1.1.1 - CPU, ALU, Registers, Buses, FDE Cycle Flashcards
(25 cards)
CPU - What is it?
The Central Processing Unit is a processor that has a number of components which enable it to execute instructions.
CPU - What are it’s components?
- Control Unit
- Buses
- ALU (Arithmetic Logic Unit)
- Registers
Control Unit - What is it and What does it do?
A component on the CPU that controls and coordinates activity of the CPU. Directs the flow of data between the CPU and other devices.
Control Unit - Process
- Accepts next instructions
- Decodes it into separate steps
- Manages it’s execution
- Stores the result in memory or registers
Buses - What are they?
A set of parallel wires connecting two or more components of a computer. They are essentially paths that allow data to flow across.
Buses - Process
The processor is connected to the main memory by three separate buses. When the CPU wants to access a main memory location it sends the address to the address bus. The data in that location is returned to the CPU on the data bus. Control signals are sent along the control bus.
Buses - Control Bus | What is it used for?
Used to transmit a command, timing and status info between components. Data can flow along the control bus both ways. Control lines are provided to stop conflict.
Buses - Data Bus | What is it used for?
Used for moving data and instructions between components. Data can flow both ways along the data bus.
Buses - Address Bus | What is it used for?
Used to store memory addresses from which data will be fetched or sent and stored
Buses - Address Bus | What are words and what do they do?
Memory is divided into units called words. A word is a fixed size group of digits. Each word in memory has it’s own address and the address bus transmits the memory addresses of words that are used as operands in program instructions.
ALU - What does it do?
The arithmetic logic unit performs logical operations on the data such as ADD, SUBTRACT, MULTIPLE or DIVIDE. It can also perform shift operations which is shifting bits to the left or right within a register and can carry out Boolean logic operations comparing two vales using operations such as AND, OR, NOT
Registers - What are they?
Special memory cells that operate at high speed
Registers - What are stored in them?
Results of all arithmetic, logical or shift operations are temporarily stored in registers
Registers - Accumulator | What is it and what does it store?
A simple register that stores all the results from operations.
Registers - What are some examples of special purpose registers?
- Program Counter (PC)
- Current Instruction Register (CIR)
- Memory Address Register (MAR)
- Memory Data Register (MDR)
Registers - Program Counter | What does it do?
Holds the address of the next instruction to be executed
Registers - CIR | What does it do?
Holds the current instruction being executed in the format of operand and opcode
Registers - MAR | What does it do?
Holds the address of the memory location from which data is to be fetched or written
Registers - MDR | What does it do?
Temporarily holds the data read from or written to memory. AKA Memory Buffer Register
Fetch Decode Execute Cycle - What is it?
A sequence of operations involved in executing an instruction
FDE Cycle - What are the steps of the fetch phase?
- The address of the next instruction is copied from the PC to the MAR
- The instructions held at that address is copied to the MDR and the PC is incremented by 1 and gets a new address
- The contents of the MDR are copied to the CIR
FDE Cycle - What are the steps of the decode phase?
- The instruction held in the CIR is decoded then the instruction is split into opcode and operand and the opcode is used to determine the type of instruction and what hardware is used to execute it.
FDE Cycle - What are the steps of the execute phase?
- The appropriate instruction/opcode is carried out on the operand
Opcode - What is it?
Operation code is an instruction that can be executed by the CPU
