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Computer Science AQA A level


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Will Parker


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[Front]


What type of system software is used by programmers to simplify the process of application development?
[Back]


Libraries

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Computer Science AQA A level - Details

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634 questions
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Define software
Programs of instructions which run on the hardware
How and why are library programs useful for programmers?
It simplifies, and speeds up the process of programming cause they can use already tried and tested code
What does the operating system do
Handles I/O devices Memory management Storage management Processor scheduling Provides an API Interrupt handling
Define application software
Programs written to perform specific user end task
Define system software
The software creates a platform for the other software to run
What controls what: hardware or software?
Software controls the hardware
What is an operating system
Set of programs that lies between the application software and the hardware
Why do we use an operating system?
It allow the end user to control the computer with ease
Put simply what is the role of an operating system?
Hides the complexities of the hardware
What are utility programs?
They're the housekeeping programs
What do library programs contain?
Useful functions that are frequently used by a program
Give some examples of utility program tasks
Encryption Data compression Defragmenting hard drives Data backup
Define hardware
Physical components that make up a device
What are the 4 types of system software
Translator Operating systems (OSs) Utility programs Libraries
What does system software do
Operates, controls and maintains the computer and its components
Whats the differences between an interpreter and a complier?
A comiler produces object code/ excutable file An interpreture does not produce an object code An interpreture analyses a program line by line whereas a compiler does the whole block of code A compiler will not procuce an executable file if an error is found but an interpreture will run the code until the first error is detetced Interpreted code will excute slower than excuting the object code produced by a complier Do not need a compiler to excute a compiled program but when running interpreted code the interpreture always needs to be present Once compiled source code is no longer needed to run the program but an interpreture always needs source code at runtime Compiled code can only excute on a machine with the same processor type whereas interpreted code is more portable
- Give the differences between source code and object code
Source code is written in high-level or assembly language whereas object code is written in machine language + all differences between high and low level languages, such as: - Source code is easy to understand - Source code is easy to modify - Source code contains fewer statements than object code
Why does the computer use translators?
In order for a program to be executed by a computer’s processor, it must be in the form of a machine code program
What are the 3 types of translator called?
Interpreter Assembler Compiler
What is source code?
Code written using a human-readable programming language
What is object code?
Code written in machine langauage through translators
What is an intermediate language?
'Half way' standard language which can they be translated into computer specific machine code
What is the benefit of using compilers with intermediate languages?
They allow the program to be run on all platforms
How do compilers with intermediate languages work?
1. Translate the program into the intermediate language 2. Platform specific translator translates this intermediate language code
What is a compliler
A program that translates high level languages into machine code in one go
What is an interpreter
A program that translates high level languages into machine code line by line
What is an assembler
A program that comverts from low level programming code to machine code
Explain how a compiler better protects source code to an interpreture?
A copied file of the code is used to to run the program not the actual source code
Discuss the disadvatages of using a high level language compared to a low level (Assembly language)
Assembly language code may execute more quickly is because translation is not required Assembly language code may use less memory; Assembly language gives direct/better access to computer hardware // enables direct manipulation of memory (contents);
Discuss the advatanges of using a high level language compared to a low level
Program code is easier to understand/maintain/debug; Faster development time // programmers can be more productive // one line of HLL code can do the same job as many lines of assembly language; Programs are (more) portable (to other hardware platforms) Language is problem-oriented; More support/ better refined as more programmers use it; Support for different paradigms; A. Examples eg functional programming Built-in support for data structures; A. Example(s) eg arrays, records Availability of flow control structures; A. Example(s) eg loops, selection Improved features for supporting modularity; A. Ability to use subroutines
What are the two types of low level langauge?
Machine code Assembly language
Describe machine code langauage
Programming with the use of numerical characters
Describe assembly langauage
Programming with the use of mnemonic characters
Explain the term ‘imperative high-level language’
A programming language that requires programming discipline. Programmers must develop a proper order of actions in order to solve the problem. A 'procedural language'
What is a function?
A method that returns a value
What is a procedure?
A method that does not return a value
If you were to want a random number between 0 and 10, how would you go about programming one?
Random random = new Random(); int randomNumber = random.Next(0, 10); Console.WriteLine(randomNumber);
State how to declare a 2D array
Int[,] array = new int[x, y];
How would you acess the eleemts of a text file
String filename = "FILENAME.txt"; StreamReader sr = new StreamReader(filename); while ((line = sr.ReadLine()) != null) { line = each line of text file }
What does the '%' operand do?
Gives the remainder of a number
What does an integer '/' operand do?
Divides two integers and rounds towards zero to give an integer
Math.Round(x,y,z)' What are the variables for x y and z What do they represent in the rounding function
X: Decimal number to be rounded y: Integer, number of decimal places z: Mode, Specification for how to round x if it is midway between two other numbers
What is meant by a subroutine
A named block of code containing a set of instructions desgined to perform a frequenctly use operation
What are two advantages of constants over hard coded values?
Constants can be given names so are easier to for a human to read Constants only need updating at one position in the code
What is meant by concatenation
Joining two or more strings together
Can you say the 4 types of programming paradigm?
Imperative / procedural Functional Declarative Object oriented
What does the ALU do?
Performs arithmetic and logic operations
What are the 3 stages to the fetch section of the Fetch-Execute cycle ?
1. Any data required by the instruction that isn’t present in registers is fetched 2. The instruction is carried out 3. Results of any calculations are stored in general purpose registers or main memory
What is the role of the control unit?
Controls all the differnt parts of the processor
Why are registers really effective for the CPU?
The CPU needs very fast accessible memory and registers are vert fast memory
What are the 5 special purpose registers?
PC (Program counter) CIR (Current instruction register) MAR (Memory address register) MBR (Memory buffer register) SR (Status register)
What does the special register PC do?
Used to hold the memory address of the next or the current instruction to be executed in the fetch-execute cycle Must say both current and next ^
What does the CIR register do?
Holds the instruction that is currently being executed by the processor
What does the memory address register do?
Stores the memory address of a memory location that is to be read from or written to
What does the special MBR register?
Holds the contents of a memory location that has been read from or data that is to be stored.
What does the status register register do?
Contains a number of bits, the values of which can change to indicate the occurrence of an interrupt.
What do the special purpose registers MBR, MAR and CIR stand for?
Memory buffer register Memory address register Current instruction register
What does the system clock do?
Synchronises the components
What is a register?
A memory/storage location inside the processor
Describe what a word is to the processor
The group of bits that is treated as a single unit by the processor
How would you describe what is happening in the AQA assembly language: LDR Rx, <memory reference>
Loading the value stored in the memory location specified by <memory reference> into register x.
What is a core responsible for in a processor?
Completing the Fetch-Execute cycle
What 4 ways can the processor execute data?
Reading operand data in to the accumulator from the RAM Performing arithmetic on operand data Performing logical functions (conditionals / loops) Writing data from the accumulator to the RAM
What is the role of the processor?
To execute program instructions in order to run applications
Name two types of main memory
1. Random access memory (RAM) 2. Read only memory (ROM)
Discuss the advatanges of using a high level language compared to a low level
Program code is easier to understand/maintain/debug; Faster development time // programmers can be more productive // one line of HLL code can do the same job as many lines of assembly language; Programs are (more) portable (to other hardware platforms) Availability of flow control structures; A. Example(s) eg loops, selection Improved features for supporting modularity; A. Ability to use subroutines Built-in support for data structures; A. Example(s) eg arrays, records Language is problem-oriented; Support for different paradigms; A. Examples eg functional programming
Discuss the disadvatages of using a high level language compared to a low level
Assembly language code may execute more quickly; R. If response suggests that faster execution is because translation is not required Assembly language code may use less memory; Assembly language gives direct/better access to computer hardware // enables direct manipulation of memory (contents); NE. “More efficient” for either executes more quickly or uses less memory