1.1.1.1 Components of a Processor

Question 1

What is the Processor?

Answer 1

• The processor is the brain of a computer.
• It executes instructions which allows programs to run.

Question 2

What is the ALU?

Answer 2

• A part of the CPU that performs arithmetic calculations and logical operations on data for the computer programs.

Question 3

What is the purpose of the ALU?

Answer 3

• The ALU completes all of the arithmetical and logical operations.
• Arithmetical operations include all mathematical operations such as addition and subtraction on fixed or floating point numbers.
• Logical operations include boolean
  logic operations such as AND, OR, NOT, and XOR.

Question 4

What is the CU?

Answer 4

• A part of the CPU that controls and manages the execution of instructions.
• It sends control signals to coordinate execution and controls Fetch-Decode-Execute cycles and buses.

Question 5

What is the purpose of the CU?

Answer 5

• The Control Unit is the component of the processor which directs the operations of the CPU.

It has the following jobs:
- Controlling and coordinating the activities of the CPU.
- Managing the flow of data between the CPU and other devices.
- Accepting the next instruction.
- Decoding instructions.
- Storing the resulting data back in memory.

Question 6

What is the purpose of a Register?

Answer 6

• Registers are small memory cells that operate at a very high speed.
• They are used to temporarily store data.
• All arithmetic, logical and shift operations occur in these
  registers.

Question 7

What is the PC?

Answer 7

• A special purpose register that stores the address of the next instruction to be executed.

Question 8

What is the ACC?

Answer 8

• A special register to temporarily store the results of arithmetical and logical operations performed by the ALU.

Question 9

What is the MAR?

Answer 9

• A special register that stores the memory address of a location that is to be read from or written to.

Question 10

What is the MDR?

Answer 10

• A special register that temporarily stores data to be read from or written to the computer’s memory.

Question 11

What is the CIR?

Answer 11

• A special register that stores the current instruction being executed and decoded.
• The instructions are divided into operand and opcode.

Question 12

What are Buses?

Answer 12

• A physical set of parallel wires connecting and carrying groups of bits between several components of a computer.

Question 13

Describe Buses.

Answer 13

• Buses are a set of parallel wires which connect two or more components inside the CPU.
• There are three buses in the CPU: data bus, control bus, and address bus.
• These buses collectively are called the system bus.
• The width of the bus is the number of parallel wires the bus has.
• The width of the bus is directly proportional to the number of bits that can be transferred simultaneously at any
  given time.
• Buses are typically 8, 16, 32 or 64 wires wide.

Question 14

What is the Data Bus?

Answer 14

• A bi-directional bus
• Used for carrying data and instructions between the processor and memory.

Question 15

What is the Address Bus?

Answer 15

• This is the bus used to transmit the memory addresses specifying where data is to be sent to or retrieved from.
• The width of the address bus is proportional to the number of addressable memory locations.

Question 16

What is the Control Bus?

Answer 16

• This is a bi-directional bus used to transmit control signals between internal (CU) and external components to synchronize access and use of data.
• Coordinates the use of the address and data buses and provides status information between system components.

Question 17

What are the Control Signals?

Answer 17

• Bus request:
  Shows that a device is requesting the use of the data bus.
• Bus grant:
  Shows that the CPU has granted access to the data bus.
• Memory write:
  Data is written into the addressed location using this bus.
• Memory read:
  Data is read from a specific location to be placed onto the data bus.
• Interrupt request:
  Shows that a device is requesting access to the CPU.
• Clock:
  Used to synchronize operations.

Question 18

What is Assembly Language?

Answer 18

• Assembly Language is the language used in LMC.
• Assembly code uses mnemonics to represent instructions,
  for example ADD represents addition.
• This is a simplified way of representing machine code.
• The instruction is divided into operand and opcode in the
  Current Instruction Register.
• The operand contains the data or the address of the data upon which the operation is to be performed.
• The opcode (Operation Code) specifies the type of instruction to be executed.