Section 1 - Chapter 1: Processor Components Flashcards
What is a CPU and what does it compose of?
The CPU, also known simply as the processor, has a number of different components which enable it to carry out its task of executing instruction. These components include:
- control unit
- buses
- arithmetic logic unit (ALU)
- dedicated registers
What is the role of the control unit?
The control unit coordinates and controls the activities of the CPU, by directing the flow of data between the CPU and other devices. It accepts the next instruction, decodes it and manages its execution, storing the resulting data back in memory or registers.
What is a bus?
A bus is a set of parallel wires connecting two or more components of a computer. It typically consists of 8,16,32 or 64 lines.
How do buses work?
When the CPU wishes to access a particular main memory location, it sends this address to memory on the address bus. The data in that location is then returned to the CPU on the data bus. Control signals are sent along the control bus.
What are the 3 types of buses?
The three types of buses are:
- Control Bus
- Data bus
- Address Bus
These three buses are known collectively as the SYSTEM BUS
Which buses sends/carries signals in both direction?
Control and data bus. The address bus does not.
What is the control bus?
The control bus is a bi-directional bus, meaning that signals can be carried in both directions. The data and address buses are shared by all components of the system.
Why are control lines used?
To ensure access to and use of the data and address buses by the different components of the system does not lead to conflict.
What is the purpose of the control bus?
The purpose of the control bus is to transmit command, timing and specific status information between system compnents.
What do control lines include?
Control lines include:
- 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
- Memory Write: causes data on the data bus to be written into the addressed location
- Memory Read: causes data from the addressed location to be placed on the data bus
- Interrupt Request: indicates that a device is requesting access to the CPU
- Clock: used to synchronize operations
What is the data bus?
The data bus, typically consisting of 8,16,32, 64 separate lines, provides a bi-directional path for moving data and instructions between system components
Address Bus - what is memory divided into?
Memory is divided up internally into units called words
Address Bus - What is a Word?
A word is a fixed size group of digits which is handled as a unit by the processor.
What does the Address Bus do?
The address bus transmits the memory addresses of words that are used as operands in program instructions, so that data can be retrieved and sent back to the processor.
What does the ALU do?
The ALU performs arithmetic and logical operations on the data. It can perform instructions such as:
- ADD, SUBTRACT, MULTIPLY, DIVIDE
- Shift Operations
- And can carry out Boolean logic operations.
What are registers?
Registers are special memory cells that can operate at very high speed.
What are the five types of registers?
- Accumulator
- Program Counter
- Current Instruction Register
- Memory Address Register
- Memory data register
What is an Accumulator?
An Accumulator takes the place of the general-purpose register. It acts as a temporary storage location which holds an intermediate value in mathematical and logical calculations.
What is a Program Counter?
A Program Counter holds the address of the next instruction to be executed.
What is a Current Instruction Register?
It holds the current instruction being executed and divides it into operand and opcode.
What is a Memory Address Register?
It holds the address of the memory location from which data is to be fetched or to which data is to be written
What is a Memory Data Register?
It is used to temporarily store the data read from or written to memory. Also known as a memory buffer register.
What is the Fetch phase?
1) The address of the next instruction is copied from the program counter to the memory address register.
2) The instruction held at that address is copied to the MDR. Simultaneously, the content of the PC is incremented so that it holds the address of the next instruction.
3) The contents of the MDR are copied to the CIR
What is the decode phase?
The instruction held in the CIR is decoded. The instruction is split into opcode and operand and the opcode is used to determine the type of instruction and what hardware to use to execute it. The operand holds either:
- the address of the data to be used with the operation, which is then copied to the MAR, or
- the actual data to be operated on, which will be copied to the MDR
- the data to be operated on may be passed to the ALU/accumulator.
What is the execute phase?
The appropriate instruction/opcode is carried out on the operand.
