The System Unit & Processor Quiz

The System Unit & Processor

• The System Unit houses the main components of a computer system, including the processor, memory, and storage.

The Processor

Control Unit (CU)

• The Control Unit organizes and sequences micro-operations necessary for instruction execution.
• It decodes instructions to determine required actions, such as loading data, performing logic operations, or arithmetic calculations.
• Transmits control signals to and from other components, verifying successful signal delivery and ensuring timely information flow.
• Guarantees that instructions are executed in the correct order.

Arithmetic and Logic Unit (ALU)

• The ALU performs arithmetic and logical operations, including:
  • Addition, subtraction, multiplication, and division.
  • Logical operations: AND, OR, NOT, and XOR.
  • Value comparisons: greater than, less than, equal to.
  • Binary pattern shifts (left and right).

Registers

• Registers are high-speed memory locations within the processor used for temporary data storage.
• General-purpose registers hold intermediate results from computations.
• Special-purpose registers are defined below:
  • Program Counter (PC): Stores the address of the next instruction to be executed.
  • Current Instruction Register (CIR): Holds the currently executing instruction.
  • Memory Address Register (MAR): Contains the address of the memory location to access for load or store operations.
  • Memory Data Register (MDR): Holds data values or instructions being read from or written to memory.
  • Accumulator: Stores results from ALU calculations.
  • Status Register (SR): Contains flags indicating the result state of the last instruction and detects errors or exceptions.

Machine Cycle Steps

Fetch

• Involves several sub-steps:
  • The PC updates to get the address of the next instruction.
  • The CPU sends a memory read request for the address stored in the PC.
  • The fetched instruction is loaded into the Instruction Register (IR).

Decode

• Instruction breakdown to identify the opcode and operands.
• Control signals are generated based on the instruction, directing operations of components like the ALU and registers.

Execute

• The ALU performs the specified operations.
• Data movement occurs between registers and memory as required.
• Input/output operations may take place if specified by the instruction.

Store

• Results from execution are written back to the appropriate register or memory.
• Status flags are updated post-execution to reflect the operation's results.
• Prepares the system for the next machine cycle, beginning again with the fetch step.

Conclusion

• Understanding the processor's structure and how it processes instructions (through the fetch-decode-execute-store cycle) is crucial for grasping basic computer architecture concepts.