Processor Components Flashcards
What is another name for the processor?
CPU (Control Processing Unit)
What does the CPU contain?
Components that allow it to execute instructions
What components does the CPU contain?
Control Bus unit
Buses
Arithmetic Logic Unit
Registers
What is the control Unit responsible for?
For the flow of data between components, it will decode an instruction into several sequential steps, in order to determine how an instruction should be executed.
What is a bus?
A set of parallel lines connecting two or more components in a computer system
What is the processor connected to?
The processor is connected to external components by buses. Buses will connect the CPU to RAM (Main Memory).
When is the address bus used?
The address bus is used when data is to be written or read from a memory location, specifically the address is sent down the address bus.
When is the data bus used?
The data bus is used when the data transmitted to an address has to be performed, meaning it acts as a carry (transport) for information.
When is the control bus used?
When synchronisation and control is provided in the form of signals.
What are data and control buses?
Data and control buses are bidirectional buses meaning they transmit data in both directions between the CPU and a component.
What is the address bus?
It is a single directional bus.
What are the three buses collectively known as?
The system bus
What does it mean for a bus to act as a shared transmission medium?
It means only one bus can be used at any one time
What is the purpose of the CPU?
To provide command, timing and status information
What are the types of status information?
Bus request - Indicates a component is requiring access to the data bus
Bus Grant - The CPU has granted access to the data bus
Memory Read - Data is transferred from a memory location to the data bus
Memory Write - Data is transferred from the data bus to be overwritten to a memory location
Bus Busy - Indicates the data bus is currently busy
Clock - Synchronises operations
Interrupt Request - States that a component is requiring access to the CPU
What is memory divided into?
Memory is divided into units called words.
What is a word?
A word is a fixed sized of digits of bits, this is all treated by the processor as a single unit.
What does each word in memory have?
It has its own location, so the number associated with this word is used as an operand when transmitting data to the processor.
Extra Information*
An operand is part of the binary address of a piece of data or instruction used to give command to what will be done with the opcode. Operand is the first 8 bits of a 10 bit address and the opcode is the piece of data to be worked on, the last two bits in the 10 bit binary address.
How is the address of the word used as an operand?
The instruction which is executed (operand) is stored in that specific location (the location of the word) on the data bus.
What is the ALU?
The arithmetic logic unit, which is used for performing arithmetic operations and logical operations.
What are registers?
Registers act as a fast operating memory location as they are quicker to access than main memory, the registers will temporarily store the results carried out in the ALU.
What will most computers do?
Most computers will make use of a single register called the accumulator.
What is another word for a dedicated register?
Special purpose register.
What is the PC?
Program Counter - used to store the next address of the instruction to be executed, this can be a sequence of instructions, or a branch, where value in the CIR is copied to the Program Counter.
What is the CIR?
The Current Instruction Register. This will hold the current instruction which is executed, the current instruction register will hold or split instruction into its opcode and operand.
What is the MAR?
Memory address Register. The MAR holds the address of the location of which the data is to be written to or retrieved from.
What is the MDR?
The Memory data register, which is used to temporarily store the calculations or output performed in the ALU.
When does the fetch decode and execute cycle repeat?
With each execution of an instruction,
What happens during the fetch phase of the fetch - execute cycle?
The address of the next instruction from the program counter is copied to the MAR.
The value stored at this location is copied to the MDR, which simultaneously increments the value stored in the PC by 1, so it holds the value of the next instruction.
Contents are copied to the CIR.
What happens during the decode phase of the fetch decode execute cycle?
The instruction is split into opcode and operand. Opcode is used to determine the type of instruction or hardware needed to execute it. The operand will include:
- The address of data to be worked on, copied to the MAR.
- The actual data to work with, copied to MDR.
The data to be worked with, transferred to the ALU.
What happens during the execute phase of the fetch - decode - execute cycle?
The appropriate instruction/opcode is performed on the operand.
What is the status register used for?
It is used to hold infromation on the last executed instruction. More specifially they are used for finding errors or exceptions
When does an error occur?
When a further action is required to calculate a certain result
What is an exception?
An event that happens outside of the processor, and it requires the attention of the processor itself.
What happens before the fetch - decode - execute cycle?
The instructions need to be translated to machine code and be present in main memory.
What is the transfer of data given as?
It is given usually as one operation, however it will usually take multiple machine cycles to complete
What does the processor do if it needs to read a memory location?
It will send a read request by the control bus, the address of the location stored on the address bus is returned back to the data bus.
What does the processor do if it needs to write to a memory location?
It sends a read request by the control bus before retrieving data on the data bus.
What is main memory?
This is memory accessed directly by the processor. The main memory will have physical locations so it can be accessed directly with a number.
What is the difference between main memory and secondary storage?
Main memory is accessed directly by the CPU whilst for secondary storage it will not be accessed directly, so an interface is needed called an I/O controller. Another word for main memory is called RAM.
What are external peripheral devices?
Components which distinguish from a computer architecture system such as a printer, they are connected directly to the processor by the I/O controllers
Fact
It is not favourable for the input output controllers to be used to connect external peripherals directly to the processor
What do the I/O controllers consist of?
A series of free locations in memory, where data can be stored from external peripherals to be accessed by the CPU
How are external devices connected?
They are connected by physical ports, the facilitation of data is performed in electronic signal, where the processor when the processor will convert these signals into the correct format.
How to peripheral devices operate?
The external peripheral devices will operate at a lower speed than the processor so the I/O controllers act as an interface that compensates for the time differences
What is the width of a data bus dependent on?
The number of parallel connections. This will determine the number of bits that can be stored on the data bus. This affects processor performance.
How is the width of the address bus determined?
Also by the number of parallel connections, this forms the number of bits that can be used to form an address
Example
So if an address is 2(n) bits, then there are 2^n numbers that will form an address, this will decide the maximum capacity in RAM
State the fetch decode execute cycle of an instruction in full detail. [9]
the fetch part is where the CPU retrieves instruction from memory.The pc holds the address of the next instruction to be executed. then after this the
memory address register stored in the pc is transferred to the Memory Address Register.after the register holds the address of the instruction that needs to be fetched from memory. to fetch the instruction the memory adress is fetched from ram and then it holds the instruction temporarily
In the decode stage, the fetched instruction is interpreted by the CPU to determine what action needs to be performed.
then the ir is fetched from memory and is now stored in the ir where it can be seen.
The Control Unit decodes the opcode.
during the execute stage the alu will see if any operations need to be executed like addition or substraction. data transfer will also happen.
Describe what is meant by RAM [3]
ram is random access memory. it temporarily stores data in your computer.
Explain the purpose of a control bus and where data copied onto data bus from RAM is stored for an integer value used for calculation [1]
control bus contains signals used to synchronize the activities
what is the formula and the maximum number of bits that can be sent on a data bus [2]
2 to the power of n. 2 to the power of 255
