Computer Science Paper 1 questions and
answers
Control Unit - A register in the cpu that controls and coordinates the activities of
the cpu directing the flow of data
Bus - a series of connectors that transfer signals between internal components
Memory Read - causes data from the addressed location in RAM to be placed on
the data bus
Memory Write - Causes data on the data bus to be written into the addressed
location.
Bus Request - Indicates that a device is requesting the use of the data bus
Bus Grant - Indicates that the CPU has granted access to the data bus.
System bus - collective term for address, data and control bus
Data bus - A bi-directional path for moving data and instructions between system
components
,Computer Science Paper 1 questions and
answers
Clock - used to synchronize operations
Control bus - A bi-directional bus to transmit command, timing and specific status
information between system components
Address bus - A one directional bus that transmits memory addresses that are
used as operands in programming instructions, so that data can be retrieved from
main memory
ALU - Arithmetic-Logic unit, preforms logical and arithmetic operations on data
e.g. ADD, SUBTRACT, shift operations or Boolean logic
Registers - High speed memory cells, all arithmetic and logic happens in these,
typically there are 16 general purpose registers in a CPU, they are very fast
Accumulator - A special purpose register which stores the result of calculations
made by the ALU
,Computer Science Paper 1 questions and
answers
Program Counter (PC) - Holds the address of the next instruction to be executed,
this can be the next instruction in a sequence of instructions, or a branch/ jump
Current instruction register (CIR) - stores the actual instruction that is being
decoded
Memory address register (MAR) - stores the address of instructions and data that
need to be fetched from or sent to memory
Memory data register (MDR) - stores the data which is to be sent or fetched from
memory
Interrupt registers - generates and detects interrupts
Fetch Decode Execute register sequence - PC
MAR
Address Bus
Memory
, Computer Science Paper 1 questions and
answers
Data bus
MDR
CIR
Decode Unit
MAR
Address Bus
Main Memory
Fetch phase - - Instructions pulled from memory and stored in main memory.
- Program Counter (a register) stores the address location of the instruction
- Program Counter and instructions are placed in the Instruction Register (IR)
- Program Counter is incremented by 1
Decode phase - 1. Instruction in CIR is decoded
2. Instruction is split into opcode and operand
3. the operand determines the type of instruction
- if its the address of the data used with the operation it is copied into the MAR
- if it the actual data to be operated on it is copied into the MDR
answers
Control Unit - A register in the cpu that controls and coordinates the activities of
the cpu directing the flow of data
Bus - a series of connectors that transfer signals between internal components
Memory Read - causes data from the addressed location in RAM to be placed on
the data bus
Memory Write - Causes data on the data bus to be written into the addressed
location.
Bus Request - Indicates that a device is requesting the use of the data bus
Bus Grant - Indicates that the CPU has granted access to the data bus.
System bus - collective term for address, data and control bus
Data bus - A bi-directional path for moving data and instructions between system
components
,Computer Science Paper 1 questions and
answers
Clock - used to synchronize operations
Control bus - A bi-directional bus to transmit command, timing and specific status
information between system components
Address bus - A one directional bus that transmits memory addresses that are
used as operands in programming instructions, so that data can be retrieved from
main memory
ALU - Arithmetic-Logic unit, preforms logical and arithmetic operations on data
e.g. ADD, SUBTRACT, shift operations or Boolean logic
Registers - High speed memory cells, all arithmetic and logic happens in these,
typically there are 16 general purpose registers in a CPU, they are very fast
Accumulator - A special purpose register which stores the result of calculations
made by the ALU
,Computer Science Paper 1 questions and
answers
Program Counter (PC) - Holds the address of the next instruction to be executed,
this can be the next instruction in a sequence of instructions, or a branch/ jump
Current instruction register (CIR) - stores the actual instruction that is being
decoded
Memory address register (MAR) - stores the address of instructions and data that
need to be fetched from or sent to memory
Memory data register (MDR) - stores the data which is to be sent or fetched from
memory
Interrupt registers - generates and detects interrupts
Fetch Decode Execute register sequence - PC
MAR
Address Bus
Memory
, Computer Science Paper 1 questions and
answers
Data bus
MDR
CIR
Decode Unit
MAR
Address Bus
Main Memory
Fetch phase - - Instructions pulled from memory and stored in main memory.
- Program Counter (a register) stores the address location of the instruction
- Program Counter and instructions are placed in the Instruction Register (IR)
- Program Counter is incremented by 1
Decode phase - 1. Instruction in CIR is decoded
2. Instruction is split into opcode and operand
3. the operand determines the type of instruction
- if its the address of the data used with the operation it is copied into the MAR
- if it the actual data to be operated on it is copied into the MDR
