paper 2 - section 7 - data representation

Question 1

what are logic gates?

Answer 1

special circuits built into computer chips. They receive binary data, apply a boolean operation, then output a binary result

Question 2

how many inputs and outputs do NOT gates have?

Answer 2

one of each

Question 3

what do not gates do?

Answer 3

the output is always the opposite value to the input. If 1 is input, it outputs 0. If 0 is input, it outputs 1

Question 4

how many inputs and outputs does an AND gate take?

Answer 4

it takes 2 inputs and gives 1 output

Question 5

what does an AND gate do?

Answer 5

if both inputs are 1, the output is 1, otherwise the output is 0

Question 6

how many inputs and outputs does an OR gate have?

Answer 6

2 inputs and 1 output

Question 7

what does an OR gate do?

Answer 7

if one or more inputs are 1, then the output is 1, otherwise the output is 0

Question 8

what does a NOT gate look like?

Answer 8

a sideways triangle with a small circle at the tip

Question 9

what does the AND gate look like?

Answer 9

the letter D

Question 10

what does an OR gate look like?

Answer 10

an arrowhead

Question 11

what are two-level logic circuits?

Answer 11

logic circuits that require the inputs to pass through a maximum of 2 logic gates to reach the outputs

Question 12

what is the symbol for AND?

Answer 12

/\

Question 13

what is the symbol for OR?

Answer 13

\/

Question 14

what is the symbol for NOT?

Answer 14

¬

Question 15

what is the smallest measure of data?

Answer 15

bits

Question 16

what do computers use to represent the flow of electricity?

Answer 16

binary

Question 17

does a 1 mean electricity is flowing or isn’t flowing?

Answer 17

is flowing

Question 18

does a 0 show that electricity is flowing or that it isn’t flowing?

Answer 18

that it isn’t flowing

Question 19

what is a byte big enough to store?

Answer 19

one character

Question 20

what is the file size of most files (like songs, pictures and documents) measured in?

Answer 20

kB or MB

Question 21

what are high definition videos and complex applications often measured in?

Answer 21

gigabytes

Question 22

what is secondary storage capacity measured in?

Answer 22

gigabytes or terabytes

Question 23

why is each unit 1024 (not 1000) times bigger than the previous unit?

Answer 23

because 1024 is a power of 2 which is helpful when dealing with binary data

Question 24

what is the formula to find out how many different values a data unit can take?

Answer 24

2^n where n is the number of bits

Question 25

what are parity bits used for?

Answer 25

they're used to check for errors

Question 26

what are check digits used for?

Answer 26

check digits are a way of checking that data has been entered and read correctly. They are digits added to the end of numbers (e.g. ISBNs on books) and are calculated using other digits in the number. If the check digit is correct when data is read, then it's likely that the data has been entered/read correctly

Question 27

what is the check digit called for binary data?

Answer 27

a parity bits

Question 28

what is an even parity bit used for?

Answer 28

it is added to make a binary string have an even number of 1s

Question 29

what is an odd parity bit used for?

Answer 29

an odd parity bit is added to make a binary string have an odd number of 1s

Question 30

what would the even parity bit of the 7-bit string 1010010 be?

Answer 30

1010010 has three 1s, so the even parity bit is 1. This is sent as 10100101

Question 31

what would the even parity bit of the 7-bit string 1100101 be?

Answer 31

1100101 has four 1s, so the even parity bit is 0. This is sent as 11001010

Question 32

what would the odd parity bit of the 7-bit string 1010010 be?

Answer 32

it has three 1s, so the odd parity bit is 0. This is send as 10100100.

Question 33

what would the odd parity bit of the 7-bit string 1100101 be?

Answer 33

it has 4 1s, so the even parity bit is 1. This is sent as 11001011.

Question 34

what is the problem with parity bits?

Answer 34

if two bits within the same binary string are read incorrectly then no error will be detected. For example, if an even parity bit is used and the binary string 10100000 is read as 10000100 then no error will be picked up.

Question 35

which denary numbers can 8-bit binary numbers represent?

Answer 35

the denary numbers 0 to 255

Question 36

which denary numbers can 16-bit binary numbers represent?

Answer 36

the numbers 0 to 65,535

Question 37

which denary numbers can 32-bit binary numbers represent?

Answer 37

the numbers 0 to 4,294,967,295

Question 38

when do overflow errors occur?

Answer 38

when a calculation gives a result with more bits than are available to store it. This can be a real problem - programmers must make sure that they can't occur, or that they are dealt with.

Question 39

what is used to show that an overflow error has occured?

Answer 39

overflow flags

Question 40

why are overflow errors a problem?

Answer 40

they can lead to a loss of data and a loss of accuracy in your answer. It could also cause software to crash if it doesn't have a way of dealing with the extra bit.

Question 41

what does a binary shift do?

Answer 41

it moves every bit in a binary number left or right a certain number of places

Question 42

what is another name for a binary shift?

Answer 42

a logical shift

Question 43

what happens to gaps at the beginning or end of the number in a binary shift?

Answer 43

the gaps are filled in with 0s

Question 44

what do left shifts (binary shifts) do?

Answer 44

multiply a binary number. For every place shifted left, the number is doubled.

Question 45

what do right (binary) shifts do?

Answer 45

they divide a binary number. For every place shifted right, the number is halved

Question 46

how many bits is each hex character equal to?

Answer 46

4 bits (a nibble)

Question 47

what are the advantages of using hexadecimal?

Answer 47

- it's simpler to remember large numbers in hex - they're far shorter than binary numbers - due to hex numbers being shorter, there's less chance of input errors - it's easier to convert between binary and hex than binary and denary

Question 48

what do you do if, when you are converting binary to hexadecimal, you can't split the binary number evenly into nibbles?

Answer 48

you add 0s on the front until there is an exact number of nibbles