A microprocessor is the controlling unit of a computer made up of a small chip capable of operations and communication purposes. This small chip is known as the CPU which is microprocessors. It consists of ALU, Control Unit, and registers. This works on the instruction set and the cycle of processing. They are classified as:
- Complex Instruction Set Computer (CISC)
- Reduced Instruction Set Computer (RISC)
Complex Instruction Set Computer (CISC)
CISC chips have a larger set of complex instructions. This needs multiple numbers of instruction cycles for execution. It works on the fetch and execution cycle which is a combination of a register to register transfer functions. It has the ability to execute addressing modes or multi-step operations within one instruction set. The CISC memory reads and writes operations from the integral part for execution. Because of frequent memory references, there is a reduction in the speed of the CISC machine.
Earlier, the CISC machine did not have the concept of pipelining. It has a variable-length instruction format. For general purpose, where the speed of the processors is not the primary importance, there is the use of CISC machines because of their low cost and affordability.
Advantages:
- They are less expensive than hardwiring a control unit and also are easy to implement.
- Only fewer instructions are needed to accomplish the execution of a program.
- It does not make the compiler complicated.
Disadvantages:
- The chip hardware is complex to use.
- However, there is a need for only fewer instructions, they are longer and take more time for execution.
Reduced Instruction Set Computer (RISC)
They are also the microprocessors designed to perform instructions at a higher speed. The CISC used complex assembly language instructions, which slowed down the compiler so RISC was evolved. So this contains simper instructions due to which RISC requires less no. of transistors. These are short and simple so it can be executed in a single instruction cycle. RISC cuts down on the number and complexity of instructions so that each one can be accessed and executed faster, and fewer semiconductors are required to process them.
There is no micro-program in RISC for interpreting the instructions. It has an efficient instruction pipeline. As soon as it completes one stage of the cycle, it proceeds with the second stage. That is why; it is called functioning in a pipeline manner. By overlapping the execution, RISC achieves execution parallelism.
Advantages:
- The execution time is faster than CISC.
- It does not require complex hardware.
- It uses fewer instructions per task.
Disadvantages:
- The instruction schedule makes debugging difficult.
- It requires large memory caches to feed instructions.
- Intermixing of machine language makes it hard to read.
RISC vs. CISC
Pipelining
Pipelining improves instruction execution speed by putting the execution steps into parallel. A CPU can receive a single instruction, begin executing it, and receive another instruction before it has completed the first. This allows for more instructions to be performed, about, one instruction per clock cycle.
Parallel Processing
Parallel processing is the simultaneous execution of instructions from the same program on different processors. A program is divided into multiple processes that are handled in parallel in order to reduce execution time.
