COP 1000c Lab Assignment 7

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GaddisPythonChapter1IntrotoComputersandProgramming.ppt

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C H A P T E R 1

Introduction to Computers and Programming

Topics

Introduction
Hardware and Software
How Computers Store Data
How a Program Works
Using Python

Introduction

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

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

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

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

Secondary storage: can hold data for long periods of time

Programs normally stored here and loaded to main memory when needed

Types of secondary memory

Disk drive: magnetically encodes data onto a spinning circular disk

Solid state drive: faster than disk drive, no moving parts, stores data in solid state memory

Flash memory: portable, no physical disk

Optical devices: data encoded optically

Input Devices

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

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

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 (cont’d.)

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

Software development tools: used to create, modify, and test software programs

How Computers Store Data

All data in a computer is stored in sequences of 0s and 1s
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 Numbers

Bit represents two values, 0 and 1
Computers use binary numbering system

Position of digit j is assigned the value 2j-1

To determine value of binary number sum position values of the 1s

Byte size limits are 0 and 255

0 = all bits off; 255 = all bits on

To store larger number, use several bytes

Storing Characters

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

Advanced Number Storage

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

Negative numbers encoded using two’s complement

Real numbers encoded using floating-point notation

Other Types of Data

Digital: describes any device that stores data as binary numbers
Digital images are composed of pixels

To store images, each pixel is converted to a binary number representing the pixel’s color

Digital music is composed of sections called samples

To store music, each sample is converted to a binary number

How a Program Works

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.)

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

From Machine Language to Assembly Language

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

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

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
Statement: individual instruction used in high-level language

Compilers and Interpreters

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

Compilers and Interpreters (cont’d.)

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: statements written by programmer

Syntax error: prevents code from being translated

Compilers and Interpreters (cont’d.)

Figure 1-19 Executing a high-level program with an interpreter

Using Python

Python must be installed and configured prior to use

One of the items installed is the Python interpreter

Python interpreter can be used in two modes:

Interactive mode: enter statements on keyboard

Script mode: save statements in Python script

Interactive Mode

When you start Python in interactive mode, you will see a prompt

Indicates the interpreter is waiting for a Python statement to be typed

Prompt reappears after previous statement is executed

Error message displayed If you incorrectly type a statement

Good way to learn new parts of Python

Writing Python Programs and Running Them in Script Mode

Statements entered in interactive mode are not saved as a program
To have a program use script mode

Save a set of Python statements in a file

The filename should have the .py extension

To run the file, or script, type

python filename

at the operating system command line

The IDLE Programming Environment

IDLE (Integrated Development Program): single program that provides tools to write, execute and test a program

Automatically installed when Python language is installed

Runs in interactive mode

Has built-in text editor with features designed to help write Python programs

Summary

This chapter covered:

Main hardware components of the computer

Types of software

How data is stored in a computer

Basic CPU operations and machine language

Fetch-decode-execute cycle

Complex languages and their translation to machine code

Installing Python and the Python interpreter modes