Answer: (ii) facilitates easy implementation of new instructions

Correct option is (ii).

Explanation:
A microprogrammed control unit generates control signals from microinstructions stored in a Control Memory (control store). Each machine instruction is executed as a sequence of micro-operations defined by firmware.

• Why (ii) is correct: To add a new instruction, only the microprogram in control memory needs to be modified/extended. No hardware rewiring is required, so implementation of new instructions, complex CISC instruction sets, and design changes is flexible and easy. It also simplifies debugging via microcode changes.

• Why other options are wrong:

  • (i) is faster: False. Hardwired CU using combinational logic (gates, encoders) is faster because microprogrammed CU requires fetch of microinstruction from control memory. Microprogrammed is slower.
  • (iii) useful when every small program is to be run: Irrelevant. Control unit type has no relation to running small user programs.
  • (iv) usually refers to CU of microprocessor: False. Both types can be used in microprocessors; this is not a definition.

Hence microprogrammed CU trades speed for flexibility and ease of modification.