RISC vs CISC | RISC | Reduced Instruction Set Computer | CISC | Complex Instruction Set Computer

Summary

This video offers a comprehensive comparison between RISC (Reduced Instruction Set Computer) and CISC (Complex Instruction Set Computer) architectures. It explains the fundamental differences in instruction set size, instruction fetch time, and design philosophy. The video clarifies that RISC has a fixed, smaller set of instructions leading to simpler and faster execution, whereas CISC features a larger, more complex set allowing for more compact code. It also touches on aspects like addressing modes, the number of registers, compiler design, and the suitability of each architecture for specific types of operations, concluding with the advantages and disadvantages of both.

Takeaways

• 😀 RISC stands for Reduced Instruction Set Computer and CISC for Complex Instruction Set Computer, highlighting the fundamental difference in the number and complexity of instructions.
• 🔍 RISC has a fixed instruction size, whereas CISC's instruction size varies based on the complexity of the instruction.
• ⏱ In RISC, the instruction fetch time is consistent for all instructions, while in CISC, it varies depending on the instruction's complexity.
• 📚 RISC has a smaller and simpler instruction set compared to CISC, which has a larger and more complex set with a variety of instructions.
• 🔄 RISC is based primarily on register-to-register operations, while CISC includes a wider range of memory-based instructions.
• 📏 RISC has fewer addressing modes due to its focus on register operations, whereas CISC offers more modes due to its memory-based instructions.
• 💪 RISC has more registers within the CPU, as it relies heavily on register-to-register operations, while CISC has fewer due to its reliance on complex instructions.
• 🛠️ Compiler design is simpler for RISC due to its smaller and simpler instruction set, whereas it's more complex for CISC due to its larger and more complex set.
• 📈 RISC results in longer program sizes because simple instructions require more steps to perform tasks, while CISC has shorter programs due to the availability of complex instructions.
• 🔢 The number of operands in RISC is fixed, mainly involving registers, while in CISC, the number of operands varies with the instruction, involving both registers and memory.
• 🔧 RISC uses a hardware control unit due to its fixed and simple instruction set, making it faster, while CISC often uses micro-programmed control units due to the complexity of its instructions.
• 🚀 Execution speed is generally faster in RISC due to efficient pipelining facilitated by fixed instruction size, whereas CISC faces inefficiencies due to variable instruction size and the need for frequent pipeline flushes.

Q & A

What does RISC stand for in computer architecture?

RISC stands for Reduced Instruction Set Computer. It is a design approach that uses a smaller set of simple instructions with a fixed instruction size.

What is the full form of CISC in the context of computer design?

CISC stands for Complex Instruction Set Computer. It features a larger set of complex instructions with varying instruction sizes.

Why is the instruction size fixed in RISC architecture?

The instruction size is fixed in RISC architecture to simplify the design and improve the efficiency of instruction fetching and pipelining.

How does the instruction fetch time differ between RISC and CISC architectures?

In RISC, the instruction fetch time is constant for all instructions due to the fixed instruction size. In CISC, the fetch time varies depending on the complexity of the instruction.

What is the typical size and complexity of the instruction set in RISC and CISC architectures?

The instruction set in RISC is small and simple, while in CISC it is large and complex, with a variety of instructions available.

How does the number of addressing modes compare between RISC and CISC architectures?

RISC architecture has fewer addressing modes, mostly because most instructions are based on registers. CISC, on the other hand, has more addressing modes due to its complexity and variety of instructions involving both registers and memory.

Why does RISC architecture have more registers in the CPU?

RISC architecture has more registers because it relies heavily on register-to-register operations, which simplifies the design and execution of instructions.

What is the typical complexity of compiler design for RISC and CISC architectures?

Compiler design is simpler for RISC due to its small and simple instruction set. For CISC, compiler design is more complex due to the large and complex instruction set and the variety of addressing modes.

Why is the program size typically longer in RISC architecture compared to CISC?

The program size is longer in RISC because its simple instructions require more steps to perform complex tasks, whereas CISC can perform the same tasks with fewer, more complex instructions.

How does the number of operands in instructions differ between RISC and CISC architectures?

In RISC, the number of operands is typically fixed, often involving registers and memory. In CISC, the number of operands can vary depending on the instruction, which can involve a mix of registers and memory.

What is the typical control unit design for RISC and CISC architectures?

RISC typically uses a hardware control unit due to its fixed and simple instruction set, which allows for direct execution. CISC often uses a micro-program-controlled unit due to the complexity of its instruction set, which requires more elaborate control mechanisms.

Why is execution speed generally faster in RISC compared to CISC?

Execution speed is faster in RISC because of the uniform instruction size, which allows for efficient pipelining. In CISC, the variable instruction size can lead to inefficient pipelining and the need to flush the pipeline more frequently, slowing down execution.

Which type of operations are RISC and CISC architectures more suitable for?

RISC is more suitable for dedicated operations due to its fixed and simple instructions, while CISC is more suitable for a variety of operations due to its complex instructions that can handle different tasks more efficiently.