What is a Computer? Computer Device capable of performing computations and making logical decisions Computers process data under the control of sets of instructions called computer programs Personal computers: economical enough for individual Distributed computing: computing distributed over networks Client/server computing: sharing of information across computer networks between file servers and clients (personal computers) Dale Roberts
What is a Computer? (cont. ) Computer Hardware Various devices comprising a computer: Keyboard, screen, mouse, disks, memory, CD-ROM, and processing units Hardware Trends: every year or two the following approximately double: Amount of memory in which to execute programs Amount of secondary storage (such as disk storage) Used to hold programs and data over the longer term Processor speeds User High-level Language Application Software Assembly Language The speeds at which computers execute their programs Computer Software Computer Programs that run on a computer, including Operation System (OS) Application Software Computer Language OS Firmware Machine Code Hardware
What is a Computer? (cont. ) Internet The Internet enables Quick and easy communication via e-mail International networking of computers Packet switching The transfer of digital data via small packets Allows multiple users to send and receive data simultaneously No centralized control If one part of the Internet fails, other parts can still operate Bandwidth Information carrying capacity of communications lines Ex: Internet T 2 at IUPUI World Wide Web Locate and view multimedia-based documents on almost any subject Makes information instantly and conveniently accessible worldwide Possible for individuals and small businesses to get worldwide exposure Changing the way business is done
Computer Organization A Typical Von-Neumann Architecture CPU Control Circuit (ex: PC: Program Counter) ALU Example: 1. 2. 3. 4. 5. 6. Input unit Output unit Memory unit Arithmetic and logic unit (ALU) Central processing unit (CPU) Secondary storage unit Memory I/O
Computer Organization (cont. ) Six logical units in every computer: 1. Input unit Obtains information from input devices (keyboard, mouse) 2. Output unit Outputs information (to screen, to printer, to control other devices) 3. Memory unit Rapid access, low capacity, stores input information ROM (Read Only Memory): CMOS, EPROM … RAM (Random Access Memory): SRAM, DRAM, SIMM, DIMM … 4. Arithmetic and logic unit (ALU) Performs arithmetic calculations (addition, subtraction. . . ) and logic decisions 5. Central processing unit (CPU) Supervises and coordinates the other sections of the computer 6. Secondary storage unit Cheap, long-term, high-capacity storage Stores inactive programs
Computer Organization (cont. ) Central Processing Unit (CPU), “brain” of a computer, consisting of Arithmetic and logic unit (ALU): performs arithmetic calculations (addition, subtraction. . . ) and logic decisions (>, <, =, . . . ) Control Unit (CU): decodes each machine instruction and sends signal to other components for carrying out the instruction. An integrated circuit (IC) that is a full central processing is call microprocessor ( p); a CPU’s current instruction and data values are stored temporally inside the CPU in special high-speed memory location called registers. CPU speed: ? MHz (M: Mega = 106, Hz=1/sec); Memory A large collection of circuits, each capable of storing bit Cells (words): manageable units; typical size is 8 bits (1 byte), some machines are 16 bits (2 byte) and some are 32 bits or 64 bits Byte (8 bits), KB (kilobyte, 210 byte 103), MB (Megabyte, 220 byte 106), GB (Gigabyte, 230 byte 109)
Computer Organization (cont. ) Computer memory is comparable to a collection of numbered mailboxes. To identify individual cells in a machine’s main memory, each cell is assigned a unique name, called its address ASCII Data Address H 01001000 0101 e l l o , 01100101 01101100 01101111 00101110 0000 0111 0000 1000 0001 . . . 0001 0010 Address Bus Data Bus The organization of byte-size memory cell Most Significant Bit (MSB) High-order end Least Significant Bit (LSB) 0 0 0 1 Low-order end
Operation System (OS) Responsibilities: Command-line Interface Communicating with the computer user UNIX MS_DOS Managing allocation of memory, of processor OS/2 VMS time, and of other resources for various tasks I/O handling: BIOS v. s. DOS services (Interrupts) Read/Write data from secondary storage Graphical User Interface (GUI) Mac. OS Windows X Windows Evolution of Operating Systems Batch processing: do only one job or task at a time Operating systems: manage transitions between jobs and Increase throughput (amount of work computers process) Multiprogramming: Computer resources are shared by many jobs or tasks Timesharing: Computer runs a small portion of one user’s job then moves on to service the next user
Application Software Developed to assist a computer user in accomplishing special tasks ex: word processing applications: MS-word or Word -perfect ex: Spreadsheet applications: Lotus 1 -2 -3, Excel ex: Database: Oracle, MS-Access Software Development Method Problem: specify the problem requirements Analysis: analyze the problem Design: design the algorithm to solve the problem Implementation: Implement the algorithm Testing: test and verify the completed program Maintenance: maintain and update the program
Programming Languages 1. Machine languages (machine dependent) Native tongue of a particular kind of computer. Each instruction is a binary string. The code is used to indicate the operations to be performed and the memory cells to be addressed. This form is easiest form of computers to understand, but is most difficult for a person to understand. Strings of numbers giving machine specific instructions Example: +1300042774 +1400593419 +1200274027 2. Assembly languages (machine dependent) English-like abbreviations representing elementary computer operations (translated via assemblers) Again specific to only one type of computer. Uses descriptive names for operations and data, e. g. , “LOAD value”, “ADD delta”, “STORE value”. Assemblers will translate these to machine languages. Intermediate level. Somewhat descriptive, but basically following the machine instructions. Example: LOAD BASEPAY ADD STORE OVERPAY GROSSPAY
Programming Languages (cont. ) 3. High-level languages (machine independent) Codes similar to everyday English High-level languages: Write program instructions called statement that resemble a limited version of English. e. g. , the statement “value= value + delta”. Portable, meaning it can be used on different types of computers without modifications. Compilers translate them to machine languages. Examples are FORTRAN, PASCAL, COBOL, C, C++, BASIC etc. Use mathematical notations (translated via compilers) Example: gross. Pay = base. Pay + over. Time. Pay Before b Example: Statement: a a= a + b a After b 10 7 17 7
Programming Languages (cont. ) Structured programming Disciplined approach to writing programs Clear, easy to test and debug and easy to modify Multitasking Specifying that many activities run in parallel (still timesliced) Language FORTRAN COBOL Lisp C Prolog Ada Smalltalk C++ JAVA Application Area Scientific programming Business data Processing Artificial Intelligence (AI) System Programming AI Real-time distributed systems GUI, OOP Supports object & OOP Supports. Web programming Origin of Name Formula Translation Common Business-Oriented Language List Processing Predecessor B Logic Programming Ada Augusta Byron & Charles Babbage Objects “talk” via message C (++ is the increment operator) Originally named “Oak”
Semantic Gap A “semantic gap” exists between the amount of information conveyed in assembly language v high level languages. Consider the following C single statement: x = x + 3; This single statement may require many assembly language statements (operations): Load memory location 24 into accumulator Add a constant 3 to the accumulator Store accumulator in memory location 24 The number of executable statement expands greatly during the translation process from a high level language into assembly language.
C Programming Language C High-level general-purpose language developed in 1972 at AT&T Bell Lab. By Dennis Ritchie from two previous programming BCPL and B Originally developed to write the UNIX operating system Hardware independent (portable) By late 1970's C had evolved to "Traditional C" Today, virtually all new operating systems are written in C or C+. The current standard in C is ANSI C. C++ is a more advanced version of C, incorporating among other things, the object-oriented constructs Standardization Many slight variations of C existed, and were incompatible Committee formed to create a "unambiguous, machine-independent" definition Standard created in 1989, updated in 1999 C has become a popular language industry due its power and flexibility
The C Standard Library C programs consist of pieces/modules called functions A programmer can create his own functions Advantage: the programmer knows exactly how it works Disadvantage: time consuming Programmers will often use the C library functions Use these as building blocks Avoid re-inventing the wheel If a premade function exists, generally best to use it rather than write your own Library functions carefully written, efficient, and portable The Key Software Trend: Objects in C++ and JAVA Reusable software components that model items in the real world Meaningful software units: ex: Date objects, time objects, audio objects, video objects, file objects, record objects…any noun can be represented as an object More understandable, better organized, and easier to maintain than procedural programming Favor modularity
A Typical C Program Development Environment • Phases of C Programs: Editor Disk Preprocessor Disk Compiler Disk Linker Disk 1. Program is created in the editor and stored on disk 2. Preprocessor program processes the code 3. Compiler creates object code and stores it on disk. 4. Linker links the object code with the libraries Primary Memory Loader 5. Loader puts program in memory. Disk Primary Memory CPU 6. CPU takes each instruction and executes it, possibly storing new data values as the program executes 1. Edit 2. Preprocess 3. Compile 4. Link 5. Load 6. Execute
A Typical C Program Development Environment (cont. ) • Procedure to Prepare a C Program for Execution Enter the program code and save as a source (*. c) file using Word Processor (editor) Source (. c) file on disk (Format: text) Compiler attempts to translate the program into machine code Success New object (*. obj) files (Format: binary) The linker links the new object file with other object files Failure Revised source file Correct syntax errors List of errors Other object (*. obj) files Input data Executable (*. exe, *. out) file (Format: binary) The loader places the executable file into memory Executable program in memory Welcome to CSCI 230 Results
Constructs in C Language Type Declarations: ex: int, float, … I/O: ex: printf(), scanf() Arithmetic and Logical Operations: ex: +, -, *, /, %, >, <, ==, … Arrays, Pointers, Structures, Unions, … Functions Arguments & return values Recursion Control Mechanisms: ex: if, else, while, for, … Characters & Strings: ex: strcat(), strcpy(), … File Processing: ex: fopen(), fclose(), … Pre-processor: ex: #define … Misc. bit operations, . . .
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