Computer Science Theory & Introduction

Week 1 Lecture Material – F'13 RevisionDoug Hogan

Penn State University

CMPSC 201 – C++ Programming for EngineersCMPSC 202 - FORTRAN Programming for Engineers

Hardware vs. SoftwareHardware essentially, things you can touch input, output, storage devices memory

Software essentially, what the computer knows data, 0s and 1s programs (this is a software course)

Categories of Memory

Read-only memory (ROM)can only read data

Random-access memory (RAM)can read and write informationprimary storage - computer’s main

memoryvolatile

Sequential Access vs. Random Access MemorySequential Access:must access each location in memory in order

Random Access: can access memory locations using addresses, in any order

Speed implications?

Track 1

Track 2

Measuring Memory

base unit: 1 bit = binary digit, 0 or 18 bits = 1 byte (B)1000 bytes ≈ 1 kilobyte (KB)1000 KB ≈ 1,000,000 B ≈ 1 megabyte (MB)1000 MB ≈ 1,000,000,000 B ≈ 1 gigabyte (GB)1000 GB ≈ 1,000,000,000,000 B ≈ 1 terabyte (TB)

Storage Device Capacities

Floppy disk (the old 3.5” ones) 1.44 MB

Compact disc (CD) 650-700 MB

Digital Versatile/Video Disc (DVD) 4.7 GB

Hard disks, flash drives typically sizes in GB

Software Overview

System softwareControls basic operations of computerThe operating system

manages memory, files, application software

File management tasks – deleting, etc.

Software Overview

Application softwareNot essential to system runningEnables you to perform specific tasksEx:

Office softwareWeb browsersMedia playersGames

Algorithms and Languages

An algorithm is a set of instructions to solve a problem.Think recipes.Many algorithms may solve the same problem. How do we choose?

We use a programming language to explain our algorithms to computer and write programs.

Programming Paradigms/Models

Imperative Programming: specify steps to solve problem, use methods, methods could get longObject-Oriented Programming (OOP): create objects to model real-world phenomena, send messages to objects, typically shorter methodsEvent-Driven Programming: create methods that respond to events like mouse clicks, key presses, etc. Others: Functional, logic, etc.

Compiled vs. Interpreted Languages

Interpreted Language Requires software

called an interpreter to run the code

Code is checked for errors as it runs (erroneous code: do the best we can…)

Examples: HTML, JavaScript, PHP

Compiled Language Requires software

called a compiler to run the code

Code must be compiled into an executable before running (and thus error-free)

Examples: C, C++, Pascal, Fortran, BASIC

Compiling Process

Source Code

(C++, Fortran, …)

ObjectCode

ExecutableProgram

ObjectCode fromLibraries

compiler linker

ErrorsSyntax Errors Misuse of the language, much like using

incorrect punctuation in English Compiler reports; program won’t run until

they’re resolved

Logic Errors Program doesn’t solve the problem at hand

correctly

Runtime Errors Errors that occur while the program is

running, e.g. problems accessing memory and files, divide by zero

AbstractionPoll: Who can use a CD player? Who can explain how a CD player works? Who can drive a car? Who is an auto mechanic?

Abstraction Principle of ignoring details that allows us to

use complex devices Focus on the WHAT, not the HOW Fundamental to CS Other examples?

Levels of Abstraction

0. Digital Logic1. Microprocessor2. Machine Language3. Operating System4. Assembly Language5. High-Level Language6. Application Software

Binary Numbers

Use two symbols: 0 and 1Base 2Compare with decimal number systemUses symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, 9Base 10

At the lowest level of abstraction, everything in a computer is expressed in binary.

Binary Numbers, ctd.

01

1011

100101110111

Places: Decimal: 1s, 10s, 100s,

etc. Binary, 1s, 2s, 4s, 8s,

etc.

Conversion between decimal and binary is done by multiplying or adding by powers of 2. “There are 10 kinds of people in the world…”

10001001101010111100110111101111

10000

Other Number Systems

Any positive integer could be the base of a number system. (Big topic in number theory.)Others used in computer science:Octal: Base 8Hexadecimal:

Base 16New symbols A, B, C, D, E, F

ASCII

Every character on a computer -- letters, digits, symbols, etc. -- is represented by a numeric code behind the scenes.This system of codes is called ASCII, short for American Standard Code for Information Interchange.We’ll learn more in lab…

# Transistors on a Processor

Processor Date Number of Transistors

4004 1971 2,250

8008 1972 2,500

8080 1974 5,000

8086 1978 29,000

286 1982 120,000

386 1985 275,000

486 DX 1989 1,180,000

Pentium 1993 3,100,000

Pentium II 1997 7,500,000

Pentium III 1999 24,000,000

Pentium 4 2000 42,000,000

Data forIntel processors:

Data from Section 4.1 of :

Yates, Daniel S., and David S. Moore and Daren S. Starnes. The Practice of Statistics. 2nd Ed. New York: Freeman, 2003.

A Graphical View

Graph from Intel's web site (http://www.intel.com/technology/mooreslaw/index.htm); Retrieved 9/24/2006

Pay attention to the units on the axes…

Moore’s Law

Prediction from Gordon Moore of Intel in 1965.Implication: The speed of processors doubles roughly every 12 to 18 months.Exponential relationship in the data. For the curious: the regression equation from the

data two slides back is

Can this go on forever?

ˆ y 1648.161.393x