Question

In CPU Control design, what is the primary difference between hardwired control and micro programmed control?

• A. Hardwired control uses software programs, while micro programmed control used combinational circuits.
• B. Hardwired control is faster but less flexible, while micro programmed control is slower but easier to modify.
• C. Hardwired control cannot execute arithmetic operations, while micro programmed control can.
• D. Hardwired control uses registers for control signals, while microprogrammed control does not.

Hint:

RISC (Reduced Instruction Set Computer) architectures usually use Hardwired control to maximize speed, whereas CISC (Complex Instruction Set Computer) architectures often use Microprogrammed control to manage complex instruction sets.

Answer 1

The Correct Option is B

Concept: The Control Unit (CU) can be implemented in two major ways to generate the control signals required to execute instructions:
• Hardwired Control: Implemented using physical hardware (logic gates, flip-flops, decoders).
• Microprogrammed Control: Implemented using a "control memory" that stores a sequence of microinstructions.

Step 1: Analyzing Hardwired Control.
Because hardwired control is built directly into the silicon logic, it is extremely fast as signals travel through gates at high speeds. However, because it is physically "wired," changing the instruction set requires a complete redesign of the chip hardware, making it inflexible.

Step 2: Analyzing Microprogrammed Control.
This approach uses a special internal ROM (Control Store). To execute a macroinstruction, the CPU runs a "microprogram." Accessing memory is slower than gate logic, which makes this method slower. However, the instruction set can be changed or updated by simply changing the microprogram in the ROM, which provides high flexibility.

Step 3: Comparing the options.
Option (B) perfectly summarizes the classic trade-off in computer engineering: the choice between the speed of hardware (Hardwired) and the flexibility of software-like control (Microprogrammed).