1.2.2 System Application Generation

Question 1

What is Software

Answer 1

The programs / sets of instructions that run on a computer system.

Question 2

What are the 3 categories that software falls into

Answer 2

• Application
• Utility
• System

Question 3

What is Application Software

Answer 3

• Application Software is any software package that carries out a task and/or aids the user in producing something on a computer
• It is designed to be used by the end-user to perform either generic or specific tasks (desktop publishing, word processors, spreadsheets)

Question 4

Why pick 1 application over the other

Answer 4

• Easy of use
• Cost
• Speed
• Hardware

Question 5

What is source code

Answer 5

• Source code is produced by developer’s and defines what they want their software to do
• Easy to understand, maintain and debug for humans not computers
• When software is described as open or closed it refers to if it is public or not

Question 6

What is system software

Answer 6

• Low level software that is responsible for running the computer system smoothly, interacting with hardware and generally providing a platform for applications to run

Question 7

What is open-source software

Answer 7

Source code is freely available… …for others to amend / examine / recompile

Question 8

What is closed- source software

Answer 8

• Protected by the copyright Design and Patents Act
• Users cant modify the software
• Usually paid for and licensed per user or per computer
• Tested by developer’s prior to release, although it may run better programs

Question 9

What are the benefits of open source for the user

Answer 9

• Software is free
• Wide community modification and support and improved by anyone

Question 10

What are the benefits of open source for the creator

Answer 10

• Gets their software out to the wider community
• This means that a lot of the core functionality they need is already available (1) so the company just has to make amendments/additions specific to their system (1) saving time and money (1).

Question 11

What are the disadvantages of open source software for the user

Answer 11

• Can be poorly supported
• Some features might not be well tested

Question 12

What are the disdvantages of creators for open source

Answer 12

• Little-to-no financial gain

Question 13

What are the advantages of closer source for the creator and the user

Answer 13

• Well supported tested and professional built product
• They recieve an income for their product

Question 14

What are the disadvantages of closed source for the user and creator

Answer 14

• Cost or ongoing subscription fee
• Constant demand from community for more features and improvements
• Piracy issues

Question 15

What is a knowledge based system

Answer 15

• Using a knowledge based system, a user can interrogate a vast knowledge base to find a solution
• The user enters the information they already have, and the knowledge based system infers an answer
• If the system cant reach a conclusion, it requests more information
• This process is continued until either the system has a high degree of confidence that it knows the solution or it has exhausted every line of inquiry that it doesnt know the solution

Question 16

What are the different parts that make a knowledge based system

Answer 16

• Knowledge base : a database containing expert knowledge
• Inference Engine : Attempts to work out the answer to the user’s query by using the rule base
• Rule Base: Links knowledge together through facts
• User Interface: Allows the user to communicate with the system (HCI) stands for human computer inteface

Question 17

What 3 decisions is the inference engine responsibke for

Answer 17

• Whether it has enough information to arrive at an answer
• Whether it requires more information
• Whether it cant reliably come up with an answer

Question 18

What does CAD stand for and what is it

Answer 18

• Computer Aided Design
• Enables designers to try out different designs for a product before physical production
• Allows the designer to place parts together, scale to test how the design might react in the real world without making physical prototypes e.g designing a car.

Question 19

What does CAM stand for and what is it

Answer 19

• Computer Aided Manufactuing
• Machines make products rather than people making them (small error margin)
• Specifications are fed into CAM systems, which drives an assembly line
• The specification say exactly what the product looks like, its materials and the steps required to assemble it
• It relies heavily on sensors and actuators

Question 20

What is utility software

Answer 20

• A piece of software … – … with one purpose … – usually to do with the upkeep / maintenance of a computer.

Question 21

What are the 4 main areas that utility software can be split into

Answer 21

• File manager utility software
• Compression software
• Task Manager
• Anti-virus Software

Question 22

What does file manager do

Answer 22

–Manages data storage / organises data storage

– Used for the deletion / sorting / moving / copying / creation of files / folders – Manage the storage of software

Question 23

What is compression software

Answer 23

• Reduces software and the overall size of files
• Will complete this with lossless compression
• Compressed files are unreadable until uncompressed by the same utility
• A number of different files, folders and executables can be comprssed together, to create a single compressed file. The compression utility will retain files, details and structure

Question 24

What is Anti-Virus software

Answer 24

• Anti-virus protects the system, scans system, alerts the user and deletes viruses found

Question 25

What do Task Managers do

Answer 25

* Allow the user to view the processes currently running on a system and see what resources each one is using.

Question 26

What are translators and what are the 3 types

Answer 26

* The term translator is used to cover all the types of software that converts code from 1 form to another (high level source code into low-level object code) * Compiler * Interpreter * Assembler

Question 27

What is a compiler

Answer 27

* **Converts source code** written in high-level languages into object code then machine code **all at once** after carrying out a number of check and errors. * Whole code translated before it is run

Question 28

What is an interpreter

Answer 28

* It translates each line of code into machine code, line by line * Takes the first line of machine code, translates it and executes it before moving onto the next

Question 29

What is an Assembler

Answer 29

* Assemblers translate assembly code into machine code * Each assembly code instruction has a 1-1 mapping with machine code instruction (1 instruction = 1 line of machine code)

Question 30

What are the 2 phases of assembly code into machine code. What is the work needed to be done before the CPU can execute

Answer 30

* The assembly code contains variables, labels and are converted into machine code in a 2 phase process * Phase 1: Labels and variables are converted into memory addresses and stored in a symbol table * Variables map to the memory location that s used to store the value, lables map to the exact position of the instruction it needs to jump to * Phase 2: Converts the mnemonics into their binary representation

Question 31

What is a symbol table

Answer 31

* A symbol table is produced as the assembler works through its first phase * In order to store a variable (COUNT) an address must be set up in the next available memory address after the prgram * When a label is encountered, the memory address of where it was defined is placed in the symbol table * Once it has been produced the assembler goes over the code and replaces every variable/label with its memory address

Question 32

As programmers what would we like a our source code to be like

Answer 32

* Close to english * Easily read, modified and interpreted by humans

Question 33

What are the 4 main stages of compiliation

Answer 33

* Lexical Analysis * Syntax Analysis * Code Generation * Code Optimisation

Question 34

What happens in Lexical Analysis (First Stage)

Answer 34

* Each line is read and the compiler converts lexemes into a series of tokens * A pair is created: token (type of data lexeme is) (variables, constants) and the lexeme (component of source code). * White space (extra lines) are stripped out. Encountering white space, operator or symbol - lexeme is complete * It then checks if the lexeme is valid using a predefined set of rules that allow every lexeme to be indentified as a valid token * Variables, and subroutines stored in symbol table

Question 35

Explain what type of software you would classify compression as

Answer 35

* A compression program is a utility. It is a small program with 1 purpose and helps with system upkeep

Question 36

State 3 roles of the Operating System

Answer 36

* Manages Hardware of the system * Manages programs installed and being run * Manages Security of the system * Provides an interface between the user and the computer

Question 37

What happens in Syntax Analysis (second)

Answer 37

* Checks if tokens are in the right order and follow rules of language * Does this by analysing token stream against production rules to **detect any errors** and builds an **abstract syntax tree** (abstract syntactic structure of source code) - follows syntax diagrams to check everything is correct * When an identifier is added, symbol table is checked to see if it exists * Information from AST is used to update data type of identifiers * Where it breaks the rules of the language errors are generated. If no rules are broken then it’s passed on to the next stage…

Question 38

What is syntax

Answer 38

* The rules governing the arrangement of words and phrases to create well-formed sentences

Question 39

What is the Machine Code Generation Stage of Compiliation (third) First part of this stage

Answer 39

* Can only start when AST is made (no errors) * Is done by mapping parts of the AST to blocks of machine code - blocks are known as machine templates * The compiler will look for common tasks and match to machine code templates * Code mapping is done by finding common AST patterns and matching to blocks of machine code - continues until whole tree is mapped

Question 40

What is the Machine Code Generation (2nd part of this stage

Answer 40

* Once we are at a low-level language, can make use of architecture of CPU such as general registers (to minimise memory access) * General registers are assigned to parts of the code * There arent enough registers - will be recycled as program is executed * Machine code generation must decide to what registers are assigned to which instructions

Question 41

What is Machine Code Optimisation

Answer 41

* It attempts to reduce the execution time of the program and use little memory as possible by: * Spotting redundant instructions and producing object code that achieves the same effect as the source program but may not by same means * Remove subroutines that are never called * Removing variables and constants that are never referenced * Removes the number of jumps/branches code makes

Question 42

What are library modules

Answer 42

* Libraries are compiled, error free pieces of software written by expert programmers so save time developing and testing modules * They contain useful routines which perform common tasks such as sorting or searching encryption and graphics

Question 43

Why does using a library help programmers

Answer 43

* Relatively error free/ has already been tested * Ready to use / saves time/already been written * Used multiple times / common tasks / reduces repeated code * Programmer expertise * Different source languages

Question 44

What are the drawbacks of library modules

Answer 44

* May (significantly) increase size of compiled file * as library contains many routines that aren‘t being used. * Not written by the programmer …so introduces uncertainty / require further testing /programmer needs to spend time familiarisingthemselves with it

Question 45

What are linkers

Answer 45

* Links the main program to libraries ..can either include them in the final executablecode ..or get the executable code to point to the externallibraries * There are 2 methods to pull in the libraries it needs: * Static Linking * Dynamic Linking

Question 46

What is Static Linking

Answer 46

* All required code from the libraries is included directly in the finshed machine code - results in large executable program files

Question 47

What is Dynamic Linking

Answer 47

* Compiled versions of the required libraries are stored in the host computer. * The OS links the required code from the library as the prgram is running * This cuts down on the size of the compiled machine code, if the dynamic libraries change, the program may stop

Question 48

What are loaders

Answer 48

* The loader is a small utility that will load the Direct Link Library (DLL) file on request , rather than linking it when it is being compiled * It is part of the OS that loads the executable program file (machine code) into memory, ready to be run * When using Dynamic Linking, it will also be responsible for loading the required libraries into memory

Question 49

What are the different software that can be used

Answer 49

* Presentation Software - convey info. Used in meeting/educational. * Desktop Publishing - creation of publication. Templates. * Spreadsheet Packages - numbers/financial information * Word Processor * Drawing Packages - Allow user to draw images Bitmap: uses pixels, Vector: made of lines/shapes can be resized without loss of quality. * Database Packages: Data organised into tables, fields/records. Search and sort data quickly.

Question 50

What are the advantages of CAM

Answer 50

* They will always produce products that are exactly the same * Dont get tired * Dont make mistakes (unless they break down) * Work 24 hours of the day

Question 51

Exam Question: How does an application differ from a utility

Answer 51

* Application performs tasks for the user (rather than the computer) * Performs generic (rather than specific tasks)

Question 52

Advantages of a Compiler

Answer 52

* No need for translation at run time * Speed of execution is faster * Code is usually optimised * Original source code is kept secret

Question 53

What are the disadvantages of a compiler

Answer 53

* Program will not run with syntax errors, makes it more difficult to write code * Code needs to be recompiled when the code is changed * Designed for a specific type of processor

Question 54

Advantages of an interpreter

Answer 54

* Easy to write source code as the program will run and stop when it finds a syntax error * Code doesnt need to be recompiled when code is changed

Question 55

Disadvantages of an Interpreter

Answer 55

* Translation software is required at run-time * Speed of execution is slower * Code is not optimised * Source code is required

Question 56

Exam Question: Describe what is meant by the term Javascript (2)

Answer 56

* A programming language that runs in a web browser (1) * that can be embedded into HTML (1) * with tag (1) * to add interactivity to a page (1)

Question 57

Exam Question: Explain how Linux being open-source would benefit the games company

Answer 57

* This means that a lot of the core functionality they need is already available (1) * so the company just has to make amendments / additions specific to their system (1) * saving time and money (1).

Question 58

What is a device driver?

Answer 58

* Used to configure hardware * To enable peripheral and OS to communicate

Question 59

What are the differences between open source and closed source?

Answer 59

* – Open source has the source code freely available… – … * to amend/copy/redistribute/recompile – * Whereas closed source is distributed in binary form only/the source code is not made available… * – There are licensing conditions restricting the redistribution/there is no permission to amend the (program) code

Question 60

What is the purpose of the lexical and syntax analysis stages?

Answer 60

* Lexical analysis is necessary to put the code into a format which can be read and processed (i.e. parsed) by the syntax analyser. * Syntax Analysis is necessary to ensure the code is valid in as much as it meets all the structural rules of the language. This guarantees it will run (though it might not do as expected and may still have occurrences of runtime errors).

Question 61

What is the purpose of the machine code generation and machine code optimisation stages?

Answer 61

* Code generation is necessary to turn the code into a format that the processor can understand (i.e. binary machine code). The code optimisation whilst not necessary, does ensure the code runs quicker or using less memory.

Question 62

What is the purpose of a linker?

Answer 62

* Linking is necessary to ensure the library code is incorporated into the final program.

Question 63

Exam Question: What is syntax analysis stage? (5)

Answer 63

* Statements / tokens are checked * against the rules / grammar of the language * Errors reported as a list * Error diagnostics given * Detail added to symbol table… …eg data type / scope / address * Receives output from lexical analysis / passes code to code generation

Question 64

Exam Question: Early computers were programmed in binary machine code. Today most programmers use high-level languages. Explain why the programmer could use intermediate code for the final product.

Answer 64

* Can be used in a virtual machine * Portable/ can be used on any machine * Protects the source code from being copied