Foundations of Comp Science
Foundations of Comp Science CSC 150
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This 0 page Study Guide was uploaded by Mona D'Amore on Monday November 2, 2015. The Study Guide belongs to CSC 150 at Concordia University Wisconsin taught by Staff in Fall. Since its upload, it has received 35 views. For similar materials see /class/234349/csc-150-concordia-university-wisconsin in ComputerScienence at Concordia University Wisconsin.
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Date Created: 11/02/15
Computers use algorithms to solve problems An algorithm is a detailed every step must be stated and unambiguous every step must be perfectly clear set of step by step procedures for solving a problem Algorithms are general purpose in that they are the general manner to solve speci c problems because no data is hardcoded into the instructions and the data is represented symbolically using a eld a spreadsheet cell address or a variable name The process activity is the key to understanding how a computer actually solves problems The processor unit contains the CPU and memory which are the two major HW components needed for processing The CPU controls all the H W and performs the actual processing Memory is the working space for the CPU as everything for processing must be in memory The CPU is a single chip but is divided into the CU control unit and the ALU arithmeticlogic unit For every SW instruction the CU must Fetch get the instruction from memory Decode determine what that instruction means and Execute inform the correct HW device what to do it This is an algorithm telling the computer how to follow an algorithm In essence the CU runs SW The ALU is the part of the processor that actually performs the processing Memory is the second major HW component needed for processing The fundamental unit of memory is a byte Each byte of memory has its own address The S W field is placeholder and descriptor of what is in memory As a placeholder it reserves a byte of memory and remembers its address Everything the CPU is processing is in memory This is why the amount of storage space containing stuff doesn t effect the speed ofprocessing The only language the computer understands is binary The 0 and 1 represent the two positions a CPU switch can be in on or off There are several different forms of binary Numbers are represented in base 2 They are typically written in groups of eight binary digits because a group of eight bits forms one byte measure of storage or memory Characters are represented in ASCII Instructions are represented in ML machine language A programming language is a collection of possible instructions for the CPU and programmers used them to create application packages Programmers use High Level Languages HLL to make programming easier Because a HLL uses words and symbols it is much closer to English than the ones and zeros of ML The computer can t understand a HLL however so it must be translated to ML The computer performs this translation through the HLL to ML dictionary This is a file that contains all the HLL statements and all the equivalent ML binary patterns Through the request information use of data the SML CSC 150 study guide 3 computer nds the HLL statement that the programmer entered and converts it to the associated ML statement This translation is possible because HLL has a limited syntax only certain forms are allowed to represent expressions and exact semantics every HLL statement has only one meaning in ML Because the computer performs this translation a HLL can be used on different types of computers it s portable Programming is level one problem solving because the programmer is creating algorithms The steps in programming notice that the first three are level 1 problem solving and the last is level 2 Understand the problem Without a total understanding of the problem the algorithms to solve that problem cannot be created Plan the solution Use Pseudocode an algorithm written in a human language to develop an outline Create code an algorithm written in a computer language Test the application S W applications don t interact directly with the HW Systems S W controls all the HW and makes using it easier for users and other S W One kind of Systems SW is Translation SW Translation SW contains the dictionary that translates HLL to ML There are two kinds of translation SW Interpreter translates one HLL statement executes that statement repeats until all statements have been translated and executed Compiler all HLL statements are translated into a group of ML that group is saved as a file for execution A compiled application is faster than an interpreted one and it requires no translation SW to run it because it s already been changed to ML Another kind of Systems SW is Booting SW Booting SW is the start up instructions for the computer It performs the selftest of the HW and loads the Operating System OS Because the instructions a computer is processing must be in memory and RAM memory is erased when the power supply is cut off Booting SW must be in ROM Booting SW loads the OS which controls and manages all the HW and other S W in the system The OS is a command interpreter It inputs interpreters and executes each user command could be an OS command like an application package s file name etc The OS is the interface between HW and other SW The OS is a resource manager It manages the use of scarce resources This is the most important job of a large computer OS SML CSC 150 study guide 3 On a large computer system the scarce resources are the CPU and memory The OS manages memory through the use of virtual memory which gives the appearance of unlimited RAM memory The OS manages the use of the CPU by multitasking which gives the appearance of multiple simultaneous users There are four steps in multitasking The OS gives the rst user a very small time slice to use the CPU The CPU executes that user s application during that time slice When that time is up the application is put on hold This process continues in a Round Robin fashion Storage is a nonvolatile long term repository for stuff Because the data is not stored electronically it is not erased by a loss of electricity Drive and Media are the two HW components needed for storage The media physically holds the data One kind of media is disc media e g oppy disc The disc media itself is round and is divided into tracks and sectors so data can be accessed randomly The drive is what allows the CPU to access stuff from the media A disc drive spins the disc media to access any sector and the readwrite head moves to access any track In xed media storage the media and the drive are one unit and the media cannot be removed e g a hard drive This is more convenient than removable media because the stuff in xed storage is always online In removable media storage the drive and media are separate and the media can be removed like a oppy disc This allows the user to transport the stuff in storage to other machines This is more vital than having storage permanently online File is the generic name give to any logical thing on storage A le association tells the computer to run an application when an associated le is accessed A le extension indicates what kind of le it is executable or non executable To run an executable le the OS has to load it In order to load it the OS must know where that le is located on storage In disc storage the OS locates the le randomly by knowing its tracldsector address Data les nonexecutable can be accessed sequentially or randomly Sequential access les store records in key eld order To nd a certain one all the records must be searched In a random access le the records are located directly through the use of hashing algorithms SML CSC 150 study guide 3
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