Revision Session

Lesson – revision topics

Areas you need to revise from Quizizz/Forms work

Topic 1: Variables & Constants (1)

All programs will usually have constants and/or variables declared within them

 Constant – value set by the developer when they are coding, cannot be

changed

 Variable – like a “box” which can hold data within a program. These can be

changed when the program is running.

Data types represent the data which can be stored within a constant or
variable. You need to know the following five data types for the exam:

 Character: single letters, numbers or symbols e.g. “1”, “d”, “!”

 Single byte (8 bits) in size

 String: a series of characters e.g. “Dave1!”

 Size varies, but 8 bits (1 byte) per character

 Integer: a whole number e.g. 22, 66, 12

 Usually 2 or 4 bytes per number

 Real: Number with decimal point, e.g. 3.14, 2.456

 Implemented in VB as “single” (4 byte) or “double” (8 byte)

Topic 1: Variables & Constants (2)

Variable Scope can be Global (visible everywhere) or Local (visible only in the procedure they are declared in):

Topic 1: Variables & Constants (3)

As well as “simple” data types, there are more complex
data structures developers can use. Two of these are
Records and Arrays

 Records are “rows” in a database

 they store data in tables and fields. They can be accessed

(read from or written to) in program code

 Arrays can hold many values (normal variables only hold

one).

 They can have one or more “dimensions”, a one-

dimensional array is like a list (a String is an array of
characters), a two-dimensional one is like a table.

 Array elements are accessed by their index

 in a 1 dimensional array MyArray, MyArray(0) is the first

value

 In a 2 dimensional array MyArray(0,1) is the value in the first

row, second column

1-dimensional array. Declare like this:
MyArray = array[9] of Character

2-dimensional array. Declare like this:
MyArray = Array[3, 3] of Integer

Multiple Choice

What is the most appropriate variable to store a person's age?

• String

• Character

• Integer

• Real

Dropdown

I can be amended and can be accessed from anywhere in the module. What am I? ​

Select answer

Dropdown

I cannot be amended and can only be accessed from within a single procedure​. What am I?

Select answer

​

Topic 2: CPU / Computer Architecture (1)

Parts of a CPU (Central Processing Unit) you need to know:

Control unit –sends
commands (via the control
bus to other devices

ALU – carries out arithmetical
and logical operations

Registers are temporary
memory on the CPU used to
store and retrieve values

Topic 2: CPU / Computer Architecture (2)

Buses look like this

and not like this

(on a computer anyway). There are three you need to know about:

Carries information about where data will be
stored in memory

Carries data from memory/input and output
devices in bulk

Carries commands to co-ordinate the
computer’s components

Topic 2: CPU / Computer Architecture (3)

Clock Speed, bus width and cores

 Clock speed is the speed at which the PC operates. It is measured in GHz

 For example a 3.4GHz PC can execute 3,400,000,000 cycles per second

 Faster processor = more heat and more energy used

 Bus width represents the number of instructions which can be processed

simultaneously.

 For example a 64-bit computer can process twice as much information as a 32-bit computer

 Number of cores is the number of processors on a CPU chip.

In general the higher these values are, the faster the PC will be

Match

Match the following buses to their functions

• Control Bus

• Address bus

• Data bus

Carries commands which co-ordinate components

Carries information about where data is stored in memory

Carries data in bulk from memory and I/O

• Carries commands which co-ordinate components

• Carries information about where data is stored in memory

• Carries data in bulk from memory and I/O

Match

Match the following CPU architecture terms to their definitions

• Cores

• Bus width

• Cache

• Clock speed

The number of processors on a chip (typically 4)

The number of bits which can be processed in one cycle (measured in "bits", e.g. "32-bit")

Temporary memory stored in the CPU (measured in kilobytes or megabytes)

Number of cycles per second (measured in GHz)

• The number of processors on a chip (typically 4)

• The number of bits which can be processed in one cycle (measured in "bits", e.g. "32-bit")

• Temporary memory stored in the CPU (measured in kilobytes or megabytes)

• Number of cycles per second (measured in GHz)

Match

Match the following parts of a processor to their function

• ALU

• Cache

• Control unit

• Registers

• Heat sink

Performs arithmetic and logical operations

Stores instructions and data for quick access

Manages the operation of the computer

Memory on the chip used to store and retrieve values in calculations

Large surface area designed to cool the CPU

• Performs arithmetic and logical operations

• Stores instructions and data for quick access

• Manages the operation of the computer

• Memory on the chip used to store and retrieve values in calculations

• Large surface area designed to cool the CPU

Dropdown

Which part of the CPU carries out the processing? ​

Select answer

​

Topic 3 – Binary <-> Decimal (1)

We are used to numbers that work like this:

This is how we write 45 (although we usually ignore the leading 0s); (4 x 10) + 5

Binary numbers work like this:

This is 45 in binary

(1x32) + (0x16) + (1x8) + (1x4) + (0x2) + 1 = 45

You might see the leading zeros in binary numbers when they are written

10x10x10 (1000s)

10x10 (100s)

10s

1s

0

0

4

5

2x2x2x2x2x2x2 (128s)

2x2x2x2x2x2 (64s)

2x2x2x2x2 (32s)

2x2x2x2 (16s)

2x2x2 (8s)

2x2 (4s)

2s

1s

0

0

1

0

1

1

0

1

Topic 3 – Binary <-> Decimal (2)

To convert binary to decimal there are two steps:

1. Look at the number and multiply the value by the value of each place (start from the right)

2. Add up the values

Example: 100101

32+4+1 = 37

128

64

32

16

8

4

2

1

0

0

1

0

0

1

0

1

Topic 3 – Binary <-> Decimal (3)

To convert decimal to binary

1.Take the decimal number and put a “1” in the largest box that will “fit”

For example, if the number is 33 then put “1” in the 32 box. If it is 31, put “1” in the 16 box

2.Subtract the number you have put the “1” in then repeat from Step 1 until you reach the 1s box

Example: express 122 in Binary

128 will not “fit into 122. Put “0” in the 128 box and try the next number

64 “fits” into 122. Put “1” in the 64 box and subtract 64 from 122, leaving 58

32 “fits” into 58. Put “1” in the 32 box and subtract 32 from 58, leaving 26

16 “fits” into 26. Put “1” in the 16 box and subtract 16 from 28, leaving 10



8 “fits” into 10. Put “1” in the 8 box and subtract 8 from 10, leaving 2

4 will not “fit” into 2. Put “0” in the 4 box and try the next number

2 “fits” into 2. Put “1” in the 2 box and subtract 2 from 2, leaving 0

Since there is nothing left, put “0” in the 1 box

128

64

32

16

8

4

2

1

0

1

1

1

1

0

1

0

Multiple Choice

Convert the following binary number to decimal (base 10): 1011 1101

• 72

• 43

• 189

• 255

Multiple Choice

Convert the following binary number to decimal (base 10): 0000 1111

• 255

• 1111

• 9

• 15

Multiple Choice

Convert 255 to binary

• 1111 1111

• 0000 0000

• 1010 1010

• 0101 0101

Multiple Choice

Convert 77 to binary

• 1011 1110

• 0100 0000

• 0100 1101

• 1111 1111