# GCSE Computer Science Paper 1

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• Created by: Lilyk30
• Created on: 14-04-18 10:02
What is an algorithm?
An algorithm is a sequence of steps that can be followed to complete a task
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What is decomposition?
Decomposition means breaking a problem into a number of sub-problems, so that each sub-problem accomplishes an identifiable task, which might itself be further subdivided
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What is abstraction?
Abstraction is the process of removing unnecessary detail from a problem
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What symbol shows the start and the end of a flow diagram?
The oval
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What symbol shows a process in a flow diagram?
The rectangle
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What symbol shows input/ output in a flow diagram?
The parallelogram
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What symbol shows a decision in a flow diagram?
The diamond
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Can more than one algorithm be used to solve the same problem?
Yes
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How would you find out what an algorithm is doing?
Produce a trace table
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How does a linear search work?
Start at the beginning of the array and look at every item until the one you want is found
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How does a binary search work?
Dividing the data list in half and looking at the half that could contain the required data item
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What are the advantages of a linear search?
Easy to understand the concept, memory efficient, resource efficient
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What are the disadvantages of a linear search?
The longer the list, the less efficient it is
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What are the advantages of a binary search?
Much faster, fairly simple, well known
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What are the disadvantages of a binary search?
More complicated than linear, only works on lists that have been sorted into order, won't work on lists where the data is not related
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What is a bubble sort?
Repeatedly going through a list to be sorted, comparing each pair of adjacent elements; if the elements are in the wrong order, they are swapped
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What is a merge sort?
The list is divided in half, forming two sublists, until each sublist only has 1 data piece in it
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What are the advantages of a bubble sort?
Simple to write, easy to understand, only takes a few lines of code
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What are the disadvantages of a bubble sort?
Takes a while to sort; the longer the list, the longer the time taken
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What are the advantages of the merge sort?
Always fast
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What are the disadvantages of the merge sort?
Uses a lot of memory, can slow down when attempting to sort a very large data amount
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What is data type?
Defines the type of data that will be stored at the memory locations
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What is an identifier?
A unique name given to the variable
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What is an integer?
A whole number
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What is a real/float number?
A number with a fractional
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What is a boolean data type?
True/False
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What is a character?
A single character (a,z,r)
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What is a string?
A string of characters
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What is variable declaration?
Declaring a name for a variable is saying what the data type will be and where it will be stored in memory.
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What is constant declaration?
These are sections of program code that define the names that will be used to refer to constants, and what kind of data each of them will hold.
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What is assignment?
Values are assigned t ovariables using an = sign: x = 1
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What is iteration?
When a section of code is repeated a certain number of times or until the condition is true or false
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What is selection?
In a selection structure, a question is asked, and depending on the answer, the program takes one of two courses of action, after which the program moves on to the next event.
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What is a subroutine?
A named, self-contained section of code that performs a specific task
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What is definite iteration?
Operations for a fixed number of repetitions: the for... next loop
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What is indefinite iteration?
Operations continue until the condition is true or false: the while... end while loop
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What is an array?
A list that makes groups of data easy to use
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What are 1- dimensional arrays?
One dimensional array is a list of variables of same type that are accessed by a common name.
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What are 2- dimensional arrays?
A two dimensional array is a group of lists, or arrays that are organized into one data set.
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What are records?
A record is a special type of data structure which, unlike arrays, collects a number of fields of different data types which define a particular structure such as a book, product, person and many others.
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How do you generate a random number?
import random/ print random.randint9(1,100)
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What is the concept of subroutines?
A named block of code that may be executed by simply writing its name in a program statement
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What are the advantages of using subroutines in programs?
Subroutines can be used repeatedly without having to be rewritten each time they are used.
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What are parameters?
A parameter is a special kind of variable, used in a subroutine to refer to one of the pieces of data provided as input to the subroutine.
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What are local variables?
Variables that only exist when the subroutine is executing and are only accessible within the subroutine
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Why is it good to use local variables?
It would be more specific to the subroutine, you would use less memory as it is only stored and created when needed
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What is a range check?
Checks whether a number or date is within a sensible/ allowed range
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What is a type check?
Checks whether data is the right type
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What is a length check?
Checks whether text entered is not too long or too short
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What is a presence check?
Checks that data has been entered
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What is a format check?
Checks the format of the data is appropriate
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What is an authentication routine?
Authentication routines are used to make sure the user logging in to the system is authorised to do so
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What are the main differences between low-level and high-level languages?
High level languages allow much more abstraction than low level languages. This allows algorithms and functions to be written without requiring detailed knowledge of the hardware used in the computing platform.
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What is the difference between machine code and assembly code?
Machine code is the bits and bytes that the processor executes while running its program. Assembly code is a low level symbolic representation of that machine code, making it easier to write.
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What will all code have to be translated into?
Machine code
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What are the advantages of low-level languages?
Writing code in a low-level language allows the programmer to have complete control over the code.
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What are the disadvantages of low-level languages?
Can't be read easily by humans, needs a highly skilled person to use it, takes longer to write
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What are the advantages of high-level languages?
Can be easily writtien and read by humans, less technical skill is required
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What are the disadvantages of high-level languages?
Typically only provide plain text graphics, has to be converted into machine code anyway, takes up more memory
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What does an interpretor do?
Used to translate high-level code into machine code; translates each line of code and then executes it; no object code is produced
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What does a complier do?
Translates high-level code into machine code; can result in lots of different machine codes; the person uying the software cant see the source code
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What does an assembler do?
An assembler converts assembly language into machine code; simple conversion as every assembly language instruction is translated into a single machine code instruction
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What is source code?
The code written by the programmer
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What is object code?
The machine code produced by the complier
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What number base is decimal?
10
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What number base is binary?
2
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What number base is hexadecimal?
16
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Why do computers use binary to represent all data and instructions?
Because the computer is made of switches tha can only be turned on and off so the 0s and 1s represent the states of on and off
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Why is hexadecimal often used in computer science?
Easier for humans to understand
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What is a bit?
The fundemental unit of information; either 1 or 0
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What is a byte?
A group of 8 bits
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Where can binary shifts be used?
Binary shifts can be used to perform simple multiplication /division by powers of 2
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How many characters can the 7-bit ASCII code represent?
128
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How many characters can Unicode represent?
65,536
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Are character codes often grouped and run in sequence when encoding tables?
Yes
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What is the purpose of unicode?
To represent the characters of all languages in the world
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What are the advantages of unicode over 7-bit ASCII?
Unicode can represent more characters
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What is a pixel?
An individual dot that makes up an image
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What is the image resolution?
The width of the image x the height of the image
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What are bitmaps made of?
Pixels
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How can the number of pixels and colour depth affect the size file of a bitmap image?
A higher number of pixels and a hugher colour depth mean a bigger file size
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What is the calculation for bitmap image file size?
width x height x colour depth (/ by 8 if calculating bytes)
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What is sound?
Analogue
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What must sound be converted into to be stored and used in a computer?
Digital
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What happens to soundwaves to create the digital version of sound?
They are sampled
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What is sampling rate?
The number of samples taken in a second, measured in hertz
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What is sample resolution?
The number of bits per sample
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How do you calculate sound file sizes?
File size = sampling rate x sample resolution x number of seconds
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What is data compression?
Making a file smaller by either losing data permenantly or temporarily
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What is the difference between lossy and lossless compression?
Lossy compression is when a file is compressed by removing some of teh detail whereas lossless compression is where files are compressed but no data is lost.
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## Other cards in this set

### Card 2

#### Front

What is decomposition?

#### Back

Decomposition means breaking a problem into a number of sub-problems, so that each sub-problem accomplishes an identifiable task, which might itself be further subdivided

### Card 3

#### Front

What is abstraction?

### Card 4

#### Front

What symbol shows the start and the end of a flow diagram?

### Card 5

#### Front

What symbol shows a process in a flow diagram?

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