1 Exampromax - Stuvia US
GCSE Edexcel Computer Science Questions
and Answers 100% Correct Answers Already
Graded A+
Q: Explain how binary is used to represent data (numbers, text, sound,
graphics) and program instructions
Ans: binary is used to represent all elements in a computer
It is stored as a series of 0s and 1s
These relate to the position of transistors (on or off)
All analogue data stored is converted into digital (binary)
Exampromax - Stuvia US
Q: Explain the difference between unsigned and signed integers
Ans: An unsigned integer can only represent positive values
A signed integer can represent positive and negative values
Both unsigned and signed integers are as accurate
Both unsigned and signed integers can have overflow errors
Unsigned integers store more positive values (unsigned is 0 to 255, signed is -127
to 127)
Both unsigned and signed integers use a parity bit
Parity bits are used to check the binary value transmitted is correct
Q: Explain how sign and magnitude is used to represent positive and
negative values 0
Ans: Explain how sign and magnitude is used to represent positive and negative
values
Q: Explain how 2's complement is used to represent negative values
Ans: To convert a binary value into two's complement
...flip the value of each bit (0 becomes 1, 1 becomes 0)
Add 1 to the flipped value
Q: Explain how to convert from binary to denary (decimal)
, 2 Exampromax - Stuvia US
Ans: Write out the headings for the binary value, starting with 1 on the right-
hand side
...usually finishing at 128
...add up the headings with 1 values beneath them
Q: Explain how to convert from denary (decimal) to binary
Ans: Write out the headings from 1 to 128, starting on the right-hand side
...assume the denary value you are converting is an amount of money
...You want to purchase the most expensive headings you can
...remember to calculate the remainder (subtraction)
...if you can purchase a heading it gets a 1 below it
...if you cannot purchase a heading it get a 0 below it
...when you finish you should have no money left
Q: Explain how to add two binary values together
Ans: Four rules that need to be followed to add binary values
Exampromax - Stuvia US
...0 + 0 = 0
...1 + 0 = 1
...1 + 1 = 10 (0, carry 1)
...1 + 1 + 1 = 11 (1, carry 1)
Q: Explain the concept of overflow
Ans: Overflow error occurs when the result cannot fit into the size of the
location assigned to hold it
The computer will ignore the overflow digit
If an overflow error is ignored this compounds errors in subsequent calculations,
which can snowball
Q: Explain what affect left and right shifts have on binary values
Ans: Logical shift left multiplies the number by 2 for each shift
Logical shift right divides the number by 2 for each shift
Q: Explain how to convert between hexadecimal and binary values
Ans: Each 4 bits of binary represents 1 bit of hexadecimal
If the converted binary value is between 0 and 9, it stays the same (0100 = 4 = 4)
If the converted binary value is between 10 and 15, it changes to a letter (1010 =
10 = A, 1111 = 15 = F)
Q: Explain why hexadecimal notation is used
, 3 Exampromax - Stuvia US
Ans: Hexadecimal is used as a short-hand for binary
Hexadecimal is used so humans find it easier to read
Hexadecimal is usually used by computers to display error code numbers
Hexadecimal is used to represent numerical values in assembly languages and
24bit colour codes
Hexadecimal is only used by humans as computers only ever use binary
Q: Explain how computers encode characters using ASCII
Ans: Each character has a unique binary code
This unique code is sent by the keyboard to the computer
The ASCII code for A is 65 (in binary 0100 0001)
Codes for other binary numbers can be found from A (B is 66, C is 67, D is 68,
etc)
ASCII codes for letters are always represented as 8 bit binary values (e.g. 0100
0001)
Exampromax - Stuvia US
Q: Explain the difference between ASCII and UNICODE
Ans: ASCII can represent 127 different characters
...the 8th bit it used as a checksum
UNICODE uses 16 bit instead of 8 bit
...this means it can represent 65,536 different characters
...this can include elements from other languages, symbols, and maths characters
Q: Explain what pixels are (in relation to bitmap images)
Ans: Pixels are the smallest elements of a bitmap image and the smallest parts
that can be displayed on a screen
Q: Explain what resolution is (in relation to bitmap images)
Ans: The resolution of an image is based on the number of elements used to
represent the full image
...the higher the number of elements for a given size, the better the quality of the
image
Resolution is the number of pixels per inch when the image is displayed (on a
monitor, or on paper)
Q: Explain what colour depth is (in relation to bitmap images)
Ans: Colour depth indicates the number of bits used to represent the colour of a
picture element
...the higher the number of bits used, the greater the range of colours
GCSE Edexcel Computer Science Questions
and Answers 100% Correct Answers Already
Graded A+
Q: Explain how binary is used to represent data (numbers, text, sound,
graphics) and program instructions
Ans: binary is used to represent all elements in a computer
It is stored as a series of 0s and 1s
These relate to the position of transistors (on or off)
All analogue data stored is converted into digital (binary)
Exampromax - Stuvia US
Q: Explain the difference between unsigned and signed integers
Ans: An unsigned integer can only represent positive values
A signed integer can represent positive and negative values
Both unsigned and signed integers are as accurate
Both unsigned and signed integers can have overflow errors
Unsigned integers store more positive values (unsigned is 0 to 255, signed is -127
to 127)
Both unsigned and signed integers use a parity bit
Parity bits are used to check the binary value transmitted is correct
Q: Explain how sign and magnitude is used to represent positive and
negative values 0
Ans: Explain how sign and magnitude is used to represent positive and negative
values
Q: Explain how 2's complement is used to represent negative values
Ans: To convert a binary value into two's complement
...flip the value of each bit (0 becomes 1, 1 becomes 0)
Add 1 to the flipped value
Q: Explain how to convert from binary to denary (decimal)
, 2 Exampromax - Stuvia US
Ans: Write out the headings for the binary value, starting with 1 on the right-
hand side
...usually finishing at 128
...add up the headings with 1 values beneath them
Q: Explain how to convert from denary (decimal) to binary
Ans: Write out the headings from 1 to 128, starting on the right-hand side
...assume the denary value you are converting is an amount of money
...You want to purchase the most expensive headings you can
...remember to calculate the remainder (subtraction)
...if you can purchase a heading it gets a 1 below it
...if you cannot purchase a heading it get a 0 below it
...when you finish you should have no money left
Q: Explain how to add two binary values together
Ans: Four rules that need to be followed to add binary values
Exampromax - Stuvia US
...0 + 0 = 0
...1 + 0 = 1
...1 + 1 = 10 (0, carry 1)
...1 + 1 + 1 = 11 (1, carry 1)
Q: Explain the concept of overflow
Ans: Overflow error occurs when the result cannot fit into the size of the
location assigned to hold it
The computer will ignore the overflow digit
If an overflow error is ignored this compounds errors in subsequent calculations,
which can snowball
Q: Explain what affect left and right shifts have on binary values
Ans: Logical shift left multiplies the number by 2 for each shift
Logical shift right divides the number by 2 for each shift
Q: Explain how to convert between hexadecimal and binary values
Ans: Each 4 bits of binary represents 1 bit of hexadecimal
If the converted binary value is between 0 and 9, it stays the same (0100 = 4 = 4)
If the converted binary value is between 10 and 15, it changes to a letter (1010 =
10 = A, 1111 = 15 = F)
Q: Explain why hexadecimal notation is used
, 3 Exampromax - Stuvia US
Ans: Hexadecimal is used as a short-hand for binary
Hexadecimal is used so humans find it easier to read
Hexadecimal is usually used by computers to display error code numbers
Hexadecimal is used to represent numerical values in assembly languages and
24bit colour codes
Hexadecimal is only used by humans as computers only ever use binary
Q: Explain how computers encode characters using ASCII
Ans: Each character has a unique binary code
This unique code is sent by the keyboard to the computer
The ASCII code for A is 65 (in binary 0100 0001)
Codes for other binary numbers can be found from A (B is 66, C is 67, D is 68,
etc)
ASCII codes for letters are always represented as 8 bit binary values (e.g. 0100
0001)
Exampromax - Stuvia US
Q: Explain the difference between ASCII and UNICODE
Ans: ASCII can represent 127 different characters
...the 8th bit it used as a checksum
UNICODE uses 16 bit instead of 8 bit
...this means it can represent 65,536 different characters
...this can include elements from other languages, symbols, and maths characters
Q: Explain what pixels are (in relation to bitmap images)
Ans: Pixels are the smallest elements of a bitmap image and the smallest parts
that can be displayed on a screen
Q: Explain what resolution is (in relation to bitmap images)
Ans: The resolution of an image is based on the number of elements used to
represent the full image
...the higher the number of elements for a given size, the better the quality of the
image
Resolution is the number of pixels per inch when the image is displayed (on a
monitor, or on paper)
Q: Explain what colour depth is (in relation to bitmap images)
Ans: Colour depth indicates the number of bits used to represent the colour of a
picture element
...the higher the number of bits used, the greater the range of colours
