Ocr Computer Science 2.1 - 2.2

Front 1

What is abstraction ?

Back 1

The removal of unnecessary detail, leaving only what is essential remaining.

Front 2

Why is abstraction needed ?

Back 2

- Abstraction is required to enable complex procedures or events to be modeled.

- Computer programs cannot account for every single element of an event as this would be extremely complex and time consuming.

Front 3

What is abstraction used for in computer science?

Back 3

- To represent real world objects in a way which can be processed.

- Creating algorithms (removing the unnecessary)

- Modelling

- Encapsulate (object oriented programming)

- Layering (OSI model, TCP stack etc)

Front 4

What research steps should be conducted BEFORE a project begins ?

Back 4

- What do current systems do ?

- How do they work (exactly) ?

- What is needed ?

- What resources do you need to make a new system ?

- How will you work efficiently ?

Front 5

What is caching ?

Back 5

Caching is the idea keeping a local store of data to speed up a process.

Front 6

What might the cache contain ?

Back 6

- Frequently used data.

- Frequently used instructions.

- Data that a system has predicted it will need next (pre-fetching).

Front 7

What scenarios may a cache be used ?

Back 7

- Storing instructions and data in a CPU

- In a database system

- On a proxy server in a network

- By large website hosts and ISP's

Front 8

Advantages of caching

Back 8

- Caching will significantly increase system performance as data is available locally, almost immediately.

- Saves waiting for long read/write operations.

- Prevents repeated read/write, fetch/store operations.

- Can reduce bandwidth/network usage.

Front 9

Disadvantages of caching

Back 9

- Difficult to code prediction routines

- Can be very complex to set up, especially in database systems.

- Can cause synchronization issues

- If there's a cache 'miss' (a branch unexpectedly happens in code or similar) then the whole cache must be flushed and refilled causing a stall in performance.

Front 10

Forms reusable code comes in

Back 10

- Libraries

- Classes

- DLL's (Dynamic Link Libraries)

Front 11

What might existing libraries cater for ?

Back 11

- Drawing and handling the user interface

- File load and save

- Memory management

- Mathematical functions

- Input and output operations

- Graphics

Front 12

What is a procedure ?

Back 12

- A block of code which performs a specific task or sub-task.

- It may allow data to be sent in and may give data out again when complete.

- It is re-usable.

- It can be called from anywhere in your code.

Front 13

What does Thinking procedurally entail ?

Back 13

- Break a problem down into chunks.

- Decide which could be a re-usable block of code.

- Work out what inputs the procedure will need to do the task.

- Work out what outputs the procedure should produce.

- Make those procedures.

Front 14

Method for breaking down a program

Back 14

- Decompose the program - what are the main tasks this program should do.

- Abstract - make sure you are only focusing on what is strictly necessary to complete the task.

- Decide what variables your program will need.

- Algorithms - what will your code need to calculate/manipulate/produce.

-Outline algorithms - what will the basic structure of your code be.

- Decide what procedures you should produce.

Front 15

What is the process of thinking logically

Back 15

- Identify a problem

- Break it down (decomposition)

- Removing unnecessary complications and focusing on the true problem (abstraction)

- Identifying concurrency, algorithms, efficiency saving, etc

- Designing the solution

Front 16

Rules to follow to solve a problem

Back 16

- What are the steps that must be taken?

- In what order?

- What is the eventual goal?

- What decision must be made?

Front 17

What is concurrency

Back 17

Concurrency is the idea of doing multiple things at the same time.

Front 18

What else does concurrency apply to?

Back 18

- Modelling projects

- Suggesting time savings in existing processes

- Managing human resources

Front 19

Benefits of Concurrency

Back 19

. Faster processing - More things can happen during the same time window.

. Energy efficiencies - As more is being done each cycle, less time us used processing, so less energy is used.

. Efficient use of resources - Less idle processor time, more time available for other tasks.

- Less apparently lag when running a program.

Front 20

Trade-offs of concurrency

Back 20

. Increased complexity - Programs must be specifically designed to work concurrently (threading)

- Compilers need to be able to explicitly target multi-core architectures.

. Not suitable for tasks - It is not possible to make all problems concurrent

. Does not provide a doubling of speed - Some tasks may be more/less concurrent than others.

-Some threads may have to wait for the outcome of others to proceed.

Front 21

Sequence

Back 21

Code is executed sequentially - meaning that statements and functions are run one-after-the-other.

Front 22

What is branching

Back 22

Branching is where code splits. The programme is interrupted and control is moved to another part of the programme.

Front 23

Reasons for interrupting a programme

Back 23

- Decisions to be made based on data

- Different outcomes

Front 24

Three loops for iteration

Back 24

Do until

While

For

Front 25

What is iteration

Back 25

Iteration is a combination of branching and sequencing to repeat statements and functions in programmes

Front 26

Do until description

Back 26

This will loop part of your code until something happens- these will run at least once before reacting to the conditions that are set.

Front 27

While description

Back 27

This loop will repeat until something changes. It differs from until by checking the criteria before starting the loop.

Front 28

For description

Back 28

This loop repeats a fixed number of times, either you tell it how many times to loop or they will figure this out from another part of the programme.

Front 29

What is recursion

Back 29

Recursion is when a procedure calls itself.

Front 30

Positives of recursion

Back 30

- Can be easier to read and write recursive code

- Recursion often creates a more sensible/natural solution - no leaving/re-entering a procedure repeatedly in one go.

- Some tasks are just naturally recursive.

Front 31

Negatives of recursion

Back 31

- Recursion requires more memory.

- Recursion is difficult to race as each call has its own set of variables.

- It is possible to run out of memory if too many calls occur.

Front 32

Implications of using global variables

Back 32

- Global variables are more likely to be altered or changed by accident later on in the programme causing unexpected results.

- When global's are used in excess, memory problems arise as they are kept in memory constantly even when not in use eating up memory.

- Excess use of global's makes for messy code.

Front 33

Important definitions for IDEs

Back 33

The code that is written in an IDE is refereed to as Source code.

The process of writing, testing, debugging, packaging, documenting, etc is refereed to as the build.

Front 34

Run-time environments

Back 34

Software to support the execution and running of programs. It allows the developer to run their code during development in order to check for logical errors.

Front 35

Memory inspector

Back 35

A facilitywhich will display the contents of a section of memoryt

Front 36

Error diagnostics

Back 36

Usedwhen a program fails to compile or to run. Error messages are displayed to help the programmer diagnose what hasgone wrong

Front 37

Code editor

Back 37

Allows a programmer to enter, format and edit source code

Front 38

Compilers

Back 38

Convertssource code into executable machine code. Once compiled, a program can be run at any time

Front 39

Interpreter

Back 39

Convertseach line of source code into machine code, and executes it as each line ofcode is run. The conversion process isperformed each time the program needs to be run.

Front 40

Debugger

Back 40

Aprogram which helps locate, identify and rectify errors in a program

Front 41

Translators

Back 41

A program which converts high-level or assembly-level code into executable machine code by compiling or interpreting.

Front 42

Loader

Back 42

Aprogram which loads previously compiled code into memory

Front 43

Linker

Back 43

A program which allows previously compiled code, from software libraries, to be linked together

Front 44

Trace

Back 44

Afacility which displays the order in which the lines of a program are executed,and possibly the values of variables as the program is being run

Front 45

Breakpoint

Back 45

Afacility which interrupts a programon a specific line of code, allowing the programmer to compare the values ofvariables against expected values. Theprogram code can then usually be executed one line at a time. This is called single-stepping

Front 46

Variable watch

Back 46

Afacility which displays the current value of any variable. The value can be 'watched' as the programcode is single-stepped to see the effects of the code on the variable.