Software and software development Flashcards
What is meant by the term ‘operating system’?
A collection of programs that work together to provide an interface between the computer and the user
Give examples of mobile phone operating systems
Android
iOS
Give examples of desktop operating systems
Windows
MacOS
Name the features that an operating system can provide for a computer system
- File management (moving, editing, deleting files and folders, sorting files into directories)
- Memory management (paging, segmentation, virtual memory)
- Resource management (schedulling)
- User Interface
- Security (firewalls
- Interrupt management
- Utility software (disk defragmentation, antivirus, backup…)
- Input/Output management (using device drivers)
What is meant by paging?
MEMORY MANAGEMENT OS
Memory is split into equally sized sections known as pages
-Programs are made up of a certain number of pages
-These pages can be swapped between main memory and the hard disk as they are needed
Explain memory management by the OS
Computer memory has to be shared fairly between the multiple programs and applications being used
-Often MM is not large enough
-So one of the roles of the OS is to make sure that main memory is shared efficiently through paging, segmentation and virtual memory
What is meant by segmentation?
MEMORY MANAGEMENT OS
Splitting up of memory into variable sized divisions known as segments (which vary in size)
-Segments are representative of structure and logical flow of program as each is allocated to blocks of code (eg. conditional statements or loops)
Segmentation is the process of splitting up memory into equally sized divisions called segments?
TRUE OR FALSE
FALSE
They dont necessarily have to be equal they are ‘logically sized’, which means that they are split depending on the logical structure of the program as each segment is allocated to a section of code
What is meant by virtual memory?
Refers to a memory management technique used by OSs to extend the apparent amount of available memory by using both the computer’s RAM (main memory) and a portion of secondary storage (such as a hard disk or SSD).
VM uses a section of the hard drive to act as RAM when there isnt enough space in MM.
So:
Sections of programs not being used currently are temporarily moved to VM through paging which frees up memory in RAM
Give a disadvantage of paging
Disk thrashing
When the disk freezes as a result of pages being swapped too frequently between main memory and the hard disk
-So more time is spent swapping rather than actually running the program
-This gets worst as virtual memory is filled up as:
In general the system has to swap pages in and out more frequently
VM must continually decide which pages to swap out to make space for others, this adds to overhead
Disk operations are slower than RAM operation
What is meant by RAM?
RANDOM ACCESS MEMORY
Type of computer memory that is used to temporarily store data that is being actively used or processed by the computer
-Volatile memory = it loses its contents when power is turned off
MAIN MEMORY
Split into 2 parts:
RAM= Random Access Memory
ROM = Read only Memory
What is meant by volatile memory?
Requires power in order to retain its contents
What is meant by the term ‘Random Access’ in RAM?
Data in RAM can be accessed in any order without the need to go through other data sequentially.
MEANS THAT it doesn’t need to start from the beginning and go through all previous data to reach a particular piece of data
-Allows for quick and efficient information retrieval
What is meant by the term interrupts?
Signals generated by software or hardware indicating to the processor that a process needs attention
What is taken into account before servicing interrupts?
Their priority / how urgent they are
Interrupts are ordered in a priority queue in a special register known as an interrupt register
Explain the role of the OS in Interrupts
The job of the OS is to ensure that interrupts are serviced fairly (taking into account their priority) by the processor through the Interrupt service routine (ISR)
Explain the Interrupt service routine
1.Processor checks contents of interrupt register at the end of each FDE cycle
- If interrupt exists of higher priority than the process being executed, current contents of the Special purpose registers in the CPU are temporarily transfered into a stack
3.Processor responds to interrupt by loading appropriate Interrupt Service Routine (ISR) into RAM
- A flag is set to signal the ISR has begun
- One ISR is serviced flag is reset, interrupt queue is checked again for interrupts of higher priority than one being executed.
- No more/ lower priority interrupts then contents of stack are placed back into Special PRs and the FDE cycle is resumed
What is disk thrashing?
The excessive swapping of pages between RAM (main memory) and hard disk (secondary storage)
Schedulling algorithms can be:….
Preempt = interrupt
Pre-emptive: If a new job arrives with a shorter remaining time than the currently running job, the CPU will preempt (interrupt) the current process and switch to the new, shorter task.
Non pre-emptive: Once a job starts executing, it cannot be interrupted by other processes. The CPU remains committed to that process until it completes.
What is meant by schedulling?
One of the roles of the OS is to ensure that all sections of program being run (jobs) receive a fair amount of processing time
-This is done by implementing schedulling algorithms (which can be preemtive or non preemptive)
Give examples of pre-emptive schedulling algorithms
-Round Robin
-Shortest Remaining Time
-Multilevel Feedback Queues
Give examples of non pre-emptive schedulling algorithms
-First come first served
-Shortest Job first
Give disadvantages of Round Robin
-Doesnt take into account job priority
-Longer jobs will take much longer to complete as their execution is inefficiently split into multiple cycles
Give an advantage of Round Robin
-Each job is seen to/ carried out
Explain the Round Robin schedulling algorithm
ITS PRE-EMPTIVE
-Jobs are stored in a queue with the first jobs in being the first out
- The first job in the queue gets its time slice. (Each job in queue is given a section of processor time (TIME SLICE) which it is allowed to execute within)
- Once the time slice expires (whether the job is finished or not), the job is paused and moved to the end of the queue.
- The next job in the queue gets its time slice.
- The process repeats for all jobs in the queue.
- If we get a job that has been finished its removed from the queue
Explain the First Come first serve schedulling algorithm
NON PRE-EMPTIVE
-Jobs are carried out in chonological order by which they entered the queue
(so essentially first come first serve…)
Give a disadvantage of the First Come first serve schedulling algorithm
Doesnt allocate processor time based on the priority of each job (as the jobs are carried out in chronological order)
Explain the multilevel feedback queues schedulling algorithm
PRE-EMPTIVE
Makes use of multiple queues, with each queue being assigned different priority levels
-Jobs are executed by the CPU starting from the highest-priority queue to the lowest priority queue, with each job in each queue using a time slice.
-If a job in a high-priority queue doesn’t finish within its time slice, it may be moved to a lower-priority queue and then given a larger time slice for its next turn.
Give an advantage of multilevel feedback queues schedulling algorithms
Takes into account the priorities of the jobs to be completed
Give an disadvantage of multilevel feedback queues schedulling algorithms
Difficult to implement due to the deciding of which job to prioritise based on the combination of priorities
What is meant by processor starvation?
When a process is delayed or unable to access the CPU, preventing it from executing.
*This situation arises when higher-priority tasks continually take precedence over lower-priority ones, resulting in certain tasks being “starved” of processing time.
-Disadvantage which can occur in Shortest Job first schedulling algorithms
Explain the Shortest Job First Schedulling algorithm
NON PRE-EMPTIVE
-Queue storing the jobs which need to be processed is ordered according the time they will take to be completed
-(Longest jobs at the end and shorter jobs are given preference)
Give disadvantages of using the Shortest Job First Schedulling algorithm
-Processor starvation (lower priority jobs dont end up getting done as higher priority/ shorter jobs keep getting added to queue)
-Requires processor to know how long each job takes which is not always possible
Explain the Shortest Remaining time schedulling algorithm
ITS PRE-EMPTIVE
The queue storing jobs to be processed is ordered based on the time each of them have remaining to be completed
(Jobs with less time remaining are prioritised and therefore at the start of queue)
If a new process arrives with a shorter remaining time than the currently running process, the CPU will preempt (interrupt) the current process and switch to the new, shorter task.
Shortest job first is a type of schedulling algorithm most suited for…
batch systems ( a type of OS where jobs or tasks are executed in groups or batches without interactive user input during execution)
Explain the difference between Shortest Job first and Shortest remaining time algorithms
Shortest Job First
Non preepmtive: Once a process starts executing, it cannot be interrupted by other processes. The CPU remains committed to that process until it completes.
It has a priority queue which prioritices the shortest jobs over the longer ones meaning that the shortest jobs will be completed first
Shortest Remaining Time
Preemptive: If a new process arrives with a shorter remaining time than the currently running process, the CPU will preempt (interrupt) the current process and switch to the new, shorter task.
The queue storing jobs to be processed is ordered based on the time each of them have remaining to be completed.
Give a disadvantage of Shortest remaining time schedulling algorithm
Risk of processor starvation for longer jobs if shorter jobs keep being added to the job queue
What are the different types of Operating Systems?
-Distributed
-Embedded
-Multi-Tasking
-Multi-User
-Real Time
There are various types of Operating Systems. Distributed is one of them.
What is meant by a distributed Operating System?
Its run accross multiple devices
Allows the load to spread accross multiple computer processors when running a task
There are various types of Operating Systems. Embedded is one of them.
What is meant by a embedded Operating System?
Designed to perform a small range of specific tasks
-Its catered towards a specific device
-Has limited functionality and they are hard to update
There are various types of Operating Systems. Multi-tasking is one of them.
What is meant by a Multi-tasking Operating System?
Allows user to carry out tasks seemingly simultaneously by using time slicing ( so it uses a pre-emptive schedulling method)
-To switch quickly between programs and applications in memory (so it creates the illusion that they are all ruining at once)
Each application or process is given a time slice to use the CPU for a brief period before the OS switches to another task.
There are various types of Operating Systems. Multi-User is one of them.
What is meant by a Multi-User Operating System?
Multiple users make use of one computer, typically a supercomputer.
A schedulling algorithm needs to be used so that processor time is shared fairly between jobs
There are various types of Operating Systems. Real Time is one of them.
What is meant by a Real Time Operating System?
Used in time critical computer systems
-As its designed to perform a task within a guranteed time frame
Which type of operating system consumes the least amount of power out of all the types?
Embedded
When would a Real Time OS be suitable?
For systems which manage situations where a response within a certain time period this can be crucial to safety (eg self driving cars)
*As they perform a task within a guaranteed time frame
What the BIOS? Explain it
BASIC INPUT OUTPUT SYSTEM
-This is the first program which is run when a computer system is switched on
-Program counter register points to the location of the BIOS when the computer is started up as the BIOS is responsable for doing checks before the OS is loaded into memory (RAM) from the hard disk
*IT IS ONLY AFTER THESE CHECKS THAT THE OS CAN BE LOADED INTO RAM FROM THE HARD DISK)
CHECKS:
-Poweron self test (POST) = ensures all hardware (disk drives, keyboard) are connected correctly and functional
Checks CPU clock, memory and processor
Checking for any external memory devices connected to the computer
What is meant by the term ‘bootstrap’?
The name of the program which loads the operating system from the hard disk into main memory (RAM)
The name of the program which loads the operating system from the hard disk into main memory (RAM) is?
Bootstrap
What are device drivers?
Computer programs which allow the OS to interact with hardware
E.g When a piece of hardware such as a keyboard is used, the device driver communicates this request to the OS
-The OS then produces a relevant output such as displaying a character on the screen
Device drivers interact with the OS. What is the kind of relationship between device drivers and the OS it interacts with?
Device drivers are specific to the operating system installed on the hardware device
Device driver’s are specific to a computer’s architecture
TRUE OR FALSE?
TRUE
Diff device drivers must be used for different device types (e.g smartphones, game consoles, desktop PCs)
What is a virtual machine?
A theoretical computer as it is a software implementation of a computer system
It also provides an environment with a translator for intermediate code to run
Using the example of the user typing in a character into their keyboard. How would the use of device drivers be relevant in dispkaying this on the screen?
A device driver is a program provided by the OS which allows the OS to communicate with hardware
When a piece of hardware such as a keyboard is used, the device driver communicates this request to the OS
-The OS then produces a relevant output such as displaying a character on the screen
What is meant by intermediate code?
Code that is halfway between machine code and object code
Its independent of processor architecture so it can be used across all different machines and operating systems
Give me an advantage of intermediate code
Its independent of processor architecture so it can be used across all different machines and operating systems.
This is because instead of being tied to a specific CPU design (harvard, vonN..), intermediate code targets a virtual machine
Give uses of Virtual machines
-Protection from malware
(as malware will affect the Virtual machine rather than the device being used as VMs operate in isolated environments)
-Running incompatible software
(Programs specific to diff OSs or diff versions to the host OS can be run within a VM instead as VMs are independent of computer architecture)
-Provides a development environment for programmers to test programs on diff OSs (as it saves money having to purchase different devices for testing)
Can you explain why Virtual machines can provide a device protection from malware?
Virtual machines operate in ISOLATED environments. Each VM runs its own operating system and applications independently from the host machine/device and other VMs.
This isolation helps contain malware, preventing them from spreading to the host system or affecting other VMs.
How does a virtual machine help when running incompatible software?
Programs specific to diff OSs or diff versions compared to the host OS can be run within a VM which saves money in having to purchase the required hardware
(e.g games console being implemented on a PC via a virtual machine)
Software can be categorised as…
-Application software
-Systems software
What is meant by application software?
Software designed to be used by the end user to perform one specific task
It requires systems software to run
Give examples of application softwares
-Word processing
-Spreadsheets
-Web browsers
-Desktop publishing
What is systems software?
Software designed to manage and control the hardware components of a computer, as well as provide a platform for running application software.
(So it serves as a bridge between the hardware and user applications)
Give examples of Systems software
-Operating systems
-Library programs
-Utility programs
-Device drivers
-Translator
What is meant by ‘utilities’?
A type of system software which is responsable for the consistent, high performance of the operating system
-Linked to the maintenance of the OS
Disk defragmentation is a type of utility software
Explain it
Disk defragmenter utility rearranges contents of hard disk so that files can be stored in contiguous spaces so they can be accessed faster
-As hard disk becomes full, R/W slow down
This is because files become fragmented as they are stored in diff parts of memory’
(fragmented = scattered)
Give examples of utilities
-Compression
-Disk defragmentation
-Antivirus
-Backup
-Automatic updating
Why does fragmentation occur?
When files are divided into multiple parts (fragments) and stored in different areas of the disk.
Occurs over time as files are created, deleted, and modified.
As files are deleted, small gaps are left on the disk. When new files are saved, they may be broken up and placed into these gaps if there isn’t enough contiguous space available, leading to fragmentation.
Antivirus is a type of utility software
Explain it
Responsible for detecting potential threats to the computer
Automatic updating is a type of utility software
Explain it
Ensures system is up to date ==> tackles security flaws, less vunreable to malware
Updates are automatically installed when the computer is restarted
Backup is a type of utility software
Explain it
Automatically creates routine copies (regularly scheduled backups) of specific files selected by user.
User also specifies how often these are backedup
Good for power failure, malicious attack so files can be recovered
What is meant by a ‘translator’?
A program classed as system software which converts high level source code into MC low level object code which is then ready to be executed by a computer
3 types: assembler, compiler, interpreter
What is the main role of a compiler?
Translates high level code into machine code
How does a compiler work?
Translates entire HL code into MC all at once and produces an executable file
-First checks for errors and reports back if found any
-Then translates whole code at once
-Produces machine code which can only be executed on certain devices
*Compiled code is specfic to a particular processor type and OS(meaning that its platform specific, so they are dependent on the instruction set of the processor(processor) and ensure compatibility with OS)
-Code can be run without need for source code or translator to be present because of the executable file
*If you need to make changes, after that the whole code needs to be recompiled
Assembly code is platform specific
What does this mean?
Instructions used are dependent on the instruction set of the processor as each processor may have a diff instruction set and must be compatible with the OS
Give info on assemblers
-They translate assembly code into machine code
-Each line of assembly code is equivalent to almost one line of machine code (one to one relationship)
-Platform specific as they convert assembly code into machine code, assembly code is tailored to a specific processor as diff processors have diff instruction sets and must be compatible with the target OS
Which translator has the longest initial compilation process and why?
Compilers as they carry out multiple checks to see if there are any errors
Interpreters
Translate HL code into MC line by line
-They stop and alerts there is an error if it detects one ==> Good for debugging as it stops when it gets to an error
-Slower than running compiled code as code must be translated each time its run/executed
-Both interpreter and source code must be present when code is run on different devices, however code can be executed on a range of diff platforms as long as right interpreter is available
Generally which runs faster a compiler or interpreter?
A compiler is generally faster
-A compiler translates the entire source code into machine code (or an intermediate language like bytecode) before the program is run.
This produces an executable file, which can then be executed directly by the hardware without needing the source code or the compiler.
-An interpreter translates the source code line by line while the program is running, and executes each line immediately after translating it.
This means that each line has to be translated every time the program is run, which slows down execution.
Interpreted code is generally more portable
TRUE OR FALSE?
Compiled code: Translates the entire source code into machine code and produces an executable file.
This executable file can run without the compiler or source code because the machine code is directly understood by the CPU.
If the compiler used is not compatible with a given platform, the executable cannot run there unless the code is recompiled for that specific platform.
However:
Interpreted code: Does not produce a standalone executable file.
Instead, it translates and executes the source code line-by-line or in blocks every time the code runs.
As long as the interpreter is compatible to the device/platform you’re using, the same code can run without needing any changes. The interpreter takes care of making the code work on different systems.
When a compiler is used, high level code goes through…. before…
STAGES OF COMPILATION
When a compiler is used, high level code goes through 4 STAGES before IT IS TURNED INTO OBJECT CODE READY TO BE EXECUTED
Stages:
Lexical Analysis
Syntax Analysis
Code Generation
Optimisation
STAGES OF COMPILATION
Lexical Analysis
- Lexical Analysis:
-Whitespace and comments are removed
-Remaining code is analysised for keywords and names of constants and variables
-which are replaced with tokens. Info about each token associated with each keyword or identifier is stored in a symbol table
STAGES OF COMPILATION
Syntax Analysis
- Syntax Analysis
-Tokens are analysed against rules of programming language, if they break these they are flagged up as syntax errors (incomplete brackets, undeclared variable type)
-An abstract syntax tree is produced
-Further details about identifiers is added to symbols table
-Semantic analysis is carried out (logic mistakes are detected)
Representation of source code in the form of a tree
What is this called?
Abstract syntax tree
What is meant by an ‘abstract syntax tree’?
A representation of source code in the form of a tree
What is meant by semantic analysis?
Analysing the code for logic errors such as undeclared identifiers, multiple declaration
Give examples of syntax errors
-Undeclared variable type
-Incomplete set of brackets
Give examples of semantic errors
-Undeclared identifier
-Multiple declaration
STAGES OF COMPILATION
Code generation
- Code Generation
The abstract syntaxt tree produced in the syntax analysis stage is used to produce machine code
STAGES OF COMPILATION
Optimisation
-Looks for sections of code that can be made more efficient
-Aim is to minimise the time taken for the code to execute by:
Redundant parts of code are removed and replaced by with more efficient ones or grouped together which produces the same result
STAGES OF COMPILATION
Optimisation
Give disadvantages of this
X Excessive optimisation may change the way the code behaves
X Adds to the overall time taken for compilation
What is meant by a linker?
Piece of software responsible for linking external modules and libraries included within the code
There are 2 types: Static and Dynamic
What is meant by a static linker?
A linker is a piece of software which links external modules and libraries included within the code
Static:
Modules and libraries are added directly to the program file (this increases size of file as the L and M are part of file).
Any updates made to libraries or modules externally will not affect the program meaning that you can use a specific version of a library
What is meant by a dynamic linker?
A linker is a piece of software which links external modules and libraries included within the code
Dynamic:
Addresses of libraries and modules are included in the program file where they are referenced at points where they are needed at runtime
-When program is run, the loader retrieves these using the specified addresses so program can be executed.
Give advantages of dynamic linkers
-External updates affect the main file so you dont need to rewrite the code (compared to static where any updates to the libraries or modules won’t affect the code)
-File size remains small as addresses to libraries and modules are included in the file rather than the modules and libraries themselves. (so M and L can be retrived when code is run by a loader at the specific addresses when program is run)
What is meant by a loader?
Programs provided by the OS
In static linking: At runtime, the loader loads the complete executable (including the code and library/modules) into memory.
In dynamic linking: Loader loads the program into memory.
Then retrieves and loads the library or module from the specified memory location
What is a library?
Pre compiled, pretested programs which can be incorporated within other programs using either static or dynamic linking
Give advantages of using libraries
-They are ready to use and error free as they are precompiled and pretested ==> so saves time developing and testing
-Can be reused within multiple programs
-Often provide a specialised range of already programmed functions which would otherwise require a lot of time and effort to develop (e.g a dijkstra’s algorithm)
Give the common stages of a software development life cycle (SDLCs)
-Analysis
-Design
-Development
-Testing
-Implementation
-Evaluation
-Maintenance
SOFTWARE DEVELOPMENT LIFE CYCLE
Explain what happens in the analysis stage
Stakeholders state what they require from finished product
-Info is used to refine problem to be solved and system requirements
-Analysing advanatages and disadvantages of ways the problem is currently being solved
SOFTWARE DEVELOPMENT LIFE CYCLE
Explain what happens in the design stage
-Inputs, outputs
-User interface (eg menu, navigation)
-Hardware setup (eg. compatibility)
-Security features (eg. access levels)
-Test plan may also be developed at this stage
SOFTWARE DEVELOPMENT LIFE CYCLE
Explain what happens in the development stage
Design from ‘design’ stage is used to split the project up into individual, selfcontained modules which are allocated to teams for programming (decomposition)
SOFTWARE DEVELOPMENT LIFE CYCLE
Explain what happens in the testing stage
Program is tested against the test plan made in the design stage
By using:
-Alpha
-Beta
-White box
-Black box testing
SOFTWARE DEVELOPMENT LIFE CYCLE
Explain what happens in the implementation stage
Once changes have been made using the feedback from testing, software is installed onto users’ systems
SOFTWARE DEVELOPMENT LIFE CYCLE
Explain what happens in the evaluation stage
Evaluates the effectiveness of the software compared to the system requierements outlined in the analysis stage
Other criteria outlined: robustness, reliability, portability
SOFTWARE DEVELOPMENT LIFE CYCLE
Explain what happens in the maintenance stage
Any errors or improvements are flagged up by end users
Developers carry out frequent software updates to fix any bugs/security issues
Explain alpha testing
SOFTWARE DEVELOPMENT LIFE CYCLE
(IN TESTING STAGE) INITIAL BUGS
Carried out by the software development teams within the company which pinpoint bugs and fix them
(this is done before any external users sees it)
Explain beta testing
SOFTWARE DEVELOPMENT LIFE CYCLE
(IN TESTING STAGE) USER FEEDBACK
Software is released to a group of external users (who arent part of development) to gather user feedback and identify any remaining bugs or usability issues. (so real world feedback from users)
THIS IS DONE AFTER ALPHA TESTING
-This feedback from users is used to inform the next stage of development
Explain white box testing in the SDLC
SOFTWARE DEVELOPMENT LIFE CYCLE
(IN TESTING STAGE) LOGIC
*Focused more on the internal workings (code paths) compared to black box
to make sure the logic that behind each path of the code is what was expected
-Carried out by software development teams
-Using the test plan (which is based on the internal structure of the program) all possible routes through the program are tested
Explain black box testing in the SDLC
SOFTWARE DEVELOPMENT LIFE CYCLE
(IN TESTING STAGE) FUNCTIONALITY
*Focused more on external workings (inputs and outputs) compared to white box
-Software is tested about functionality without the people testing it being aware of the internal structure of the software (unlike white box testing)
-Carried out by end users (unlike white testing as its only the company’s development teams)
-The test plan traces through the inputs and outputs within the software
WATERFALL LIFECYCLE
The analysis stage includes a feasibility study which designers evaluate the feasibility of the project using…
TELOS
-Technical: is project possible considering the tech available?
-Economic: can problem be financed in the short term and long term?
-Legal: can the project be solved within the law?
-Operational: can the problem be successflly be implemented and mantained?
-Schedulling: can it be completed given the time available?
Give examples of programming methodologies
-Waterfall
-Agile
-Extreme programming
-Spiral
-Rapid application development
If a change needs to be made within the project being developed using the waterfall model….
Programmers must revisit all levels between the current stage and at the stage at which a change is to be made
X Makes model inflexible and not suitable for projects with changing requirements
X Users have very little input as they are only involved at the analysis and evaluation stages (start and end)
Name the stages in the waterfall lifecycle
Its being replaced with better models
- Analysis
- Design
- Implementation
- Evaluation
- Maintenance
Stages are completed in sequence from start to finish
A disadvantage for the waterfall lifecycle software methodology is that:
It makes model inflexible and not suitable for projects with changing requirements
Why is that?
If a change is being made:
Programmers must revisit all levels between the current stage and at the stage at which a change is to be made
Agile methodologies
A collection of methodologies which aim to improve the flexibility of software development and adapt to changes in user requirements faster
-So its easier to make changes and improvements
Less focus on documentation more focus on user satisfaction
-Problem is broken down into sections which are DEVELOPED IN PARALLEL
(deisgn and analysis phases often occur together)
Start: Analysis
Design prototype, build prototype, user feedback, refine prototype (repeat)
Finish: Final product
With agile methodologies less focus is given to.. and more focus is given to…
Less focus on documentation more focus on user satisfaction
This is because of the iterative nature of development so its also harder to produce high quality documentation
Agile methodologies prototype
-Prototype is delivered early and is built and improved in an iterative manner (built, reviewed, and improved upon repeatedly through cycles) so that new prototypes can be delivered throughout the development cycle
Extreme programming
This is an agile model in which the development team consists of a pair of programmers and their end user
-So must have good communication
-One may code the other will critique
Each iteration generates a ‘working version’ which means that it could function as the final product
Extreme programming is an agile model in which the development team consists of a pair of programmers and their end user.
The model is built on ‘user stories’. What does this mean?
System requirements are specified by the end user and used when designing the program
SOFTWARE METHODOLOGIES
Spiral model
Focus on managing risk-heavy projects
4 key stages:
-Analysis of system requirements
-Pinpointing and mitigating risks
-Development, testing, implementation
-Evaluating to inform next iteration
If project is found too risky at any point, it is terminated
Give a disadvantage of using the spiral model
Hiring risk assessors to analyse the risks involved can be EXPENSIVE
-So this methodology is only a good investment for large scale projects
SOFTWARE METHODOLOGIES
Rapid Application development
Instead of completing the entire project in one go, RAD focuses on developing prototypes or small working versions of the application. These prototypes are then presented to the users for feedback.
User requirements are gathered using focus groups
-Good for when user requirements are incomplete or unclear at the start.
In what situation would you use the Rapid Application development software methodology?
Used in situations where user requirements are incomplete or unclear at the start.
This is because first, an incomplete solution is developed and based on user feedback, another improved prototype is made
==> So this continues until the prototype matches the requirements of the end user (where it becomes the final product)
THE RAPID APPLICATION DEVELOPMENT SOFTWARE METHODOLOGY
Is used in situations where user requirements are incomplete or unclear at the start.
Give a disadvantage of this
Inefficient to work with as requirements change over the course of the project
(as you are constantly making changes which might get undone later)
What is meant by an algorithm?
A set of instructions to solve a problem
Give key qualities of an algorithm
-Must terminate/ reach a stopping condition
-Must deal with invalid inputs
-Well-documented for reference
-Well-commented so modifications can be made easily in the future (as it could explain what each part of the code does)
-Inputs must be clearly defined (what is valid and what is invalid as an input)
-For any defined input a valid output must always be produced
What is meant by a ‘feasibility study’?
Feasible= solution is practical and achievable.
A feasibility study is conducted early in the project to determine if the project is worth pursuing and if it can be completed successfully. (e.g. in the analysis stage of waterfall lifecycle)
Give an advantage of using waterfall programming methodology
-Clearly documented
Give an advantage of using agile programming methodology
-Produces high quality code (eg. working prototype is developed early and then constantly improved)
-Flexible to changing requirements
-Constant prototypes being produced
-Constant improvement due to iterative manner of building prototypes
-Allows for user feedback/input (thus more tailored to users’ needs/wants)
Give an advantage of using extreme programming methodology
-Produces high quality code (as one partner can code the other can critique)
-Constant improvement due to iterative manner of building prototypes/working version ==>-Constant prototypes being produced
-Flexible to changing requirements of end users
Give an advantage of using spiral programming methodology
-Thorough risk analysis and mitigation
-Constant prototypes being produced
Give an disadvantage of using waterfall programming methodology
-Lack of flexibility to make changes as if a change wants to be made them programmers must also revisit all the other levels between the current stage and the one that needs to be changed
==> so harder to make improvement based on user feedback
-No risk analysis (eg. such as in the spiral model)
Extreme programming, Spiral model and Rapid Application development are examples of…..
Agile methodologies
Because of the iterative aspect where is creates a prototype shares it with user and based on feedback it improves it
Give me disadvantages of agile methodologies
-Can led to poor documentation (as there is not much focus on it. Its also harder as there are so many prototypes to documenent and its hard to do this in depth)
-Constant interaction with user
Give disadvantages of using extreme programming
-Higher cost as you have 2 people working on 1 project at a time
-Good communication/teamwork is important between the 2 programmers
-Have to have constant interaction with user
-Developing constant prototypes may be costly (but may also be worth it for improvement)
Give disadvantages of using the spiral model
-Expensive to hire risk assessors
-Less focus on code efficiency
-High cost of constant prototyping
Give advantages of rapid application development
-Caters to users’ changing requirements as it uses a partially functioning prototype and builds upon it
-Produces prototypes throughout
Give disadvantages of rapid application development
-Poorer quality documentation (e.g loads of prototypes so its hard to document all. Also user requirements may change constantly so hard to maintain uptodate documentation)
Uses of the Agile methodology
Small to medium projects with some unclear requirements
(as you can keep building on from an initial prototype)
Uses of the Waterfall methodology
-Low risk projects
-Projects with little user input
-Static requirements (doesnt change in terms of requirements)
eg. Piece of general purpose software
Uses of the Extreme Programming (XP) methodology
Small to medium projects with some unclear requirements
(as you can keep building on from an initial prototype)
Uses of the Spiral model methodology
-Large projects (as its expensive due to all the risk accession) -Projects with a high budget
-Risk intensive projects
(eg. self driving car)
Uses of the Rapid Application Development methodology
-Small to medium project
-Low budget
-Frequent change in user requirements
-Short time frames
What is meant by a programming paradigm?
Different approaches to using a programming language
They are divided into imperative and declarative
Give examples of imperative programming paradigms
-Procedural
-Object oriented
Give examples of declarative programming paradigms
-Functional
-Logic
What is meant by an imperative programming paradigm?
Uses code that clearly specifies the actions to be performed
Procedural programming
Type of imperative programming
-Problem is broken into a sequence of procedures
-It emphasizes a logical flow of instructions that tell the computer what to do in a specific order
examples: Pascal, Python
Give examples of procedural programming languages
-Pascal
-Python
Object oriented programming
-Built on entities called objects formed from classes which have certain attributes and methods
-Useful for problems which have loads of reusable and similar characteristics
Give examples Object oriented programming languages
Python
Delphi
Java
What is meant by a declarative programming paradigm?
States the desired result rather than the series of instructions to get to the result
-Its the role of the programming language to determine how its best to get the result:
- Programmer describes the goal or outcome, and the underlying system or language takes care of finding the best way to achieve that goal.
(Used in: eg. AI, expert systems)
Give examples of functional programming languages
Haskell
Java
C#
Functional programming
DECLARATIVE PARADIGM
The concept of reusing a set of functions which form the main parts of a program
Logic programming languages
DECLARATIVE PARADIGM
-Uses code which defines a set of facts and rules based on a problem (rather than dealing with the step by step rules to solve these)
-Queries are used to find answers to these problems (so programmer defines what solution should look like and system figures out how to reach a solution)
Give an example of a logic programming language
Prolog
What is meant by ‘structured programming’?
A subsection of procedural programming in which the control flow (order its run) is given by:
-Sequence
-Selection
-Iteration
-Recursion
What is meant by ‘control flow’?
Control flow refers to the order in which individual instructions, statements, or functions are executed in a program.
What is meant by recursion?
When a subroutine calls itself until the base case is reached, which then terminates the recursion
What is meant by the ‘base case’?
In recursion, its a condition that prevents the function from calling itself and doesnt require recursion to produce an output
Define Iteration
A block of code is exectuted a certain number of times or while a condition is true
Define Selection
A block of code is run if a specific condition is met
Assembly language
-Uses mnemonics rather than binary (so its more compact)
-Each mnemonic is represented by a numeric code (which represents the machine level instruction understood by the processor)
-Its processor-specific ==> directly manipulates the processor, so good for embedded systems
-Easier for humans to understand
-Converted to MC using an assembler
One line of Assembly language is equivalent to one line of machine code
Assembly language is good for embedded systems
Why?
The commands that assembly language uses are processor specific as they directly interact with the CPU’s special purpose registers. These registers are used to interact with specific hardware components.
-Therefore, this allows a direct interaction with the hardware
Assembly language is processor specific.
What does this mean?
Processor-specific means that Assembly code is designed to work with a specific type of processor because the mnemonics and machine codes differ between processors as diff processors have diff instruction sets
(A program written in Assembly for one processor won’t work on a different processor without modification)
Explain what makes up a machine code instruction
2 parts
-Opcode= Specifies the instruction to be performed (eg. ADD)
-Operand= Value which relates to the data on which the instruction is to be performed
What is ‘opcode’?
A part of a machine code instruction which specifies the instruction to be performed
What is ‘operand’?
A part of a machine code intruction
A value which relates to the data which the operation is to be performed on
The addressing mode is part of the operand
TRUE OR FALSE?
FALSE
It is part of the opcode (specifies the instruction to be performed)
Addressing modes allow for a much greater number of locations for data to be stored
Why?
Because otherwise if they werent used the size of the operand would constraint the number of addresses
Therefore, instructions can refer to data in other ways, such as through indirect addressing or indexed addressing, which enables access to larger memory regions
What is meant by ‘intermediate code’?
Code that is halfway between machine code and object code
Makes programs portable= Its independent of the processor architecture so it can be used accross different machines and operating systems
(e.g bytecode)
Give a disadvantage of running intermediate code in a virtual machine
Can be slower rather than running it on the device it was designed for
Virtual machines can be used to create a development environment for programmers
Give an advantage of this
So that programmers can test programs on different operating systems.
Therefore, it saves time and money of having to purchase multiple devices just for testing
Intermediate code is independent of…
Its independent of the processor architecture so it can be used accross different machines and operating systems
Why would using a Virtual machine be good for SAFE testing and development?
A VM runs in an isolated environment separate from the host operating system.
This isolation ensures that any issues, crashes, or errors occurring within the VM do not affect the host system.
So can experiment freely with code, test risky changes without impacting their main operating system.
Virtual Machines enable you to run various ……. on the same ……
Virtual Machines enable you to run various operating systems (like Windows, Linux, or macOS) on the same physical device (host machine)
VIRTUAL MACHINES
Host machine refers to …
Host machine refers to the physical device
Application software depends on the system software to function
Why is that?
The application software needs the operating system (provided from system software) to allocate resources, manage files and facilitate communication with hardware.
System software provides an environment that allows the applications to run.
What is meant by source code?
Human-readable set of instructions and statements written by a programmer using a programming language.
(it must be translated into machine code by a compiler or interpreter to be executed by a computer)
What is object code?
The machine-readable code generated by a compiler or assembler after translating the human-readable source code.
Assembly language doesn’t count as source code
TRUE OR FALSE
FALSE
Source code does apply to assembly language. Assembly language code is considered source code because it is written in a human-readable form (using mnemonics) and must be translated by an assembler into machine code (object code) for the computer to execute it.
Does an interpreter generate object code?
No, it directly translates and executes source code line by line at runtime, without creating a separate, intermediate machine code file.
Can you explain why the code that is compiled doesn’t require the compiler to be run again?
A compiler translates the entire program into machine code or intermediate code first and creates a separate file (like an executable), which can be run without the need for the compiler to be involved again.
Bytecode is an example of a…
Intermediate language
Source code is written by a programmer and refers to object code before…
it has been compiled
When software is described as ‘open source’ or ‘closed source’, it refers to…
whether or not the source code is accessible to the public
What is meant by ‘open source’ code?
Code which can be used by anyone without a license and is distributed for anyone to use and modify.
What is meant by ‘close source’ code?
Code which requires user to hold an appropriate license to use software
Users cant access original source code as the company owns the copyright
What is the difference between open source and closed source code when it comes to the access rights of the code?
Open source= anyone can access the original source code even if they dont have a license
Closed= user needs a license to access it, as this code’s copyright license by the company that owns it
Give advantages of using open source for software
-Can be modified and improved by anyone
-Can be modified and sold on
Give disadvantages of using open source for software
-Modifications made by people may be incorrect
-Lower security as code may not be developed in a controlled environment
-No user manuals, relies on support from public (eg. online forums) this may be insufficient or incorrect
Give disadvantages of using closed source for software
-License restricts how many people can use the software at a time
-Users cant modifiy and improve software themselves
-Cost of paying to put a license (as the company)
Give advantages of using closed source for software
-High security levels as the software is developed professionally
-Company owning the software can provide expert support and user manuals
-Software can be regularly updated by the company who owns it
What is immediate addressing?
Operand is the actual value upon which the instruction is to be performed on
What is direct addressing?
Operand gives the address which holds the value upon which the instruction is to be performed on
What is indirect addressing?
Operand gives the address of a register which holds another address where the data is located
What is indexed addressing?
An index register is used which stores an offset.
The effective address of the operand is determined by adding the base address to the value in the index register
What is meant by instantiation?
The process of creating an object from a class
(e.g From class animal. cat, dog… are instances of the class animal)
Define ‘object’ in OOP
A particular instance of a class
Object Oriented Language
Class is a template for an object which defines the state and behaviour of the object
State= attributes = object’s properties/characteristics
Behaviour= defined by methods in class = define actions object can perform
OOP
Setter vs Getter
Setter = a method that sets out the value of a particular attribute
Getter= a method that retrieves the value of a given attribute
Why are getters and setters useful in OOP?
They help protect the integrity of an object’s state by controlling how its data is accessed and modified.
Instead of allowing users to directly accessing or modifying the object’s attributes, you use methods (getters and setters), which provide a layer of control over how the data is handled.
OOP
What is encapsulation?
The concept of bundling attributes and methods that operate on data into a single unit, known as a class.
Protects data integrity as it ensures that data remains secure and is not accidentally modified or misused by restricting access to them using access modifiers (e.g., public, private)
(so if attributes are declared as private then they can only be altered using public methods)
Why would you set the access modifier of an attribute as private?
Ensures that data remains secure and is not accidentally modified or misused
As this hiddes the attribute to protect the internal state of an object
What is meant by access modifiers?
Access modifiers are keywords used in object-oriented programming to define how accessible certain parts of a class (such as its attributes and methods) are from outside the class.
Public access modifier
Attributes and methods marked as public are accessible from anywhere in the program, including from outside the class.
Private access modifier
Attributes and methods marked as private are accessible only within the class where they are defined and are hidden from outside the class.
Protected access modifier
Attributes and methods marked as protected are accessible only within the class itself and by subclasses (e.g derived classes) but not by outside code.
Subclass=
Parent Class=
Subclass= Derived class
Parent class= Superclass
Give an advantage of inheritance
Because the derived class will have the same properties and methods as the parent class as well as some of its own
==> This allows programmers to reuse certain methods and properties of a class whilst also making some changes
Overriding and overloading are types of….
Polymorphism
What is meant by polymorphism?
Objects can behave differently depending on their class which can result in the same method producing different outputs
What is meant by ‘overriding’?
Its a type of polymorphism
Redefining a method within a subclass and altering the code so that it functions differently and produces a different output to the method in the superclass
(same name diff implementation)
(e.g in the class Shape. there are different shape objects such as square and circle. in the method ‘getArea’ the way that you would work out the area of a square and circle is different)
What is meant by ‘overloading’?
Its a type of polymorphism
When methods in the superclass have the same name but pass in different parameters
Give advantages of Object Oriented Programming
-Allows high reusability of code ==> so its useful for projects with similar properties
(inheritance and polymorphism allows this)
-Can have multiple programmers working on the code together at a time as each class can be developed independently of the other classes
-As OOP requires advanced planning to determine how the problem will be broken down into classes and how these will link eachother ==> good design plan can produce a higher quality software with less vunreabilities
-Has a modular structure so its easier to modify and update
-Clear to understand: Has a high level of abstraction ==> so programmers dont need to know about how the code is implemented (they just know what its purpose is)
(e.g dijkstra’s algorithm: programmer doesnt need to know how to program one rather just that the method is about that)
Give disadvantages of Object Oriented Programming
-Not really suitable for small problems where few components are reused, OOP may result in longer and inefficient program
-Requires an alternative thinking style as its a diff style of program (might be harder for those who are used to other paradigms/might be beginners/only used to procedural programming)
==> OOP concepts like inheritance, polymorphism, and encapsulation challenging for beginners to understand
-Code harder to follow and understand because as the size of the problem increases it leads to more complex program design
-Objects and classes often use more memory than procedural programming constructs, as each instance of a class requires its own memory for its attributes
-The use of abstraction, encapsulation, and polymorphism can result in more memory and processing overhead
Objects and classes (in OOP) often use more memory than procedural programming constructs
Why is that?
Objects and classes often use more memory than procedural programming constructs, as each instance of a class (each object) requires its own memory for its attributes
Why is the Round Robin algorithm considered preemptive?
Round Robin scheduling is considered preemptive because the CPU is forcibly taken away from a process after its time slice is over, even if the process hasn’t finished its task.
(it might be misleading as the algorithm orders the tasks in a queue with the tasks that came first at the front of the queue rather than in terms of priority)
SCHEDULING ALGORITHMS
Multilevel Feedback queue
If a job in a lower-priority queue has been running for a long time without finishing what may happen to it?
Job Promotion and Demotion:
It may eventually be promoted to a higher-priority queue to ensure that it doesn’t get stuck at the bottom of the queue for too long.
Why would Shortest Remaining Time be classed as a preemptive schedulling algorithm?
ITS PRE-EMPTIVE
The queue storing jobs to be processed is ordered based on the time each of them have remaining to be completed
(Jobs with less time remaining are prioritised and therefore at the start of queue)
If a new process arrives with a shorter remaining time than the currently running process, the CPU will preempt (interrupt) the current process and switch to the new, shorter task.
BASIC INPUT OUTPUT SYSTEM (BIOS)
-This is the first program which is run when a computer system is switched on
-Program counter register points to the location of the BIOS when the computer is started up as the BIOS is responsable for doing checks before the OS is loaded into memory (RAM) from the hard disk
What are the ‘checks’ that the BIOS does?
CHECKS:
-Power on self test (POST) = ensures all hardware (disk drives, keyboard) are connected correctly and functional
-Checks CPU clock, memory and processor
-Checking for any external memory devices connected to the computer
Explain how device drivers would work when a user enters something on a keyboard
E.g When a piece of hardware such as a keyboard is used, the device driver communicates this request to the OS
-The OS then produces a relevant output such as displaying a character on the screen
Compiler vs Interpreter Portability comparison (simple)
Portability Comparison
Compiled code:
Less portable because the machine code is tied to a specific platform.
If you want to run the program on a different platform, you need to recompile the source code using a compiler that supports that platform.
Interpreted code:
More portable because the source code doesn’t need to be modified for different platforms.
You only need to ensure a compatible interpreter is available for the target platform.
What is the difference between semantic errors and syntax errors?
Syntax errors: Prevent the code from running because it breaks the language’s rules.
Semantic errors: Let the code run but lead to unexpected or incorrect behavior due to a logical issue.
Software development life cycle
White box testing is carried out by people outside the company
TRUE OR FALSE?
FALSE
-Carried out by BOTH company and end users (unlike black box testing as its only the company’s development teams)
Who carries out black box testing?
Black: end-users, external testers
Who carries out beta testing?
Carried out by endusers/ external users after alpha testing has been done
Who carries out alpha testing?
Carried out by the software development teams within the company
(after this beta testing is performed)
Who tests in each?
Alpha testing
Beta testing
White box testing
Black box testing
Black: end-users, external testers
White: Internal development team
Alpha: Internal development team
Beta: External users, public testers
Advantages of object oriented programming
-Useful for problems which have loads of reusable and similar characteristics
-Also focuses on making programs easy to update and maintain (as similar characteristics are grouped together in classes)
Its a type of polymorphism
When methods in the superclass have the same name but pass in different parameters
Overloading
Describe differences between Waterfall and Spiral Models
- spiral works on a small set of requirements…
- …waterfall starts with all requirements
- spiral repeats from the start of the cycle each iteration…
- …waterfall to repeat needs to reverse through previous stages first (so it doesnt iterate it just creates the program step by step)
- Spiral focuses on risk mitigation…
- … Waterfall focuses on the delivery of the project as a
whole.
Why may Text Editors be better to work with than IDEs?
May be better when learning to program as it
forces the user to type everything in full / doesn’t
give suggestions, helping things stick in
memory.
Give advantages and disadvanatges of using local variables
- Increases data integrity
- More efficient memory usage as its removed from memory once subroutine is terminated
- Stops other subroutines accidently altering variable
1 mark for drawback
e.g. - Cannot be accessed directly by other subroutines
- It has to be passed into a subroutine as a parameter
Advantage of using disk defragmentation utility
Disk Defragmentation…
* …To keep optimal r/w speed for a Hard disk drive
Cost of open source vs closed source
Cost
Open Source
* (generally) free to use
* May have to purchase maintenance
contracts
Closed Source
* (sometimes) have to pay to license the
software
* If paid will (usually) it will come with some
level of support
Usability/extensibility of open source vs closed source
Usability/extensibility
Open Source
* Tends to have a lower focus on user interface (may be harder to use)
* Source code released (under license)
* Source can be edited
* Can be redistributed (under license)
-Because you can edit you can add more specialised functionality to the code to tailor your own needs
Closed Source
* Professionally developed so more focus on user interface
* Software is distributed with a restrictive license by company
* Only executable/object code is
distributed//source code not distributed
* Cannot be redistributed (as its owned by the company)
-Code cant be edited so you cant add aditional functionaloty
Security of open source vs closed source
Security
Open Source
* Many of the contributors may not be
professional (potentially massive bank of volunteer
developers working on the product)
* Code available to be edited by
anyone even people with
malicious intentions
Closed Source
* Closed teams of developers
* security fixes usually addressed quicker
-Good to have high security measures if its for a company that is using this as bad security have bad reputation on the company
Support of open source vs closed source
Support Available
Open Source
* Source code released (under license) (so you can see it)
* Open communities mean lots of support
options could be available (but most are probably not professionals)
Closed Source
* User manuals and specialist support
Overall evaluation for open source vs closed source for a business looking to use either
Open source (less costs but need to support yourself)
would lead to potential cost savings if looked to self support by using online communities or handling the code themselves.
Closed Source *(more support)
If Charlie lacked technical skills, the better user interface design from professional developers may be better
Tighter security (good for a business)
Define the term register
-Small, fast piece of memory/used for temporarily storing data (1)
-Within the processor (1)
Give an advantage of increasing the amount of RAM in a computer
More programs can be open simultaneously without the need to use much slower virtual memory.
