Accumulator (ACC) - The Result Holder

Accumulator (ACC) - The Result Holder

What It Is:

The Accumulator is a register that stores the results of calculations performed by the ALU. It's a temporary workspace for arithmetic and logic operations.

How It Works:

• Before calculation: ACC may hold one of the operands (e.g., in "ADD 5", ACC holds the current value, 5 is added to it)
• During EXECUTE: The ALU performs the operation
• After calculation: The result is stored in the ACC, overwriting the previous value
• Can be used again: The ACC value can be used in the next operation or stored to memory with a STORE instruction

Key Characteristics:

• Holds data values (not addresses or instructions)
• Updated during the EXECUTE stage of the FDE cycle
• Acts as an implicit operand for many ALU instructions
• Faster than storing results to main memory (RAM)

Real-world analogy: Like a calculator's display screen. When you calculate 5 + 3, the screen shows 8. When you then multiply by 2, the screen updates to 16. The ACC works the same way - showing the current result.