CISC vs RISC

CISC vs RISC - CISC architecture reduces the number of instructions per program while increasing the number of cycles per instruction. Meanwhile, the RISC architecture reduces the cycles per instruction while increasing the number of instructions per program.

In this article, we will explore CISC vs RISC in detail. But, before we start exploring that, let’s go through the list of topics listed under the table of contents (TOC) that we will cover in this article.

Table of contents (TOC)

• CISC vs RISC
• What is CISC?
• What is RISC?
• Key differences Between CISC vs RISC
• Conclusion

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CISC vs RISC

For a better understanding, let’s go through CISC vs RISC in a tabular format:

Benchmark	CISC	RISC
Full form	Complex Instruction Set Architecture	Reduced Instruction Set Architecture
This architecture emphasizes on	Hardware	Software
Control unit used	Hardwired and microprogrammed control unit	Hardwired control unit
Types of operations that can be performed are	Register to Register, Register to Memory, and Memory to Memory	Register to Register
Size of code	Small	Large
Number of registers required	Less	More
The execution time required for an instruction	More than one clock cycle	A single clock cycle
Use of pipeline is	Difficult	Easy
Decoding instructions is	Difficult	Simple
The instruction format is	Variable	Fixed
Examples	VAX, System/360, etc.	Power Architecture, SPARC, etc.

What is CISC?

CISC Definition: CISC, or Complex Instruction Set Architecture, reduces the number of instructions per program while increasing the number of cycles per instruction.

The CISC architecture reduces the number of instructions on each program while increasing the number of cycles per instruction. Because of this functionality, the instructions can take a lot of time in order to complete their execution. In CISV architecture, the instructions are directly built into hardware as hardware is faster in comparison to the software.

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Regarding CISC vs RISC, in terms of efficient use of memory, CISV is way better than RISV, and apart from all that, CISC chips are very easy to program. Here’s the CISC architecture diagram that will help you to understand it in a better way:

What is RISC?

RISC Definition: RISC, or Reduced Instruction Set Architecture, reduces the cycles per instruction while increasing the number of instructions per program. 

The RISC architecture reduces the cycles per instruction while increasing the number of instructions per program. Because of this functionality, the instructions take much less time to complete their execution compared to the execution of the instruction in the CISC architecture. RISC architecture emphasizes on software to optimize the instruction set.

Each clock cycle, RISC-based machines execute one instruction. It should be noted that a single instruction that requires one instruction to execute on a CISC architecture may take several instructions to execute on a RISC architecture. As a result, the RISC architecture requires more RAM in comparison to the CISC architecture in order to hold values as it loads each instruction, acts on it, and then loads the next instruction. Here’s the CISC architecture diagram that will help you to understand it in a better way:

CISC vs RISC - Key Differences

Here are the key differences between CISC vs RISC:

• RISC code expansion may cause issues, whereas CISC code expansion does not.
• Instruction decoding in RISC is simple, whereas instruction decoding in CISC is complex.
• CISC uses hardwired and microprogrammed control units, but RISC only uses hardwired control units.
• In CISC, the size of the code is small, and the use of a pipeline is complex. On the other hand, in RISC, the size of the code is significant, but the use of the pipeline is easy.
• In CISC, the execution time required for an instruction is more than one clock cycle, whereas, in RISC, the execution time required for an instruction is a single clock cycle.
• CISC reduces the number of instructions per program while increasing the number of cycles per instruction. On the other hand, RISC reduces the cycles per instruction while increasing the number of instructions per program. 

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Conclusion

In terms of CISC vs RISC, the CISC architecture reduces the number of instructions per program while increasing the number of cycles per instruction. On the other hand, the RISC architecture reduces the cycles per instruction while increasing the number of instructions per program. Designing a CPU using RISC architecture is much more beneficial in comparison to CISC architecture. It is so because designing a CUP with RISC architecture is way more accessible, cheaper, and quicker.

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