• The term “Microprocessor” was first used when the Viatron system 21 small Computer System was announced in 1968. Since the 1970s, the use of microprocessors has consequently increased, cutting across several use cases.
  • Microprocessors were initially called “Microcomputer on a chip” until 1972.
  • The microprocessor was invented by a team of silicon engineers and logic architects: Marcian (Ted) Hoff, Masatoshi Shima, Federico Faggin, and Stanley Mazor in jan 1971.
  •  The first commercial product to use a 4004 microprocessor was the Busicom calculator 141-PF.
  • Generation of Microprocessor : 
    • 1st Generation Microprocessors(1971-1973) :
      • In 1971, INTEL created the first microprocessor 4004 is 4-bit microprocessors that would run at a clock speed of 740 kHz, designed by Federico Faggin.
      • During this period, the other microprocessors in the market including Rockwell international PPS-4 and National semiconductors IMP-16 were in use. But, all these were not stable/compatible processors.
    • 2nd Generation Microprocessors(1974-1978) 

      • This generation has very efficient and 8-bit microprocessors were implemented like Motorola 6800 and 6801, INTEL- 8008(not stable), 8080, 8085, and Zilog’s-Z80, which were among the most popular ones.
      • They were super fast speed and costly as they were based on NMOS (N-type Metal Oxide Semiconductor) technology fabrication.
    • 3rd Generation Microprocessors(1979-1980): 

      • This was 16-bit processors designed using HMOS(High Metal Oxide Semiconductor) technology.
      • The first multi-chip 16-bit microprocessor was the National Semiconductor IMP-16, introduced in early 1973.
      • In late 1973, National Semiconductor introduced the first 16-bit single-chip microprocessor, the PACE, followed by an NMOS version, the INS8900.
      • The 3rd generation microprocessor were INTEL 8086/80186/80286 and Motorola 68000 and 68010 were developed.
      • The speeds of those processors were four times better than the 2nd generation processors.
    • 4th Generation Microprocessors(1981-1985): 

      • This was 32-bit microprocessors designed using HCMOS(High-speed CMOS[Complementary Metal Oxide Semiconductor]) fabrication.
      • The world’s first single-chip fully-32-bit microprocessor, featuring 32-bit data paths, 32-bit buses, and 32-bit addresses, was the AT&T Bell Labs BELLMAC-32A, with first samples in 1980 and general production in 1982.
      • The 4th generation microprocessor were INTEL- 80386 and Motorola’s 68020/68030 were the popular processors.
    • 5th Generation Microprocessors(1986- ): 

      • This was 64-bit microprocessors.
      • This generation has been bringing out high-performance and high-speed processors.
      • Example of 5th generation processors include Pentium, Celeron, Dual and Quad-core processors.
  • Intel’s Microprocessors :
    • Pentium:
      • Pentium was introduced on March 2, 1993.
      • This processor’s name was derived from the Greek word Penta, which means five.
      • Pentium refers to Intel’s single-core x 86 microprocessor.
      • March 20,2000: Intel Pentium III processor (866, 850MHz) came into existence.
      • Nov 20,2000: Intel Pentium 4 Processor (1.50, 1.40GHz) came into existence.
      • April 2, 2002: Intel Pentium 4 Processor (2.40, 2.20 GHz) came into existence.
      • In 2005,Intel Pentium 4 Processor came into existence with Extreme Edition supporting HT Technology (3.80GHz).
    • Intel Celeron & Core 2 Duo:
      • Intel Celeron was introduced in April 1998.
      • It refers to a range of Intel’s X86 CPUs for value PCs.
      • It is based on Pentium 2 and can run on all IA-32 computer programs.
      • On 2nd March 2008, the Core 2 Duo processor like E4700 was released by Intel.
    • Xeon
      • Xeon processor is a 400 MHz Pentium processor from Intel for use in workstations and enterprise servers.
      • This processor is designed for multimedia applications, engineering graphics, the Internet, and large database servers.
      • Jan 12, 2001: Intel Pentium III Xeon Processor (800 MegaHertz) introduced.
      • March 2, 2004: Intel Xeon Processor MP 3 GHz (4 MB L3 CACHE) introduced.
      • October 2005: Dual-Core Intel Xeon Processor (2.8 Giga Hertz) introduced.
    • Core i Series:
      • The first Core i3 desktop processors like the i3-530 were released by Intel on Jan 7, 2010.
      • The first Core i5 desktop processor including four cores like the i5-750 on Sept 8, 2009, was released by Intel. 
      • The first Core i7 mobile processor like i7-720QM was released in Sep 2009 by Intel.
      • The first desktop Core i9 processor like the i9-7900X was released in June 2017.
  • Motorola Microprocessor:
      • Motorola Inc from Japan is one of the leading manufacturer of Motorola microprocessors.

      • These processors are used in all types of Apple Macintosh Computers till the year 1990 in different workstations.
      • The 8-bit microprocessor like 6800 was released by Motorola after the Intel 8080 in the year 1974.
      • The Motorola 6800 microprocessor was released in the year 1974.
      • The Motorola 68000 microprocessor was released in the year 1979.
      • The Motorola power PC 603 microprocessor was released in the year 1994.


  • A digital computer with one microprocessor which acts as a CPU is called microcomputer.
  • It’s often known simply as a processor, a central processing unit, or as a logic chip.
  • MicroController: The microcontroller puts the central processing unit and other peripherals onto the same chip to function. The microcontroller consists of a single-chip housing a more powerful CPU; this chip also connects to other external peripherals.


Instruction Set: These are sets/group of related commands understandable by the microprocessor. The instruction set is typically an interface between the computer software and hardware.

Clock Speed/Rate: This is the number of operations a microprocessor can perform in a second, expressed in Hertz or its multiples. 

IPC: (Instruction Per Cycle) IPC measures the volume of instructions a computer’s central processing unit can execute in a single clock.

Bandwidth: This is the number of bits the microprocessor can process in a single instruction.

Bus: These are conductors used to transmit data, control signal, or address information in different microprocessor elements. Generally, there are three (3) basic types of buses, address bus, data bus, and control bus.


    • A timer is a specialized type of clock which is used to measure time intervals of a process/task.
    • Timers are usually also counters.
    • In Timer, the register value is incremented each time for every machine cycle.
    • A timer uses the frequency of the internal clock, and generates delay.
    • A timer may counts from zero to upwards or counts down from a specified time interval for measuring time elapsed.


  • A complete processor when made on a single silicon chip is called Microprocessor.
  • In another words, Computer’s Central Processing Unit (CPU) when built on a single Integrated Circuit (IC) is called a microprocessor.
  • The microprocessor is a multipurpose, programmable, clock-driven, register-based, digital integrated circuit or electronic device that accepts binary data as input, processes it according to the available instructions stored in its memory, and provides related results in binary form as output.
  • A microprocessor is a CPU that consists of multiple integrated circuits containing logic, control, and arithmetic circuitry needed for a typical CPU to function correctly.


  • A microprocessor is a Micro computer processor where the data processing logic and control is included on a single integrated circuit Chip, or a small number of integrated circuits.
  • General-purpose type of microprocessors in personal computers are used for computation, text editing, multimedia display, and communication over the Internet. 
  • Microprocessors are smaller, faster, relatively less costly than integrated circuits.
  • The significant difference between a microprocessor and an integrated circuit is that while an integrated circuit controls the flow of protons, a microprocessor controls the flow of electrons.
  • Examples of microprocessors include Intel 386, Pentium Pro, Intel 486, etc.


    • Microprocessors are made from quartz, metals, silicon, and other chemicals.
    • The microprocessor consists of the arithmetic, logic, and control circuitry with several registers and all are required to perform the functions of a computer’s central processing unit.
    • The microprocessor contains millions of tiny components like transistors, registers, diodes etc. which are combined/fabricated on ICs using VLSI technology to work together.
    • Microprocessors contain both combinational logic circuit and sequential digital logic circuit, and operate on numbers and symbols represented in the binary number.
    • Integrated circuit processors are produced in large numbers by highly automated metal-oxide-semiconductor(MOS) fabrication processes, resulting in a relatively low unit price.
    • Working Mechanism: Technically, at first, the microprocessor sequentially stores inputs as instructions in the computer’s storage memory. Afterward, it fetches the stored instructions and decodes them. The decoded instructions are then executed until the microprocessor meets a STOP instruction. Finally, the results are sent in binary form as output via the output port after execution.


    • A microprocessor can be classified into three categories −
      • RISC Processors
      • CISC Processors
      • Special Processors

    (A) RISC Processor

      • RISC stands for ‘Reduced Instruction Set Computer’.
      • Features:
        • It consists of simple instruction/ Instruction sets.
        • It has fixed length instructions.
        • It supports different data-type formats.
        • It uses simple addressing modes/addressing schemes.
        • It has one cycle execution time.
        • It consists of a larger number of registers.
        • It consists of less number of transistors.
      • This processor is designed to reduce the execution time by simplifying the instruction set of the computer.
      • RISC microprocessor architecture uses highly-optimized set of instructions.
      • Using RISC processors, each instruction requires only one clock cycle to execute the process hence gives the uniform execution time.
      • This processor reduces the efficiency as there are more lines of code, hence more RAM is needed to store the instructions. The compiler also has to work more to convert high-level language instructions into machine code.
      • Examples of some common RISC processors are –
        • Power PC: 601, 604, 615, 620
        • DEC Alpha: 210642, 211066, 21068, 21164
        • TS (R10000) RISC Processor
        • HP 7100LC

    (B) CISC Processor

      • CISC stands for ‘Complex Instruction Set Computer’.
      • Features/Characteristics:
        • It has a wide variety of addressing modes/addressing schemes.
        • It has a larger number of instructions/instruction sets.
        • It has a variable length of instruction formats.
        • Several cycles may be required to execute/complete one instruction.
        • Instruction-decoding logic is complex.
        • One instruction is required to support multiple addressing modes.
      • This processor is designed to minimize the number of instructions per program, ignoring the number of cycles per instruction.
      • The length of the code in this processor is relatively short, so very little RAM is required to store the instructions.
      • Its architecture is designed to decrease the memory cost because more storage is needed in larger programs resulting in higher memory cost. To resolve this, the number of instructions per program can be reduced by embedding the number of operations in a single instruction.
      • Some common  example of the CISC Processors are −
        • IBM 370/168
        • VAX 11/780
        • Intel 80486

    (C) Special Processor

      • These are the processors which are designed for some special purposes.
      • These are actually a small processor having comparatively less power than main processor. 
      • The common special processors are  −
        • Co-Processor
        • Input-Output Processor
        • Transputer
        • Digital Signal Processor(DSP)

    (i) Co-Processors

        • A coprocessor is a specially designed microprocessor, which can handle its specific function.
        • Co-processors are supporting, separate, small processors works under/with main processor to speed up the processing.
        • It has many times faster than the original microprocessor.
        • It performs the job seperately but under the supervision of main processor.
        • The data transfer instructions must be specific instructions in the CPU. This type of connection is called Loosely Coupled.
        • When the arithmetic processor has a register and instruction set which can be considered an extension of the CPU registers and instruction set, then it is called a Tightly Coupled processor. Here the CPU reserves a special subset of code for arithmetic processor. In such a system the instructions meant for arithmetic processor are fetched by CPU and decoded jointly by CPU and the arithmetic processor, and finally executed by arithmetic processor. Thus, these processors can be considered a logical extension of the CPU. Such attached arithmetic processors are termed as Co-Processors.
        • The concept of co-processor existed in the 8086 machine till Intel 486 machines where co-processor was separate. However, Pentium at present does not have a separate co-processor.
        • For example – Math/Arithmetic Co-processor. Some Intel math-coprocessors are −
          • Math Co-processor 8087 – used with 8086 processor.
          • Math Co-processor 80287 – used with 80286 processor.
          • Math Co-processor 80387 – used with 80386 processor
            Arithmetic/Math Co-Processors :
            • Arithemetic processors is a separate and specific type of hardware/processor(single IC) works with main processor (but freely) to perform some special controlling and data processing jobs for implementing non-arithmetic functions.
            • The cost and complexity of this processor is comparatively less than when built with main processor.
            • It is a special purpose arithmetic processor, for performing only the arithmetic operations.
            • This processor can be utilized by the CPU to execute complex arithmetic instructions. In the absence of arithmetic processors in a CPU, these instructions may be executed using the slower software routines by the CPU itself. Thus, this auxiliary processor enhances the speed of execution of programs/computer having a lot of complex arithmetic computations.
            • An arithmetic processor also helps in reducing program complexity, as it provides a richer instruction set for a machine. Some of the instructions that can be assigned to arithmetic processors can be related to the addition, subtraction, multiplication, and division of floating point numbers, exponentiation, logarithms and other trigonometric functions.

        (ii) Input-Output/Peripheral Processor

            • It is a specially designed microprocessor having its own local memory, which is used to control I/O devices with minimum CPU involvement.
            • A processor is treated as one of the Input / Output or peripheral units then it is termed as a Peripheral Processor.
            • The CPU sends data and instructions to the peripheral processor, which performs the required operations on the data and communicates the results back to the CPU.
            • A peripheral processor has several registers to communicate with the CPU. These registers may be addressed by the CPU as Input /Output register addresses.
            • The CPU and peripheral processors are normally quite independent and communicate with each other by exchange of information using data transfer instructions.
            • Peripheral processors are not found as arithmetic processors in general. However, many chips are used for specialized I/O architecture. 
            • For example −
              • DMA (Direct Memory Access) Controller
              • Keyboard/Mouse Controller
              • Graphic/Video Display Controller(VDC)
              • SCSI Port Controller
        DMA/DMA Controller(DMAC)
              • DMA Controller is a separate hardware component of a modern computer system that allows I/O devices to directly access memory for transferring/sharing data with less participation of the main processor. 
              • Direct Memory Access involves transfer of data between I/O devices and memory by an external circuitry system called DMA controller without involving the microprocessor. However, microprocessor itself initiates the DMA control process by providing starting address, size of data block and direction of data flow.
              • The DMA controller notifies the Digital Siganl Processor(DSP) that it is ready for a transfer.
              • DMA contains a control unit to deals with the control functions during DMA operations such as read, write and interrupt.
              • DMA controller uses the same old circuits of an interface to communicate with the CPU and Input/Output devices.
              • Working Mechanism:
                i) For DMA operation to occur, the DMA controller first make a bus request (BR) by sending a control signal HOLD to the control line.
                ii) On receiving the BR through HOLD pin high, the microprocessor completes the current instruction execution and afterward it generates HLDA control signal and sends it to the DMA-Controller. This event switches over the control from microprocessor to DMA Controller. The microprocessor gets idle.
                iii) As soon as DMA controller receives HLDA (Hold Acknowledged) through Bus Grant (BG) line, it takes the control of system bus and start transferring the data blocks between memory and Input / Output devices, without involving the microprocessor.
                iv) On completion of data transfer, the DMA controller sends a low signal to the HOLD pin and hence microprocessor makes the HLDA pin low and takes the control over system bus.
              • DMA Operation Modes:
                The DMA Controller operates under three modes:
                (a) Burst Mode: Here, DMA controller switch over the control to the microprocessor only on completion of entire data transfer, irrespective of microprocessor requiring the bus. Microprocessor has to be idle during the data transfer.
                (b) Cycle-Stealing Mode: Here, DMA controller relinquish the control to microprocessor on transfer of every byte, thereby microprocessor gets the control and become able to process highly prioritized instruction. DMA need to make the BG request for each byte.
                (c)Transparent Mode: In this mode, DMA controller can transfer data blocks only when microprocessor are executing such instruction that does not requires system bus utilization.
              • Advantages:
                • Transferring the data without the involvement of the main processor will speed up the read-write task. Thus, DMA reduces the clock cycle requires to read or write a block of data.
                • DMA also reduces the overhead of the main processor and hence improves the overall performance of the system.
              • Disadvantages:
                • DMA controller steals execution cycles from the processor.
                • A final control is depends on main processor.
                • Synchronization mechanisms must be required to avoid accessing non-updated information from RAM.
        Graphic/Video Display Controller(VDC)
              • It is also called a display engine or display interface.
              • VDC is an integrated circuit and is the main component in a video-signal generator,(a device responsible for the production of a TV video signal in a computing or game system).
              • VDC is responsible for generating/controlling the timing of video signals such as the horizontal and vertical synchronization signals.
              • VDCs were earlier used in the home computers of the 1980s and also in some early video picture systems.
              • The typical example of video display processor is the VDP2 of the Sega Saturn(home video game console) and the Lisa Graphic Chipset that was used for improveing the graphics of the later generation Amiga computers.
              • In general, a video display processor[VDP] (is different from VDC) has some power to processing the contents of the video RAM (filling in an area of RAM), while a video display controller only controls the timing of the video synchronization signals and the access to the video RAM. In another way, the graphics processing unit (GPU) is an advanced form of  VDP and normally does 3D functionality and is the kind of chip that is used in modern personal computers.

        (iii) Transputer

            • It was first designed in 1980 by Inmos and is targeted to the utilization of VLSI technology.
            • A transputer is a specially designed microprocessor with its own local memory and having links to connect one transputer to another transputer for inter-processor communications.
            • A transputer can be used as a single processor system or can be connected to external links, which reduces the construction cost and increases the performance.
            • For example − 16-bit T212, 32-bit T425, the floating point (T800, T805 & T9000) processors.

        (iv) Digital Signal Processor(DSP)

            • This processor is specially designed to process the analog signals into a digital form. This is done by sampling the voltage level at regular time intervals and converting the voltage at that instant into a digital form. This process is performed by a circuit called an analogue to digital converter, A to D converter or ADC.
            • A DSP contains the following components −
              • Program Memory − It stores the programs that DSP will use to process data.
              • Data Memory − It stores the data/information to be processed.
              • Compute Engine − It performs the mathematical processing, accessing the program from the program memory and the data from the data memory.
              • Input/Output − It connects to the outside world.
            • The use of DSP are in −
              • Sound and music synthesis
              • Audio and video compression
              • Video signal processing
              • 2D and 3d graphics acceleration.


        • Besides Micro Computers, Microprocessors are also used in thousands of items i.e., in household appliances, vehicles (and their accessories), tools and test instruments, toys, light switches/dimmers and electrical circuit breakers, smoke alarms, battery packs, and hi-fi audio/visual components.



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