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A OCR Computer Science A level > Chapter 1 - Processor components > Flashcards

Chapter 1 - Processor components Flashcards

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1
Q

What is the purpose of the CPU?

1 Mark

A

» Processes instructions using the FDE cycle

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2
Q

What is the purpose of the control unit?

4 Marks

A

» Controls the flow of bits inside the CPU between the registers
» Decodes instructions
» Controls the execution of instructions
» Maintains synchronisaton

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3
Q

What is a bus?

1 Mark

A

» Set of parallel wires/lines connecting 2 or more components of a computer in which data can be sent around the computer

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4
Q

What is an address bus?

1 Mark

A

» A bus used to access a particular main memory location

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5
Q

What is a data bus?

1 Mark

A

» Returns the data of the location to the CPU

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6
Q

What is a control bus?

1 Mark

A

» A bus which carries control signals, and also the clock’s pulses

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7
Q

What is a system bus?

1 Mark

A

» The three buses: control, signal and address

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8
Q

What is a shared transmission medium?

A

» Each bus has one of these, and it means only the device can transmit along a bus at any one time

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9
Q

What is bi-directional ?

1 Mark

A

» Can travel both forwards and backwards

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10
Q

What buses travel in both directions?

2 Mark

A

» Data bus
» Control bus

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11
Q

What is unidirectional?

1 Mark

A

» Data flows in one direction only

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12
Q

Which bus travels in one direction only?

1 Mark

A

» Address bus

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13
Q

Where does the address bus travel to?

A

» To memory or an I/O controller

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14
Q

What is an I/O controller?

1 Mark

A

» A series of micro ships which helps in the communication of data between the CPU and motherboard

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15
Q

What does I/O stand for?

A

» Input and output devices

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16
Q

What is the purposes of control lines in a control bus?

A

» To ensure that access to and use of that data and address buses by the different components of system does not lead to conflict

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17
Q

How can the components of the system buses lead to conflict?

A

» As data and address buses are shared by all components, control lines are needed to regulate the timing signals

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18
Q

What are some examples of control signals?

A

» Bus request
» Bus grant
» Memory Write/Read

19
Q

How many lines usually does a data bus have?

A

» Usually 8,16,32,64 separate lines.

20
Q

What is a word?

1 Mark

A

» Fixed size group of digits that are divided up internally in memory, which has its own specific address

21
Q

What is the purpose of the ALU?

2 Marks

A

» Performs arithmetic and logical operations on the data
» Acts as a gateway to the processor for easy calculations

22
Q

What are registers?

2 Mark

A

» A discrete small piece of memory used for storing data
» Within the processor

23
Q

What is the purpose of the accumulator?

1 Mark

A

» To store the results of the calculations from ALU

24
Q

What is the purpose of program counter?

1 Mark

A

» Stores the address of the next instruction to be processed

25
Q

What is the purpose of the CIR?

1 Mark

A

» Stores the most recently fetched instruction
» Which will be decoded and executed

26
Q

What is the purpose of the MAR?

1 Mark

A

» Contains the address of the data to be accessed from memory

27
Q

What is the purpose of the MDR?

3 Marks

A

» Contains the instruction of the memory location address specified in the MAR
» Acts as a buffer to store instructions and data
» Copies the data into the CIR

28
Q

What is the 1st part of the fetch phase in the FDE cycle?

2 Marks

A

» Address of next instruction is copied from the PC to the MAR
» After being sent to MAR , a read signal is sent across the control bus and the contents of the MAR are sent across the address bus

29
Q

What is the 2nd part of fetch phase in the FDE cycle?

2 Marks

A

» Instruction held at that address is copied to MDR by the data bus and is stored in MDR
» Simulatenously the PC is incremented by 1

30
Q

What is the last phase in the fetch phase of the FDE cycle?

1 Mark

A

» Contents of MDR are copied to CIR

31
Q

What is the 1st phase of the decode phase in the FDE cycle?

1 Mark

A

» Instruction is split into opcode and operand in the CIR

32
Q

What is the operand?

1 Mark

A

» This is the value the instruction uses - it is a value which is manipulated by the CPU

33
Q

What is the Opcode?

1 Mark

A

» Is the part of the instruction that specifies which operation the processor should perform

34
Q

What happens if the Operand is an address?

2 Marks

A

» Passed to MAR, gets to the memory location of the address in RAM
» Reads the value and is sent to the MDR via the data bus, which is copied to the accumulator

35
Q

What is the final phase in the Execute phase in the FDE cycle?

1 Mark

A

» Appropriate instruction/opcode is carried out on the operand

36
Q

What does read command do?

1 Mark

A

» Load data

37
Q

What does write do?

1 Mark

A

» Store data

38
Q

How does the control unit coordinate the activates of the CPU?

2 Marks

A

» Controls the execution of instructions - By sending timing signals
» Send control signals to enable data to be read from and written to main memory

39
Q

Describe what the process of the control bus is

1 Mark

A

» Transmits control signals from the control unit, which contains the timing signals

40
Q

Explain why special registers are needed in addition to primary memory?

2 Marks - To do with cache

A

» Allows fast access to data which is needed frequently
» Faster than acessing RAM

41
Q

Explain 2 reasons why the value held in the register which holds the address of the next instruction be processed may change?

4 Marks

A

» Program counter increments - during FDE cycle
» A jump instruction from the CIR/Operand changes to address given

42
Q

Where does the jump instruction send the address?

3 Marks

A

» Sends to the PC from the CIR
» PC increments by 1
» MDR copies data to CIR

43
Q

Explain the need for the Current Instruction Register (CIR) and describe how the data which it holds is used

A

» Purpose to hold recently fetched instructions ready to be decoded and executed
» Decode phase - CIR splits data into 2 bits
» Opcode and Operand
» Operand is the actual data - the value that will be manipulated by the CPU
» Opcode - It is the instruction which tells the CPU what to do with the instruction
» CIR sends jump instructions also

A OCR Computer Science A level (75 decks)

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