Consider the following processor design characteristics. I. Register-to-register arithmetic operations only II. Fixed-length instruction format III. Hardwired control unit Which of the characteristics above are used in the design of a RISC processor?

Key characteristics of a Reduced Instruction Set Computer (RISC) architecture include:

1. Load/Store architecture: Arithmetic and logical operations are performed only on data stored in registers (register-to-register operations). Only specific load and store instructions access memory (Characteristic I).

2. Fixed-length instructions: Instructions typically have a standard fixed size (e.g., 32 bits), which simplifies instruction decoding and pipelining (Characteristic II).

3. Hardwired control unit: RISC uses simple instructions executed in a single cycle, which are most efficiently implemented using a fast hardwired control unit rather than microprogrammed control (Characteristic III).

Since all three characteristics (I, II, and III) are core design principles of RISC processors, D is the correct option.