers can be programmed
• Designed to do any job that a program tells
them to
• Program: set of instructions that a
computer follows to perform a task
• Commonly referred to as Software
• Programmer: person who can design,
create, and test computer programs
• Also known as software developer

Hardware and Software
Ltd.
• Hardware: The physical devices that
make up a computer
• Computer is a system composed of
several components that all work together
• Typical major components:
• Central processing unit
• Main memory
• Secondary storage devices
• Input and output devices

The CPU
Ltd.
• Central processing unit (CPU): the part
of the computer that actually runs
programs
• Most important component
• Without it, cannot run software
• Used to be a huge device
• Microprocessors: CPUs located on
small chips

Main Memory
Ltd.
• Main memory: where computer stores a
program while program is running, and
data used by the program
• Known as Random Access Memory or
RAM
• CPU is able to quickly access data in RAM
• Volatile memory used for temporary
storage while program is running
• Contents are erased when computer is off

Secondary Storage Devices
Ltd.
• Secondary storage: can hold data for long
periods of time
• Programs normally stored here and loaded
to main memory when needed
• E.g. Hard disk

Input Devices
Ltd.
• Input: data the computer collects from
people and other devices
• Input device: component that collects
the data
• Examples: keyboard, mouse,
touchscreen, scanner, camera
• Disk drives can be considered input devices
because they load programs into the main
memory

Output Devices
Ltd.
• Output: data produced by the computer
for other people or devices
• Can be text, image, audio, or bit stream
• Output device: formats and presents
output
• Examples: video display, printer
• Disk drives and USB drives can be
considered output devices because data is
sent to them to be saved

Software
Ltd.
• Everything the computer does is
controlled by software
• General categories:
• Application software
• System software
• Application software: programs that
make computer useful for every day
tasks
• Examples: word processing, email,
games, and Web browsers

Software
Ltd.
• System software: programs that control
and manage basic operations of a
computer
• Operating system: controls operations
of hardware components
• Utility Program: performs specific task to
enhance computer operation or safeguard
data
• E.g Data backup programs

How Computers Store Data
Ltd.
• A computer’s memory is divided into
tiny storage locations known as bytes.
• Byte: just enough memory to store
letter or small number
• Divided into eight bits
• Bit: electrical component that can hold
positive or negative charge, like on/off
switch
• The on/off pattern of bits in a byte
represents data stored in the byte

Storing Characters
Ltd.
• Data stored in computer must be stored
as binary number
• Characters are converted to numeric
code, numeric code stored in memory
• Most important coding scheme is ASCII
• ASCII is limited: defines codes for only
128 characters
• Unicode coding scheme becoming standard
• Compatible with ASCII
• Can represent characters for other languages

Ltd.
• To store negative numbers and real
numbers, computers use binary
numbering and encoding schemes

How a Program Works
Ltd.
• CPU designed to perform simple
operations on pieces of data
• Examples: reading data, adding,
subtracting, multiplying, and dividing
numbers
• Understands instructions written in machine
language and included in its instruction set
• Each brand of CPU has its own instruction set
• To carry out meaningful calculation,
CPU must perform many operations

How a Program Works
(cont’d.)
Ltd.
• Program must be copied from
secondary memory to RAM each time
CPU executes it
• CPU executes program in cycle:
• Fetch: read the next instruction from
memory into CPU
• Decode: CPU decodes fetched instruction
to determine which operation to perform
• Execute: perform the operation

How a Program Works
(cont’d.)
Figure 1-16 The fetch-decode-execute cycle
Ltd.

From Machine Language to
Assembly Language
Ltd.
• Impractical for people to write in
machine language
• Assembly language: uses short words
(mnemonics) for instructions instead of
binary numbers
• Easier for programmers to work with
• Assembler: translates assembly
language to machine language for
execution by CPU

High-Level Languages
Ltd.
• Low-level language: close in nature to
machine language
• Example: assembly language
• High-Level language: allows simple
creation of powerful and complex
programs
• No need to know how CPU works or
write large number of instructions
• More intuitive to understand

Key Words, Operators, and
Syntax: an Overview
Ltd.
• Key words: predefined words used to
write program in high-level language
• Each key word has specific meaning
• Operators: perform operations on data
• Example: math operators to perform
arithmetic
• Syntax: set of rules to be followed when
writing program

Compilers and Interpreters
Ltd.
• Programs written in high-level
languages must be translated into
machine language to be executed
• Compiler: translates high-level
language program into separate
machine language program
• Machine language program can be executed
at any time

(cont’d.)
Ltd.
• Interpreter: translates and executes
instructions in high-level language
program
• Used by Python language
• Interprets one instruction at a time
• No separate machine language program
• Source code (or code): statements
written by programmer
• Syntax error: prevents code from
being translated

(cont’d.)
Figure 1-19 Executing a high-level program with an interpreter
Ltd.

Unit 1.1 Introduction to python programming

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