CMP 131 Introduction to Computer Programming Violetta CavalliSforza

CMP 131 Introduction to Computer Programming Violetta Cavalli-Sforza Week 1, Lecture 2 28 -February-2007 CMP 131 Introduction to Computers and Programming 1

Outline of Topics • Review briefly last class • More details about hardware • Software/Hardware interface – Data and program representation – Machine arithmetic 28 -February-2007 CMP 131 Introduction to Computers and Programming 2

Last Class • • Course Description Logistics Assessments (Grading) Homework – First assignment will come out Monday 28 -February-2007 CMP 131 Introduction to Computers and Programming 3

Last Class (2) • Computers: What’s in them? – Hardware – Software • • Hardware devices Computers through time Hardware trends Hardware/software trends 28 -February-2007 CMP 131 Introduction to Computers and Programming 4

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 5

Why Pascal? • One of the first structured programming languages • It influenced the design of its successors – Modula 2, Oberon (by N. Wirth) – Modula 2+, Modula 3 (DEC, Olivetti) – Java – Not C or C++ 28 -February-2007 CMP 131 Introduction to Computers and Programming 6

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 7

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 8

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. 28 -February-2007 CMP 131 Introduction to Computers and Programming 9

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? ? 28 -February-2007 CMP 131 Introduction to Computers and Programming 10

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 I/O Devices CPU Secondary Memory Main Memory 28 -February-2007 CMP 131 Introduction to Computers and Programming 11

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. 28 -February-2007 CMP 131 Introduction to Computers and Programming 12

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 13

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 14

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 15

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 16

• 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 28 -February-2007 CMP 131 Introduction to Computers and Programming 17

• 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 28 -February-2007 CMP 131 Introduction to Computers and Programming 18

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 19

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 20

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 21

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 22

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 23

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 28 -February-2007 CMP 131 Introduction to Computers and Programming 24

Binary Numbers 28 -February-2007 0000 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 CMP 131 Introduction to Computers and Programming 25

Binary Addition 1010 + 0101 = ----1111 10 + 5= -----15 1010 + 0111 = ----0001 10 + 7= -----17 => 1 28 -February-2007 1010 + 0011 = 3 = -----1101 13 OVERFLOW!!! CMP 131 Introduction to Computers and Programming 26

Other Number Systems • Hexadecimal: base 16 – Each digit can hold 16 values (0 -9, A-F) – Ex: A 02 F – 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? 28 -February-2007 CMP 131 Introduction to Computers and Programming 27

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-2007 CMP 131 Introduction to Computers and Programming 28