Why did CISC processors (x86) historically gain popularity first, and RISC only now gaining momentum?

Historically, CISC processors (e.g., x86) became widespread due to backward compatibility and a more complex instruction set, which allowed complex operations to be performed with a single instruction. This simplified compilation and programming in the early stages of computer development.

RISC processors, on the other hand, have a simpler and more uniform instruction set, which allows for optimized execution and increased performance through simplified architecture and pipelining.

Reasons for the initial popularity of CISC:

• Compatibility with existing software and architecture.
• Developed ecosystem and manufacturer support.
• More complex instructions made programming easier during the era of limited compilers.

Why RISC is gaining momentum now:

• Modern compilers better optimize code for simple instructions.
• RISC architectures (e.g., ARM) are more energy-efficient, which is important for mobile devices.
• Growing popularity of embedded systems and mobile platforms.
• Open architectures (RISC-V) stimulate innovation and reduce costs.

Thus, the paradigm shift is driven by technological development, energy efficiency requirements, and market changes.