Microprocessor Architecture: CISC vs RISC and Performance Metrics

Microprocessors: Core Concepts

A microprocessor is a component that incorporates all the functions of a CPU onto a single integrated circuit.

Technological Characteristics

• Instruction Set: The specific commands the processor can execute.
• Word Size: The number of bits processed in a single operation.
• Clock Speed: The frequency at which the processor operates.
• Pipelining: Processing instructions like an assembly line.
• Bus Width: The data path width for instruction and data transfer.

Processor Architecture Definitions

• Instruction sets and addressing modes.
• Organization of functional units.
• Electronic component technology.

CISC (Complex Instruction Set Computer)

• Extensive Instruction Sets: Features variable-length instruction formats with varying numbers of fields.
• Microprogrammed Control Unit: Complex electronic design due to the high volume of instructions.

RISC (Reduced Instruction Set Computer)

• Simplified Instruction Set: Uses simpler electronics, making it easier to increase operating frequency.
• Compiler Reliance: The lack of complex hardware functionality is resolved by compilers using sequences of simple instructions.

Performance Metrics

• MHz/GHz: Represents the number of processor cycles executed per second.
• MIPS: Million instructions per second.
• FLOPS: Floating-point operations per second.

External Bus (FSB) and Speed

The Front Side Bus (FSB) is the speed at which the CPU communicates with the motherboard. The internal CPU speed is calculated by multiplying the external bus speed by a multiplier factor, which must be supported by the motherboard.

Cache Memory (SRAM)

Cache is a high-speed SRAM memory that accelerates data transfer between the CPU and RAM. It stores frequently needed data and instructions to minimize latency.

Cache Hierarchy

• Level 1 (L1) Cache: Located within the processor core; extremely fast but limited in size.
• Level 2 (L2) Cache: Larger capacity, slightly slower than L1.

The system searches for data in the cache first, then moves to RAM, and finally to the hard disk if necessary.