Classification of Microprocessor based on Characteristics

A Microprocessor can be classified depending on many measure here we discuss classification of microprocessor based on characteristics.

The microprocessors are classified into three categories. These are as follows:

Classification of microprocessor

  1. RISC processors
  2. CISC processors
  3. Special processors.
19-Classification of Microprocessor based on Characteristics

Classification of Microprocessor

RISC Processors

RISC is an acronym for reduced instruction set computer. The concept of RISC processor involves an attempt to reduce execution time by simplifying the instruction set of the computer.

The major characteristics of a RISC processors are:

  • Relatively few instructions
  • Relatively few addressing modes    
  • Memory access limited to load and store instructions
  • All operations done within the registers of the CPU
  • All operations done within the registers of the CPU
  • Fixed-length, easily decoded instruction format
  • Single-cycle instruction execution
  • Hardwired rather than microprogrammed control.

Some architectural features of RISCs are:

  • Relatively large number of registers in the processing unit
  • Use of overlapped register windows to speedup procedure, call and return
  • Efficient instruction pipeline
  • Compiler support for efficient translation of high level language programs into machine language programs.

Some popular RISC processors are:

  • Power PC: 601, 604, 615, 620
  • DEC Alpha: 210642, 211066, 21068, 21164
  • MIPS: TS (R10000) RISC Processor
  • PA-RISC: HP 7100LC

CISC Processor

CISC is an acronym for complex instruction set computer. Major characteristics of a CISC processors are:

  • Large number of instruction
  • Some instructions that perform specialized tasks
  • Variety of addressing modes
  • Variable length instruction formats
  • Instructions that manipulate control
  • Several cycles may be required to execute one instruction.

Examples: Intel’s x86 family: Motorola’s 680000, 68020, 68030, 68030, 68040 etc.

For many years. Intel is the only major supplier of x86 processor with a few authorized and controlled alternate sources. Today a large number of companies offer compatible processors with no assistance from Intel. They are:

  • AMD (Advanced Micro Device) processors
  • Cyrix processors
  • Texas instrument (TI) processors
  • NexGen processors.

All CISC microprocessors that run PC software were derived from the early Intel 8086 or x86 architecture. Today Intel controls the development of CISC microprocessor and other industries produce the Intel compatible processors.

Intel presented a new processor in 1993 called Pentium. With this processor, Intel opened a new era of technology. Day by day, new features are added to the processor and as a result new highly developed processors come out. Some of them are:

PentiumPro: This is an optimized processor for high-performance network server implementation.

Pentium III: This is the recent Intel processor in the market, which has both the technology of pentiumPro and also MMX (multimedia extension) technology. The new PIII system gives very good combination of price and performance and graphic applications.

Special Processors

There are several other processors, which are used for special purposes. Some of these processors are briefly discussed below.

Coprocessor

A coprocessor is a microprocessor but unlike a general propose microprocessor, it is dedicated to its specific function as a purpose device.

Because, the coprocessor is designed for a specific purpose, it can handle its particular function many times faster that the ordinary general purpose, it can handle its particular function many times faster than the ordinary general purpose microprocessor. The most well know coprocessor is the math-coprocessor.

Until the introduction of the 486DX microprocessor, the math-coprocessor was a separate chip. But 486DX and Pentium microprocessors have the math-coprocessor integrated on the same chip with the microprocessor. Intel math-coprocessors are:

  • 8087-used with 8086
  • 80287-used with 80286
  • 80387-used with 80386.

Cyrix and Weitek also market math-coprocessors.

Input / Output processor

One of the most important type of processors in I/O processors. An I/O processor has a local memory of its own right. With this architecture, a large set of I/O devices can be controlled, with minimal CPU involvement.

A common use for such architecture has been to control communication with interactive terminals. The I/O processors take care of most of the tasks involved in controlling the terminals. I/O processors are used in the following fashion:

  • The CPU executes a series of data-transfer instructions that send a set of input operands and command information to registers in the I/O processor.
  • The I/O processor decodes and executes the command received from the CPU generating a result that is placed in registers accessible to the CPU.
  • The CPU determines that the I/O processor has completed its task either by checking its status or else by receiving an interrupt signal from the I/O processor.
  • The CPU then obtains the results from the I/O processor by executing more data transfer instructions.

Common examples of I/O processors are:

  • DMA (direct Memory Access) controller
  • Keyboard/mouse controller
  • Graphic display controller
  • SCSI port controller etc.

Transputer

The transputer (transistor computer) is a high performance microprocessor designed to facilitate inter-process and inter-processor  communications and is targeted at the efficient exploitation of very large scale intergration (VLSI) technology.

The most important feature of the transputer is its external links, which enable it to be used as a building block in the construction of low cost, high performance multiprocessing systems.

Communication takes place (via these links) only between pairs of devices and is distributed throughout the system. The transporter family consists of several types of VLSI devices including the 16-bit T212, the 32-bit T425 and the floating point T800, T805 and T9000 processors.

DSP (Digital Signal Processor)

This processor is specially designed to handle real-world analog signals that have been converted to digital representations. Some of the applications that DSP can support are:

  • Sound and music synthesis
  • Modem function
  • Audio and video compression
  • Speech synthesis and decompression
  • Speech recognition
  • Video signal processing
  • 2D and 3d graphics acceleration.

Examples: Texas Instrument’s TMS 320 series, e.g., TMS 320C40, TMS320C50.

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