What is the classical difference between MMID (multiple instructions, multiple data) and SIMD (single instruction, multiple data)?

Discuss the following questions:

What is the classical difference between MMID (multiple instructions, multiple data) and SIMD (single instruction, multiple data)?
What is the difference between the concept of control points and the generation of control signals using hardwired or microprogrammed implementations?
What are the physical limitations of electronic circuits?
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