CMP 131 Introduction to Computer Programming

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

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

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

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

5. 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 CMP 131 Introduction to Computers and Programming

6. 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++ CMP 131 Introduction to Computers and Programming

7. 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 CMP 131 Introduction to Computers and Programming

8. 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 CMP 131 Introduction to Computers and Programming

9. 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. CMP 131 Introduction to Computers and Programming

10. 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?? CMP 131 Introduction to Computers and Programming

11. 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 MainMemory CMP 131 Introduction to Computers and Programming

12. 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. CMP 131 Introduction to Computers and Programming

13. 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 CMP 131 Introduction to Computers and Programming

14. 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 CMP 131 Introduction to Computers and Programming

15. 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 CMP 131 Introduction to Computers and Programming

16. 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 CMP 131 Introduction to Computers and Programming

17. 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 CMP 131 Introduction to Computers and Programming

18. 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 accessURL = Uniform Resource Locator • Dynamic web pages for e-commerce (Perl, JAVA, etc.) • Security • Performance (multiple clients) • Offloading work to client CMP 131 Introduction to Computers and Programming

19. 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 CMP 131 Introduction to Computers and Programming

20. 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 CMP 131 Introduction to Computers and Programming

21. 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 CMP 131 Introduction to Computers and Programming

22. 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 CMP 131 Introduction to Computers and Programming

23. 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 CMP 131 Introduction to Computers and Programming

24. 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 CMP 131 Introduction to Computers and Programming

25. Binary Numbers CMP 131 Introduction to Computers and Programming

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

27. 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? CMP 131 Introduction to Computers and Programming

28. 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 CMP 131 Introduction to Computers and Programming