Processor Components Flashcards
What does CPU stand for?
Central Processing Unit
What are some of there components that enable the CPU to carry out its task of executing instructions?
Control unit, buses, ALU, dedicated registers
What does ALU stand for?
Arithmetic/Logic Unit
What does the control unit do?
Controls and coordinates the actives of the CPU, directing the flow of data between the CPU and other devices
What does the control unit do to the next instruction?
It accepts the next instruction, decodes it into several sequential steps, manages its execution and stores the resulting data back in memory or registers
What is a bus?
A set of parallel wires connecting two or more components of a computer
What is the three separate buses that connect the processor to main memory?
Address Bus, Data Bus, Control Bus
When does the CPU use the address bus?
When the CPU wishes to access a particular main memory location, it send this address to memory on an address bus
When does the CPU use the data bus?
The data that is sent to get on the address bus is then return to the CPU on the data bus
When does the CPU use the control bus?
Control signals are sent along the control bus
What are the three buses collectively known as?
System Bus
Why can they only transmit along a bus at any one time?
Each bus is a shared transmission medium
What is the only signal that travels one way along?
Address signals
What direction bus is the control bus?
The control bus is a bi-directional bus (signals can be carried in both directions)
Why must control lines be provided?
To ensure that access to the use of data and address buses by different components does not lead to conflict
What is the purpose of the control bus?
To transmit command, timing and septic status information between system components
In the control bus what does the Bus Request do?
Indicates that a device is request the user of the data bus
In the control bus what does the Bus Grant do?
Indicates that the CPU has granted access to the data bus
In the control bus what does the Memory Write do?
Causes data on the data bus to be written into the addressed location
In the control bus what does the Memory Read do?
Causes data from the addressed location to be placed on the data bus
In the control bus what does the Interrupt Request do?
Indicates that a device is requesting access to the CPU
In the control bus what does the Clock do?
Used to synchronise operations
what are the main control lines in the control bus?
Bus Request, Bus Grant, Memory Write, Memory Read, Interrupt Request and Clock
What are the units memory is divided into called?
Words
What is a word?
A fixed size group of digits, typically 16,32 or 64 bits, which is handled as a unit by the processor
What does each word has it own independent of?
Specific address
Why does the address bus transmit the memory addresses of words that are used as operands in program instructions?
So the data can be retrieved and sent back to the processor
What Instructions can the ALU do?
ADD, SUBTRACT, MULTIPLY, DIVIDE on fixed or floating point numbers
What operations can the ALU do within a register?
Shifting bits to the left or the right
What Boolean logic operations can the ALU perform?
Comparing two values and using operator such as AND, OR, NOT, XOR
What is a register?
Registers are special memory cells that operate at very high speeds, with all arithmetic, logical or shift operation temporally being stored here
What is a accumulator?
a type of register for short-term, intermediate storage of arithmetic and logic data in a computer’s central processing unit (CPU)
What is other special-purpose registers?
Program Counter (PC), Current Instruction Register (CIR), Memory Address Register (MAR), Memory Data Register (MDR)
What does the PC do?
Holds the address of the next instruction to be executed
What does the CIR do?
Holds the current instruction being executed, divided into operand and opcode
What does the MAR do?
Holds the address of the memory location from which data is to be fetched or which data is written to
What does the MDR do?
Used to temporarily store the data read from or written to?
What is MDR also known as?
Memory buffer register
What does FDE stand for?
Fetch-Decode-Execute cycle
When does the FDE cycle repeat?
The cycle is repeated over and over as each instruction of the program is executed
How many phases are part of the Fetch Phase of the FDE?
3
How many phases are part of the Decode Phase of the FDE?
1
How many phases are part of the Execute Phase of the FDE?
1
How may phases of the FDE is there?
5
What is the first step of the FDE?
The address of the next instruction is copied from the PC to the MAR
What is the second step of the FDE?
The instructions held at the MAR address is copied to MDR, simultaneously the content of the PC is incremented, normally by 1, so it holds the address of the next instruction
What is the third step of the FDE?
The contents of the MDR are copied into the CIR
What is the fourth step of the FDE (the Decode phase)?
The instructions held in the CIR is decoded and split into opcode and operand
What does spitting the instruction into opcode do?
Opcode is used to determine the type of instruction and what hardware to use to execute it
In the fourth step of FDE what does the operand hold?
The address of the data to be used with the operation, which then copied to the MAR or the actual data to be operated on, which be copied to the MDR, the data t be operated on may be passed to the ALU/accumulator
What is the fifth step of the FDE (the execute phase)?
The appropriate instructions/opcode is carried out on the operand
