COMP 14Introduction to Programming
Miguel A. Otaduy
May 12, 2004
…from Last Time
• Homework 1 due Tomorrow– Fill in form with personal info– Getting started with jGRASP– Compile and Run test programs
– Any problems?
– Disable test for new versions
Today (ch. 1)
• Parts of the computer– hardware vs. software– CPU and memory
• Binary numbers
• What is an algorithm?
Reading Check-Up
1. - computer components including the CPU, main memory, I/O devices, and secondary storage
2. - the brain of the computer, containing the CU, PC, IR, ALU, and ACC
3. - computer instructions to solve a problem
4. The digits 0 and 1 are calledor the shortened term
hardware
CPU
program
binary digits
bits
Hardware vs. Software
A computer is made up of hardware and software
Hardware Software• CPU
- ex: 1 GHz Pentium III• input/output
- keyboard- monitor- network card
• main memory- ex: 256 MB RAM
• secondary memory- ex: 20 GB hard drive
• operating systems- Windows XP- Mac OS X
• applications- games- Microsoft Word- Internet Explorer
Hardware Organization
motherboard
CPU
memory
hard drive
Central Processing UnitCPU• Control Unit (CU)
– "the brain" of the CPU
• Program Counter (PC)– points to the next instruction to be executed
• Instruction Register (IR)– holds the currently executing instruction
• Arithmetic Logic Unit (ALU)– carries out all arithmetic and logical ops
• Accumulator (ACC)– holds the results of the operations
performed by the ALU
Main Memory
• Ordered sequence of cells
• AKA Random Access Memory (RAM)
• Directly connected to the CPU
• All programs must be brought into main memory before execution
• When power is turned off, everything in main memory is lost
Main MemoryWith 100 Cells
Each memory cell has a numeric address, which uniquely identifies it
CPU and Main Memory
Chip that executesprogram instructions(processor)
Primary storage areafor programs and datathat are in active use(RAM)
All programs must be brought into main memory before execution
Secondary Storage
• Provides permanent storage for information• Retains information even when power is off• Examples of secondary storage:
– Hard Disks– Floppy Disks– ZIP Disks– CD-ROMs– Tapes
Secondary Storage
Secondary memorydevices providelong-term storage
Information is movedbetween main memoryand secondary memoryas needed
Input Devices
• Definition: devices that feed data and computer programs into computers
• Examples:– Keyboard– Mouse– Secondary Storage
Output Devices
• Definition: devices that the computer uses to display results
• Examples:– Printer– Monitor– Secondary Storage
Input/Output Devices
I/O devices facilitateuser interaction
Hardware Components
Opening MS Word• Use the mouse to
select MS Word• The CPU requests
the MS Word application
• MS Word is loaded from the hard drive to main memory
• The CPU reads instructions from main memory and executes them one at a time
• MS Word is displayed on your monitor
Questions
1. - points to the next instruction to be executed
2. - a unique location in memory
3. - stores information permanently
4. Instructions executed by the CPU must be first loaded to
program counter (PC)
address
secondary storage
main memory
Software Categories
• Operating System– controls all machine activities– provides the user interface to the computer– first program to load when a computer is
turned on– manages computer resources, such as the
CPU, memory, and hard drive– examples: Windows XP, Linux, Mac OS X
• Application– generic term for any other kind of software– examples: word processors, missile control
systems, games
Operating System (OS)
• OS monitors overall activity of the computer and provides services
• Written using programming language
• Example services:– memory management– input/output– storage management
Application Programs
• Written using programming languages
• Perform a specific task• Run by the OS• Example programs:
– Word Processors– Spreadsheets– Games
Questions
Classify the following pieces of software as operating system or application:
1. Microsoft Windows 20002. Microsoft PowerPoint3. Linux4. Your COMP 14 programs
OS
OS
app
app
It’s All About Data
• Software is data– numbers, characters– instructions, programs
• Hardware stores and processes data– read, write– add, subtract, multiply, divide
Analog vs. Digital
• Analog– continuous wave forms– ex: sound, music on an audio tape
• Digital– the information is broken down into pieces,
and each piece is represented separately– represented as series of 0 and 1
• 0 - low voltage• 1 - high voltage
– can be copied exactly– ex: music on a compact disc
H i , H e a t h e r .
72 105 44 32 72 101 97 116 104 101 114 46
Representing Text Digitally• All information in a computer is
digitized, broken down and represented as numbers.
Corresponding upper and lower case Corresponding upper and lower case letters are separate characters.letters are separate characters.
Language of a Computer• Machine language: the most basic
language of a computer
• A sequence of 0s and 1s– binary digit, or bit– sequence of 8 bits is called a byte
• Every computer directly understands its own machine language– why can't Windows programs run on Apple
computers?
1 bit01
2 bits
00011011
3 bits
000001010011100101110111
4 bits
00000001001000110100010101100111
10001001101010111100110111101111
Each additional bit doubles the number of possible permutations
Bit Permutations
21 = 2 items
22 = 4 items
23 = 8 items
24 = 16 items
25 = 32 items
1 bit ?
2 bits ?
3 bits ?
4 bits ?
5 bits ?
How manyitems can be
represented by
Bit Permutations
• Each permutation can represent a particular item
• There are 2N permutations of N bits– N bits are needed to represent 2N
unique items
Binary Numbers
• N bits to represent 2N values• N bits represent values 0 to 2N-1• Example: 5 bits
– 32 unique values (0-31)– 00000 = 0– 11111 = 31
24 23 22 21 20
16 + 8 + 4 + 2 + 1
Decimal to Binary
114 1110010
Place Digit Value26 1 64
25 1 3224 1 1623 0 022 0 021 1 220 0 0
QuestionsBinary Numbers
• What’s the maximum value a 6-bit number can represent?
• What’s the decimal representation of 111010?
• What’s the binary representation of 35?
63
58 = 32+16+8+2
100011
KB 210 = 1024
MB 220 (over 1 million)
GB 230 (over 1 billion)
TB 240 (over 1 trillion)
Unit Symbol Number of Bytes
kilobyte
megabyte
gigabyte
terabyte
Storage Capacity
• Every memory device has a storage capacity, indicating the number of bytes (8 bits) it can hold
• Various units:
Programming LanguagesEvolution• Early computers programmed in
machine language (only 0s and 1s)
• Assembly languages were developed to make programmer’s job easier
• Assembler: translates assembly language instructions into machine language
Assembly and Machine Language
Programming LanguagesEvolution
• High-level languages make programming easier
• Closer to spoken languages• Examples:
– Basic – FORTRAN– COBOL– C/C++– Java
From Java to Machine Language• Computers understand only 0 and 1 (machine
language)• Compiler translates source code into machine
code
• Java compiler translates source code (file ending in .java) into bytecode (file ending in .class)– bytecode is portable (not machine-specific)
• Java interpreter reads and executes bytecode– different Java interpreters for different types of CPUs
and operating systems (OS)• Intel/Windows, Motorola/Mac OS X, Intel/Linux
Problem Solving• The purpose of writing a program is to solve a
problem
• The general steps in problem solving are:– understand the problem– dissect the problem into manageable pieces– design a solution– consider alternatives to the solution and refine it– implement the solution– test the solution and fix any problems that exist
Algorithm
• Sequence of instructions used to carry out a task or solve a problem
• May be written in either English or pseudocode– outline of a program that could be
translated into actual code
• May need refinement as you work
Always write out your algorithm before you begin programming
Problem-Analysis-Coding-Execution
most important stepwithoutcomputer
withcomputer
Algorithm Design Example
Problem: Convert change in cents to number of half-dollars, quarters, dimes, nickels, and pennies to be returned.
Example: – given 646 cents– number of half-dollars: divide 646 by 50
• quotient is 12 (number of half-dollars)• remainder is 46 (change left over)
– number of quarters: divide 46 by 25• quotient is 1 (number of quarters)• remainder is 21 (change left over)
– number of dimes, nickels, pennies– result: 12 half-dollars, 1 quarter, 2 dimes, 0
nickels, 1 penny
Resulting Algorithm
1. Get the change in cents2. Find the number of half-dollars3. Calculate the remaining change4. Find the number of quarters5. Calculate the remaining change6. Find the number of dimes7. Calculate the remaining change8. Find the number of nickels9. Calculate the remaining change10.The remaining change is the number of
pennies.
Exercise
• Execution of c=2*a+b in a computer
To do
• Read ch. 2• Exercises 10 & 11 in ch. 1
(algorithm design)
What’s Ahead...
• Java Basics
• Homework 1 due tomorrow• Homework 2 assigned tomorrow
• Quiz Friday: computers and Java basics