1.2.2: Application Generation

Question 1

System Software

Answer 1

• low level software that is responsible for running system smoothly interacting with hardware–> providing platform for apps
• user not directly interacting with S.S –> ensures high performance for user

Question 2

System Software examples

Answer 2

• library programs, utility programs, O.S, device drivers

Question 3

Application Software

Answer 3

• designed to be used by the end-user to perform 1 specific task
• requires systems software to run

Question 4

Application Software examples

Answer 4

-desktop publisher, word programs, web browser

Question 5

Utilities

Answer 5

-ensuring the consistent high performance of the OS

-each utility program has a specific function –> linked to maintenance of OS

Question 6

(U) Compression

Answer 6

-OS provide utilities –> allow files to be compressed/ decompressed

-compressing large files over internet + compress large files

Question 7

(U) Disk defragmentation

Answer 7

• as hard disk becomes full, read/write times slow down –> files become fragmented as they are stored in different parts of memory
• rearranges contents in hard drive –> access faster –> improving performance

Question 8

(U) Antivirus

Answer 8

• deleting threats + alerting user

Question 9

(U) automatic updating

Answer 9

• OS needs to up to date
• tackles bugs/security flaws –> less vulnerable

Question 10

(U) Backup

Answer 10

• routine copies of specific files chosen by user

-> files can be recovered

Question 11

Open Source

Answer 11

• used by anyone without license + distributed with source code

Question 12

Open Source Advantages

Answer 12

• can be modified + improved by anyone
• Tech support from online communities
• Sold on

Question 13

Open Source Disadvantages

Answer 13

• support may not be sufficient/incorrect
• lower security

Question 14

Closed source

Answer 14

• needs license –> user can’t access source code - company owns license

Question 15

Closed Source Advantages

Answer 15

• Thorough, regular updates
• company owning software provides support + user manuals
• Higher security

Question 16

Closed source disadvantages

Answer 16

• restricts how many can use software at once
• users can’t modify/ improve software

Question 17

Translators

Answer 17

• programs converting high level code into low-level code

Question 18

(T) Compiler

Answer 18

• conversion all at once after checks + reporting errors
• compiled code specific to certain devices/processor types + OS

Question 19

(T) Interpreter

Answer 19

• translation +execution line by line
• reports errors in line of codes
• faster, code instantly executed, slower than running compiled code
• more portable

Question 20

(T) Assembler

Answer 20

• translates assembly code to machine code ( 1 to 1 basis)

Question 21

(T) Assembly code

Answer 21

• low level language –> next level up from machine code

–> platform specific - dependent on instruction set of processor

Question 22

Stages of compilation

Answer 22

• when compiler is used, high level code turned into object code then ready to be used

lexical analysis - syntax analysis - semantic analysis - code generation - optimisation

Question 23

Lexical analysis (1)

Answer 23

• whitespace + comment removed

===============================================================

while flag = False;

print “not found”;

terminates when item is found

while flag = False:

print “not found”;

===============================================================

• remaining code analysed for keywords + names of variables + constants –> replaced with tokens + info about token stored in symbol table

Question 24

Syntax analysis (2)

Answer 24

• tokens analysed against grammar + rules of programming language
• any errors flagged as syntax errors + added to list of errors
• abstraction tree: represent source code in a tree

semantic analysis –> logical mistakes are deleted

Question 25

Code generation (3)

Answer 25

• abstract syntax tree used to produce machine code

Question 26

Optimisation (4)

Answer 26

• searches areas of code which could be more efficient
• aim: faster to execute
• stage can add to overall time taken for compilation
• redundant parts of code removed
• risk: excessive optimisation –> alter the way the program behaves

Question 27

Linkers

Answer 27

• piece of software responsible to link external modules + libraries used in code

Question 28

(L) static

Answer 28

• modules + libraries added directly into main file –> increase size of file
• any updates to modules + libraries externally won’t affect program –> specific version of library can be used

Question 29

(L) dynamic

Answer 29

• addresses of modules + libraries are included in files where they are referred
• when program runs, loaders retrieves program at specific address so it can be executed
• files remain small + external updates feed through main file -> no need to rewrite code

Question 30

Loaders

Answer 30

• program provided by OS
• when file executed. loader retrieves library/ subroutine from given memory location

Question 31

Libraries

Answer 31

A collection of pre-compiled routines which can be incorporated into a program like static/ dynamic linking

Question 32

Use of libraries

Answer 32

• ready to use, error free –> saving time
• developing/ testing modules - reused in multiple programs
• provide specialised functions
• popular libraries –> mathematical + graphical functions