For human assembly programmers, which type of CISC or RISC processors are easy f
ID: 3869541 • Letter: F
Question
For human assembly programmers, which type of CISC or RISC processors are easy for programming (assembly programming)? Why (justify your choice)? Suppose we compile source code files in high-level programming languages (e.g., C/C-Java, and etc.), which type of CISC or RISC instruction set architecture will result binary executable with a larger number of instructions? Why? Which types of processors (CISC or RISC processors) do compilers have more opportunities to perform compile-time optimizations? Justify you choice.Explanation / Answer
Question1:
RISC processors typically have fewer and simpler instructions that in most cases take up one single word. You will not find time saving instructions like the x86’s REP MOVSD on a RISC processor. The trade off is that RISC processors are made with combinatorial logic and execute most instructions in a single clock cycle, whereas CISC processors often use embedded microcode to execute complex instructions and need extra clock cycles. So while RISC requires more instructions for many jobs, they typically get the job done more quickly.
A RISC instruction set will be quite basic. Some of the instructions you take for granted may not be present - the RISC AVR, for example, doesn’t have an add-immediate instruction, so to add 5 to a register, you have to tell it to subtract-immediate minus 5. The reason is that there are only so many bits in an instruction word (16 in the AVR’s case) and since they wanted every instruction to take up only one word, some hard decisions needed to be made about which ones to include and which could be worked around. This was less of a problem with processors like the ARM, where the instruction word has 32 bits allowing a great deal more flexibility.
CISC [Complex instruction set Computing]
1. Very large instruction sets reaching up to and above three hundred seperate instructions.
2. Performance was improved by allowing the simplification of program compilers, as the range of more advanced instructions available led to less refinements having to be made at the compilation process. However, the complexity of the processor hardware and architecture that resulted can cause such chips to be difficult to understand and program for, and also means they can be expensive to produce.
3. More specialized addressing modes and registers also being implemented, with variable length instruction codes.
4. Instruction pipelining can not be implemented easily.
5. Many complex instructions can access memory, such as direct addition between data in two memory locations.
6. Mainly used in normal PC’s, Workstations and servers .
7. CISC systems shorten execution time by reducing the
number of instructions per program.
8. Examples of CISC Processors: Intel x86.
RISC [Reduced instruction set Computing]
1. Small set of instructions.
2. simplified and reduced instruction set, numbering one hundred instructions or less. because of simple instructions, RISC chips requires fewer transistors to produce processors. Also the reduced instruction set means that the processor can execute the instructions more quickly, potentially allowing for greater speeds. However, only allowing such simple instructions means a greater burden is placed upon the software itself. Less instructions in the instruction set means a greater emphasis on the efficient writing of software with the instructions that are available.
3. Addressing modes are simplified back to four or less, and the length of the codes is fixed in order to allow standardization across the instruction set.
4. Instruction pipelining can be implemented easily.
5. Only LOAD/STORE instructions can access memory.
6. Mainly used for real time applications.
7. RISC systems shorten execution time by reducing the clock
cycles per instruction (i.e. simple instructions take less time
to interpret).
8. Examples of RISC Processors: Atmel AVR, PIC, ARM
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