In computer processors, the data path often consists of the following functional

Question

In computer processors, the data path often consists of the following functional blocks. The instruction register stores the current instruction to be executed. The program counter (PC) stores the address of the next instruction to be fetched. The memory address register (MAR) is a register that either stores the memory address from which data will be fetched to the CPU or the address to which data will be sent and stored. The memory data register (MDR) is a register of a computer's control unit that contains the data to be stored in the computer storage (e. g. RAM), or the data after a fetch from the computer storage. What are the advantages and disadvantage of fixed size instructions and varying size instructions? How does the datapath hardware deal with both?

Explanation / Answer

fixed-length instructions :-
advantage:- fixed-length instruction is fast and results in better performancewhen instruction levelpipelining is used.
Diadvantage:- wastes space
b. variable-length instructions:-
Advantage:- Variable-length instruction saves storage space.
Disadvantage:- more complex to decode

datapath hardware deal with Fixed length instructions :-

Length of all instructions the same

Easier to decode single instruction in hardware

Easier to decode multiple instructions concurrently

Wasted bits in instructions

datapath hardware deal with Variable instructions :-

Length of instructions different (determined by opcode and sub-opcode)

+ Compact encoding (Why is this good?)

Intel 432: Huffman encoding (sort of). 6 to 321 bit instructions. How?

More logic to decode a single instruction

Harder to decode multiple instructions concurrently

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