Difference between RISC and CISC Processor | Set 2

The microprocessor is a processing unit on the single chip. It is the integrated circuit that performs the core functions of the computer CPU. It is the multipurpose programmable silicon chip constructed using a Metal Oxide Semiconductor (MOS) technology which is clock driven and register based. It accepts a binary data as a input and provides output after processing it as per a specification of instructions stored in a memory. These microprocessors are capable of the processing the 128 bits at the time at the speed of a one billion instructions per second.

Characteristics of a Microprocessor

1. Instruction Set : The set of complete instructions that the microprocessor executes is termed the instruction set.

2. Word Length : The number of bits processed in a single instruction is called word length or word size. The Greater the word size is the larger the processing power of the CPU.

3. System Clock Speed : A Clock speed determines how fast the single instruction can be executed in the processor. The microprocessor is controlled by the System Clock. A Clock speeds are generally measured in the millions of a cycles per second (MHz) and thousand million cycles per second GHz. A Clock speed is considered to be the very important aspect of predicting a performance of the processor.

What is Reduced Instruction Set Computer(RISC)?

It stands for Reduced Instruction Set Computer. It is a type of microprocessor architecture that uses a small set of instructions of uniform length. These are simple instructions that are generally executed in one clock cycle. RISC chips are relatively simple to design and inexpensive. The setback of this design is that the computer has to repeatedly perform simple operations to execute a larger program having a large number of processing operations. 
Examples: SPARC, POWER PC, etc.

Advantages of Reduced Instruction Set Computer (RISC)

• Faster execution speed RISC processors use the simpler instructions that can be executed more quickly leading to improved overall performance in the many tasks.

• Lower power consumption The simpler design of a RISC processors often results in the lower power usage making them the ideal for mobile devices and energy efficient computing.

• Easier to design and manufacture RISC processors have a simpler architecture which can make them the easier and potentially cheaper to design and produce.

Disadvantages of Reduced Instruction Set Computer (RISC)

• Larger code size RISC processors often require more lines of code to perform complex tasks, which can lead to larger program sizes and increased memory usage.

• More work for compilers The simpler instruction set means compilers for RISC processors need to do more work to translate high-level programming languages into machine code.

• Limited built-in functionality RISC processors have fewer complex instructions built into hardware, which can make certain specialized tasks less efficient without additional software support.

What is Complex Instruction Set Computer (CISC)?

It stands for Complex Instruction Set Computer. These processors offer the users, hundreds of instructions of variable sizes. CISC architecture includes a complete set of special-purpose circuits that carry out these instructions at a very high speed. These instructions interact with memory by using complex addressing modes. CISC processors reduce the program size and hence lesser number of memory cycles are required to execute the programs. This increases the overall speed of execution. 
Examples: Intel architecture, AMD

Advantages of Complex Instruction Set Computer (CISC)

• Smaller code size CISC processors can perform complex operations with single instructions, often resulting in more compact code and reduced memory usage.

• Rich instruction set The diverse set of complex instructions can make programming easier and more intuitive for certain tasks, especially in assembly language.

• Backwards compatibility CISC architectures, like x86, often maintain compatibility with older software, making system upgrades easier for users and businesses.

Disadvantages of Complex Instruction Set Computer (CISC)

• Slower execution speed Complex instructions typically take longer to execute, potentially resulting in slower overall performance compared to RISC processors.

• Higher power consumption The more complex hardware required for the CISC processors often leads to a increased power usage making them less suitable for the mobile devices.

• More complex hardware design a CISC processors require more complex circuitry to handle their varied the instructions which can make them a more challenging and expensive to design and manufacture.

What is EPIC?

It stands for Explicitly Parallel Instruction Computing. The best features of RISC and CISC processors are combined in the architecture. It implements parallel processing of instructions rather than using fixed-length instructions. The working of EPIC processors is supported by using a set of complex instructions that contain both basic instructions as well as the information of execution of parallel instructions. It substantially increases the efficiency of these processors.

Difference between RISC and CISC processor

Refer for Set-1: RISC and CISC

Conclusion

The Reduced Instruction Set Computing and a Complex Instruction Set Computing are the method of a processor design. The RISC processors use the fewer and simpler instructions that execute quickly while the CISC processors have the complex instructions that can perform the multiple operations. The RISC focuses on a efficiency and speed using a simpler hardware and relying on the software. CISC aims for a versatility with more built in functionality in the hardware. RISC is a generally faster and more energy efficient while a CISC can be more compact in a terms of code size.