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Chapter 1

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Ryerson University
Information Technology Management
ITM 200

Chapter 1: Solving problems with computers What is a computer? Hardware: you can physically check; CPU, memory, hard disk, floppy disk, monitor, printer, communication devices Software: instructions to the computer, without programs a computer is an empty machine- computers do not understand human languages -Computers execute instructions to process data. CPU: central processing unit which are built as a single microprocessor chip. Each chip is associated with a set of instructions (Machine Code) which it can execute. Binary Bit Patterns: strings of 0 and 1’s, like a switch. Each instruction and the data are stored as binary patterns; any given computer can only execute instructions in the machine code language of its microprocessor  A machine code computer program consists of binary codes for instructions. The program can be stored on a disk. To execute the program, it is loaded from the disk into the computer’s internal memory, then the instructions are fetched one by one by the microprocessor(CPU) and executed  Disadvantages of Machine Codes: time consuming, meaningless to human readers, not portable Assembler Language: little words (mnemonics) are used, each of which corresponds to one of the machine code instructions. Data can be represented using decimal numbers instead of binary. Example, load number 5 = LD 5 instead of 00100010010.  A program named an Assembler is required to TRANSLATE an assembler language program into machine code  Disadvantages: still not portable and obsolete rd High Level Languages: 3 generation programming languages that were more abstract, problem oriented instructions. Examples: C++, Java, Modula-2/3, Simula, Pascal, Ada, Algol, FORTRAN, Cobol  Made programming less error prone and more productive but they could not be executed on a computer, they had to be stored as character codes, then translated into the machine code for the required processor  A program called the Compiler, checks for any syntax (spelling and grammar) of the high level language and reports any errors. It then creates a machine code version of the high level program. Once this is done, the machine code may be executed on the host machine without the compiler being present  Compilers are need to port source programs to any machine. Recompiling is essential for different platforms. Computers are networked to work together.  A program in high level language is called a source program, computers cannot understand source programs, therefore a compiler translates the source program (linked with supporting library codes)  Bootstrapping: in order to run on a computer, a compiler must be written in machine code. It’s hard to write a compiler in low level language there a compiler is written in high level. Therefore, we need to compile the complier which someone has to make a compiler written in machine code first.Java  Developed by Sun Microsystem Inc, made in 1991 by James Gosling and Bill Joy  Java program is just a text file, it contains letters, numbers, and symbols= source code file  In order to create a program, the java complier will require the filename of the java source (which would be made in Notepad) to end in “.java”. The program text is then fed into the Java complier, if there is no errors the output will be a file containing the compiled byte code programmed, ready to run. To run the program, the “.class” file is fed into the run time interpreter.  Java was designed to run object programs on any platform. With java, you write the program once and compile the source program into a special type of obje
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