Based on Word Length
Hope you read about word length above. So based on the word length of a processor we can have 8-bit, 16-bit, 32-bit and 64-bit processors.
RISC – Reduced Instruction Set Computer
RISC is a type of microprocessor architecture which uses small, general purpose and highly optimized instruction set rather than more specialized set of instructions found in others. RISC offers high performance over its opposing architecture CISC (see below). In a processor, execution of each instruction require a special circuit to load and process the data. So by reducing instructions, the processor will be using simple circuits and faster in operation.
- Simple instruction set
- Larger program
- Consists of large number of registers
- Simple processor circuitry (small number of transistors)
- More RAM usage
- Fixed length instructions
- Simple addressing modes
- Usually fixed number of clock cycles for executing one instruction
CISC – Complex Instruction Set Computer
CISC is the opposing microprocessor architecture for RISC. It is made to reduce the number of instructions per program, ignoring the number of cycles per instruction. So complex instructions are directly made into hardware making the processor complex and slower in operation.
This architecture is actually designed to reduce the cost of memory by reducing the program length.
- Complex instruction set
- Smaller program
- Less number of registers
- Complex processor circuitry (more number of transistors)
- Little RAM usage
- Variable length instructions
- Variety of addressing modes
- Variable number of clock cycles for each instructions
Special Purpose Processors
There are some processors which are designed to handle some specific functions.
- DSP – Digital Signal Processors
- Coprocessors – processors used along with a main processor (8087 math-coprocessor used with 8086)
- Input/Output processors
- Transputer – Transistor Computer : Microprocessor with its own local memory
