AQA A Level Computer Science Paper 2
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1. Natural Numbers Positive Integers; N = {0, 1, 2, 3, ...}
(N)
2. Integer Numbers Whole numbers; Z = {..., -1, 0, 1, ...}
(Z)
3. Rational Num- Numbers that can be represented as a fraction (all integers are rational)
bers (Q)
4. Irrational Num- Numbers that cannot be represented as a fraction
bers
5. Real Numbers (R) A number that exists (so not a conceptual number like Pi)
6. Ordinal Numbers The positions used in lists (1, 2, 3, ...)
7. Base The number of symbols used to construct values (also referred to as a subscript)
8. Base 2 (Binary) A number system that uses 2 symbols, 0 & 1. Numbers in base 2 are written as
X(v2) such as 11(v2) representing 3.
9. Binary Represen- The Binary system uses 2x to represent numbers, with x increasing by one every
tation of Num- place, starting from the rightmost place. (So 1, 2, 4, 8, 16, 32, 64, 128)
bers
10. Base 10 (Deci- A number system that uses 10 symbols, 0-9. Numbers in base 10 are written as
mal) X(v10) such as 11(v10) representing 11.
11. Decimal Rep- The Decimal system uses 10x to represent numbers, with x increasing by one every
resentation of place, starting from the rightmost place. (So 1, 10, 100)
Numbers
12. Base 16 (Hexa- A number system that uses 16 symbols, 0-9 & A-F. Numbers in base 16 are written
decimal) as X(v16) such as 11(v16) representing 17.
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13. Hexadecimal The Hexadecimal system uses 16x to represent numbers, with x increasing by one
Representation every place, starting from the rightmost place. (So 1, 16, 256)
of Numbers
14. Why use Hex? A hex number is easier to read and remember than binary, and so is quicker to
accurately write or type. It has easy conversion. It is used to define colours, in MAC
addresses and, machine code.
15. Decimal to Bina- From left to right in the place value table, subtract the place value from the decimal
ry Conversion number where possible.
16. Decimal to Hex Divide the decimal number by 16, and add the remainder.
Conversion
17. Significance of 16 16 is 24, meaning that base 16 numbers can be translated from 4 consecutive
bits of a binary value. This makes it simple to translate binary numbers into
hexadecimal values and back again.
18. Bits Each individual digit in a binary digit is referred to as a bit, from the term binary
digit
19. Bytes A collection of 8 bits
20. Kilobyte KB, 10^3 bytes
21. Megabyte MB, 10^6 bytes
22. Gigabyte GB, 10^9 bytes
23. Terabyte TB, 10^12 bytes
24. Kibibyte KiB, 2^10 bytes
25. Mebibyte MiB, 2^20 bytes
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26. Gibibyte GiB, 2^30 bytes
27. Tebibytes Tib, 2^40 bytes
28. ASCII Code In 1963, the American Standard Code for Information Interchange, was estab-
lished to encode symbols found in the English alphabet. Important ASCII values:
A = 65, a = 97
29. Unicode The Unicode system was introduced to standardise the encoding of characters
from all languages
30. Transmission er- When data is transmitted, it doesn't always arrive in the same format that it was
rors sent. These errors cause bits to flip from 1s to 0s and vice versa.
31. What causes Electrical interference, power surges, synchronisation issues, broken cables and
Transmission er- connectors
rors?
32. Parity Bits When sending a byte of data, one bit is used as a parity bit. This bit is set to a 1
or 0 to make the total numbers of 1s or 0s in the byte odd or even depending on
the machine. If the wrong number of bits are 'on', an error has occurred.
33. Majority Voting Each bit of a message is sent three times- if a bit value is flipped erroneously, the
recipient computer uses the majority rule and assumes that two bits that have not
changed were therefore correct.
34. Check Digits A check digit is an additional digit at the end of a string of other numbers designed
to check for mistakes in input or transmission. The first 12 digits are the unique
number, and the 13 is a check digit calculated by an algorithm based on the other
12 digits
35. Modulus 10 Add all the numbers, find the remainder when divided by 10, subtract remainder
from 10. Used in check digits
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36. Check Sums A total sum of all bytes is calculated with an algorithm and sent with the data. The
receiving computer recalculates the checksum based on the data it received and
compares it with the checksum received. If it does not match, that data may have
been corrupted, and data is resent.
37. Binary Addition: 0
0+0=
38. Binary Addition: 1
0+1=
39. Binary Addition: 10
1+1=
40. Binary Addition: 11
1+1+1=
41. Overflow Error When the result of an operation is too large for the number of bits the computer
works with
42. Underflow Error When the result of an operation is too small for the number of bits the computer
works with
43. Binary Multiplica- 0
tion: 0 * 0 =
44. Binary Multiplica- 0
tion: 0 * 1 =
45. Binary Multiplica- 1
tion: 1 * 1 =
46. Two's Comple- A way of showing negatives in binary. The MSB is always 1 when a binary number
ment is negative (a sign bit). After writing the positive version, the complement can be
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1. Natural Numbers Positive Integers; N = {0, 1, 2, 3, ...}
(N)
2. Integer Numbers Whole numbers; Z = {..., -1, 0, 1, ...}
(Z)
3. Rational Num- Numbers that can be represented as a fraction (all integers are rational)
bers (Q)
4. Irrational Num- Numbers that cannot be represented as a fraction
bers
5. Real Numbers (R) A number that exists (so not a conceptual number like Pi)
6. Ordinal Numbers The positions used in lists (1, 2, 3, ...)
7. Base The number of symbols used to construct values (also referred to as a subscript)
8. Base 2 (Binary) A number system that uses 2 symbols, 0 & 1. Numbers in base 2 are written as
X(v2) such as 11(v2) representing 3.
9. Binary Represen- The Binary system uses 2x to represent numbers, with x increasing by one every
tation of Num- place, starting from the rightmost place. (So 1, 2, 4, 8, 16, 32, 64, 128)
bers
10. Base 10 (Deci- A number system that uses 10 symbols, 0-9. Numbers in base 10 are written as
mal) X(v10) such as 11(v10) representing 11.
11. Decimal Rep- The Decimal system uses 10x to represent numbers, with x increasing by one every
resentation of place, starting from the rightmost place. (So 1, 10, 100)
Numbers
12. Base 16 (Hexa- A number system that uses 16 symbols, 0-9 & A-F. Numbers in base 16 are written
decimal) as X(v16) such as 11(v16) representing 17.
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13. Hexadecimal The Hexadecimal system uses 16x to represent numbers, with x increasing by one
Representation every place, starting from the rightmost place. (So 1, 16, 256)
of Numbers
14. Why use Hex? A hex number is easier to read and remember than binary, and so is quicker to
accurately write or type. It has easy conversion. It is used to define colours, in MAC
addresses and, machine code.
15. Decimal to Bina- From left to right in the place value table, subtract the place value from the decimal
ry Conversion number where possible.
16. Decimal to Hex Divide the decimal number by 16, and add the remainder.
Conversion
17. Significance of 16 16 is 24, meaning that base 16 numbers can be translated from 4 consecutive
bits of a binary value. This makes it simple to translate binary numbers into
hexadecimal values and back again.
18. Bits Each individual digit in a binary digit is referred to as a bit, from the term binary
digit
19. Bytes A collection of 8 bits
20. Kilobyte KB, 10^3 bytes
21. Megabyte MB, 10^6 bytes
22. Gigabyte GB, 10^9 bytes
23. Terabyte TB, 10^12 bytes
24. Kibibyte KiB, 2^10 bytes
25. Mebibyte MiB, 2^20 bytes
, AQA A Level Computer Science Paper 2
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26. Gibibyte GiB, 2^30 bytes
27. Tebibytes Tib, 2^40 bytes
28. ASCII Code In 1963, the American Standard Code for Information Interchange, was estab-
lished to encode symbols found in the English alphabet. Important ASCII values:
A = 65, a = 97
29. Unicode The Unicode system was introduced to standardise the encoding of characters
from all languages
30. Transmission er- When data is transmitted, it doesn't always arrive in the same format that it was
rors sent. These errors cause bits to flip from 1s to 0s and vice versa.
31. What causes Electrical interference, power surges, synchronisation issues, broken cables and
Transmission er- connectors
rors?
32. Parity Bits When sending a byte of data, one bit is used as a parity bit. This bit is set to a 1
or 0 to make the total numbers of 1s or 0s in the byte odd or even depending on
the machine. If the wrong number of bits are 'on', an error has occurred.
33. Majority Voting Each bit of a message is sent three times- if a bit value is flipped erroneously, the
recipient computer uses the majority rule and assumes that two bits that have not
changed were therefore correct.
34. Check Digits A check digit is an additional digit at the end of a string of other numbers designed
to check for mistakes in input or transmission. The first 12 digits are the unique
number, and the 13 is a check digit calculated by an algorithm based on the other
12 digits
35. Modulus 10 Add all the numbers, find the remainder when divided by 10, subtract remainder
from 10. Used in check digits
, AQA A Level Computer Science Paper 2
Study online at https://quizlet.com/_f1t7uu
36. Check Sums A total sum of all bytes is calculated with an algorithm and sent with the data. The
receiving computer recalculates the checksum based on the data it received and
compares it with the checksum received. If it does not match, that data may have
been corrupted, and data is resent.
37. Binary Addition: 0
0+0=
38. Binary Addition: 1
0+1=
39. Binary Addition: 10
1+1=
40. Binary Addition: 11
1+1+1=
41. Overflow Error When the result of an operation is too large for the number of bits the computer
works with
42. Underflow Error When the result of an operation is too small for the number of bits the computer
works with
43. Binary Multiplica- 0
tion: 0 * 0 =
44. Binary Multiplica- 0
tion: 0 * 1 =
45. Binary Multiplica- 1
tion: 1 * 1 =
46. Two's Comple- A way of showing negatives in binary. The MSB is always 1 when a binary number
ment is negative (a sign bit). After writing the positive version, the complement can be
