28-February-2007CMP 131 Introduction to Computers and Programming1 CMP 131 Introduction to Computer...

28-February-2007 CMP 131 Introduction to Computers and Programming 1

CMP 131Introduction to Computer

Programming

Violetta Cavalli-SforzaWeek 1, Lecture 2


Outline of Topics• Review briefly last class

• More details about hardware

• Software/Hardware interface– Data and program representation– Machine arithmetic


Last Class

• Course Description

• Logistics

• Assessments (Grading)

• Homework– First assignment will come out Monday


Last Class (2)

• Computers: What’s in them?– Hardware– Software

• Hardware devices

• Computers through time

• Hardware trends

• Hardware/software trends


Why Take This Course?

• Be more familiar with PCs • Have a basic understanding of programming and the

programming process• Develop critical thinking & problem solving capabilities• Learn other programming languages faster & easier


Why Pascal?

• One of the first structured programming languages

• It influenced the design of its successors– Modula 2, Oberon (by N.Wirth)– Modula2+, Modula3 (DEC, Olivetti) – Java– Not C or C++


Today’s Lecture

• Review of computers and hardware– Some more information

• More about software• Programming languages

– Low and high-level languages– Viewing programming through different

languages

• Introduction to the Pascal IDE environment


Computer Systems• Computers

– Devices for performing computations at high speeds with great accuracy

– A machine that can be programmed to manipulate symbols. Can perform complex & repetitive procedures quickly, precisely and reliably. Can quickly store and retrieve large amounts of data.

• Program– A set of instructions for a computer to follow,

written in specific programming language


Computer Systems• Hardware (HW)

–Actual physical machines (equipment) that make up the computer

• Software (SW) –A collection of programs used by a

computer–A set of instructions provided by the

programmer that the computer follows. –Program instructions have to be stored

in main memory before they can be executed.


Computer Systems• Computer Categories:

– Microcomputers (Personal computers / PCs)• Used by a single person

– Workstations:• Largest microcomputers

– Minicomputers:• Can be used by many people simultaneously by using

several terminals connected to the same CPU– Main frame computers:

• Faster & larger than minicomputers– Super computers:

• Most powerful mainframe computers

• Of which category is you computer at home??


Hardware (HW): Organization• Computer HW usually consists of:

– CPU – Main memory (RAM & ROM)– I/O Devices– Secondary Memory

• CPU & main memory are the heart of the computer • Usually the CPU, main memory and secondary memory are

housed in a single cabinet

CPU

Main Memory

I/O Devices

Secondary Memory


Hardware (HW): Central Processing Unit (CPU)

• Executes programs• Performs calculations

– Arithmetic• Add, subtract, divide, multiply, … etc.

– Logical• Compare, test for true/false

• Controls & coordinates the other parts of the computer.


Hardware (HW): Memory• Main (Primary) Memory:

– Ordered sequence and specific number of memory locations (Bytes, words) that have unique addresses indicating their relative positions

– Fast, expensive, short term memory – Holds intermediate results and serves as “scratch

paper”– Needed to carry out program instructions– Types:

• RAM: Random Access Memory (vs. Sequential Access Memory)

• Volatile (i.e. contents disappear when the computer is switched off)

• Writable (except where forbidden by the software)• ROM: Read Only Memory

• Non-volatile• Also usually random access


Hardware (HW): Memory

• Secondary (auxiliary) memory– Used for keeping a permanent records of

information– Holds programs and data between jobs– Keeps data or program files for later use– Slower, cheaper, long-term memory– Common forms

• Diskettes, magnetic tapes, hard disk, CD-ROM’s, DVD

– Some types are removable


Hardware (HW)

• I/O (Input/Output) devices– Allow the user to communicate with the

computer.– A single computer could be connected to

more than one input or output device.– Examples:

• Input: Keyboard, mouse, scanner, voice• Output: Screen, printer, voice


Hardware/Software Architectures

• Mainframe Era– 1940’s-70’s: mainframe computer,

minicomputers– Environments:

• Batch environments, batch processing– Files are basis for I/O: fixed formats, minimal device I/O– Error recovery– Lack of timing constraints

• Interactive environments– Terminal and file I/O:– Interactive error handling– Faster performance


• Personal Computers Era– 1978: the Apple II ran BASIC

• Educational use

– 1981: IBM released the first PC – 1984: Macintosh– Window environments:

• OO models are ideal (Smalltalk)• Must interact with many I/O devices (file I/O is less

important)

– Embedded systems• Error handling• Real-time response• Distributed systems with concurrently running tasks


• Networking Era:– LANs (Local Area Networks):

client-server model• Airline reservations, banking

– Internet • 70’s: ARPANET: telnet, FTP, SMTP protocols• late 80’s: HTML and HTTP added

– Issues and Effects:• Static web pages with URLs for access

URL = Uniform Resource Locator• Dynamic web pages for e-commerce (Perl, JAVA, etc.)• Security• Performance (multiple clients)

– Offloading work to client


Hardware/Software Concepts

• Computers manipulate instructions and data– Represented in similar ways– Used in different ways– Representation is binary (digital hardware is binary)

• Numbers vs. symbols– Computers represent everything as numbers– But numbers can represent symbols– Can perform “symbolic” computation

• Beginning of Artificial Intelligence


HW/SW Concepts: Data What is it?

Numbers, characters, images, or other method of recording Can be assessed by a human or (especially) input into a computer,

stored and processed there, or transmitted on some digital channel. Nearly always represent data in binary. Has no meaning on its own. When interpreted by data processing system it takes on meaning and

becomes information.

Storage– Setting of individual bits to specific values, destroying its previous

contents

Retrieval– Copying the contents of a particular memory cell to another storage

area.– Original data remains unchanged


HW/SW Concepts: Representation

• Digit / Bit– Smallest unit of information/storage, sufficient

to hold one bit – Can take one of two values

(true/false, 1/0, or yes/no)– Corresponds to an input/output being on or off

• Byte– Smallest addressable unit of storage– Usually 8 bits– Typically holds one character– Can represent 256 different values


HW/SW Concepts: Representation

• Word– Fundamental unit of storage in a computer– Word size is one of its chief distinguishing

characteristics of a computer– Typical size in modern computers: 32 bits (4

bytes) or 64 bits (8 bytes)– An instruction is usually one or more words

long– A word can be used to hold a whole number

of characters


Decimal Number System

• A base 10 system

• Each digit position can hold 10 values (0-9)Ex. 1234 = 4*1 + 3 * 10 + 2*100 + 1*1000= 4*100 + 3 * 101 + 2*102 + 1*103


Binary Number System

• A base 2 system• Each digit position can hold 2 values (0-1)

Ex. 1011• Decimal conversion

– Equals: 1*20 + 1*21 + 0*22 + 1*23

– Equals: 1 + 2 + 0 + 8 = 11• Maximum number of values in 4 bits: 16

– 0 to 15• Maximum number of values in 8 bits: 256

– 0 to 255 [or -128 to 127]– This is how much you can store in a byte


Binary Numbers0000 0

0001 1

0010 2

0011 3

0100 4

0101 5

0110 6

0111 7

1000 8

1001 9

1010 10

1011 11

1100 12

1101 13

1110 14

1111 15


Binary Addition

1010 +0101 =---------1111

1010 +0011 =---------1101

1010 +0111 =---------0001

10 + 5 =------15

10 + 3 =------13

10 + 7 =------17 => 1 OVERFLOW!!!


Other Number Systems

• Hexadecimal: base 16– Each digit can hold 16 values (0-9,A-F)– Ex: A02F– Decimal conversion?– Note: 1 hex digit = 4 binary digits

• Octal: base 8– Each digit can hold 8 values (0 to 7)– Ex: 127 – Decimal conversion?


Logical Operations

• AND:– 1 AND 1 = 1– Everything else = 0

• OR– 0 AND 0 = 0– Everything else = 1

• XOR (Exclusive OR)– 0 AND 1 = 1– 0 AND 0 = 0, 1 AND 1 = 0

28-February-2007CMP 131 Introduction to Computers and Programming1 CMP 131 Introduction to Computer...

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