BACS 287 Basics of Programming BACS 287

History of Computers Early “computers” mechanized the calculation process Charles Babbage designed the analytical engine - first with stored memory in early 1800s Herman Hollerith built a punched card tabulating machine in 1880s None of these were “true” computers Abacus - earliest computing devices - ancient Egypt and China 1st mechanical adding machine - add and subtract - 1642 Blaise Pascal 1st mechanical calculating machine - multiple and divide too - Gottfried Liebnitz 1692 Charles Babbage - professor of mathematics at Cambridge - Difference engine - perform calculations and print results without human intervention - Analytical Engine - designed but not built - had memory unit, arithmetic unit, punched card input Herman Hollerith - tabulating machine - process US census in 1890 1896 the Tabulating Machine Company that later merged with 12 other companies to form IBM None of these were true computers because they did not have a way to internally store its own program and memory. BACS 287

History of Computers First true computers developed during W.W.II EGNIMA - early 1940s Colossus - early 1940s MARK I - 1944 ENIAC - 1946 EDVAC, EDSAC - 1949 UNIVAC I - 1951 EGNIMA was German code machine, not true computer Colossus was British counter machine to break German code MARK I was essentially Babbage difference engine. Had program entry via punched paper tape. ENIAC (Electronic Numerical Integrator and Calculator) 1st US computer. Did not use stored program - used wire board. EDVAC (U.S.) , EDSAC (Electronic Delay Storage Automatic Computer) - (England) had internally stored programs UNIVAC I - First commercial system. Delivered to census in 1951. First business use was GE in 1954 IBM 650 - 1954 first commercial computer for IBM IBM dominance did not take off until 1960 with IBM 1401 followed by the IBM 360. UNIVAC I and IBM 650 were 1st generation hardware BACS 287

Hardware/Software Generations 1st Generation Hardware Vacuum tubes Punched cards, Paper tape Magnetic tape available Machine language Millisecond access time 1st Generation Software Machine language Specific to CPU tedious, error prone time consuming 1-to-1 instruction ratio explicit control fast execution (within hardware limitations) BACS 287

Hardware/Software Generations 2nd Generation Hardware Discrete Transistors Punched Cards, paper tape Magnetic tape Assembly language Microsecond access time 2nd Generation Software Assembly language mnemonics symbolic names relocatable code explicit control usually 1-to-1 instruction ratio fast (within hardware limitations) BACS 287

Hardware/Software Generations 3rd Generation Hardware Integrated circuits Magnetic Disk High-level languages (COBOL,Fortran...) > 100 Nanosecond access time 3rd Generation Software High-level languages portable between machines instruction explosion relatively English-like problem specific less control less speed than low level languages BACS 287

Hardware/Software Generations 4th Generation Hardware (...) large scale Integrated circuits Mass Storage devices 4th Generation languages (Easytrieve, Mapper) 1-10 Nanosecond access time 4th Generation Software (...) 4th generation less procedural, more problem oriented graphically oriented built-in code generation facilities less control less speed than low level BACS 287

Hardware Hardware are the physical devices that make up a computer system Hardware systems are “tuned” to work together There are five basic hardware components in a computer system BACS 287

Hardware Components of a Computer System Input & Output Devices Central Processing Unit (CPU) Primary Storage (RAM) Secondary Storage (disk) Communication Devices BACS 287

CPU The “brains” of the computer Executes instructions to perform simple functions Capable of executing only one instruction at a time Executes instructions in billionths of a second (i.e., nanoseconds) Composed of several sub-components BACS 287

CPU Sub-Components Control Unit (CU) Arithmetic and Logic Unit (ALU) Registers Cache memory Clock and others... BACS 287

Primary Storage Random Access Memory (RAM) Volatile storage All computer programs must be in RAM before the CPU can execute them Access time normally measured in nanoseconds (billionth of a second) Relatively limited amount of RAM in a system BACS 287

Secondary Storage Hard disks, floppy disks, tape, ... Non-Volatile storage Large Capacity -- Relatively Slow Most rely on moving parts Access time normally measured in thousandths of a second (milliseconds) Speed difference between RAM and Disk is tremendous BACS 287

Software Software is the logical component of a computer system Software are detailed instructions (procedural logic) that tell the CPU how to solve a problem There are various levels (types) of software; each has a specific purpose The three types are 1) operating systems, 2) compilers and interpreters, and 3) application programs BACS 287

Operating System A program that works directly with the hardware Provides useful services that application programs need Usually written in low level languages (e.g., assembler, C) to work on a specific CPU “Windows” is an operating system BACS 287

Compilers and Interpreters Utilities to translate English-like source code into executable object code for the CPU Compilers translate the entire program as a unit and save the results Interpreters translate one line at a time and discard the results after execution Visual Basic can be both an interpreter and a compiler. BACS 287

Application Programs Application programs are software that perform end-user tasks Normally, high-level and very specific (e.g., spreadsheet, word processor) You can write applications programs using Visual Basic and other computer languages BACS 287

Where this class fits into the picture In this class you use a compiler (& interpreter) running under the control of the operating system (on the hardware) to write application programs. Generally speaking, it is incorrect to say that you are “programming” when you use an application program (like Excel or Access). Programmers write new applications; they don’t utilize existing packages. BACS 287

Quiz What is the difference between hardware and software? What are the 5 components of a “true” computer? What is the difference between a compiler and an interpreter? What is the main difference between primary storage and secondary storage? What is the main difference between 2nd generation and 3rd generation programming languages? BACS 287