This document provides an introduction to microprocessors, including definitions of basic terms, classifications of microprocessors, memory units, input and output devices, and how technology has improved microprocessors over generations. It discusses the origin of microprocessors and how they have evolved from 4-bit processors in the first generation to 64-bit processors today. The document also summarizes different types of microprocessors like general purpose, microcontrollers, and special purpose processors.

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Evolution & Introduction
to Microprocessor
Introduction
Basic terms
Types of Microprocessor
Microprocessor based system
Origin of microprocessor
Classification of Microprocessor
Memory unit
Input & Output devices
Functions of I/O ports
Technology improvements adapted to microprocessor & Computer
Contents:

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Introduction
Microprocessor is an electronic chip that functions as the central
processing unit (CPU) of a computer
In other words, we can call microprocessor as the heart of any
computer system.
Some may call the microprocessors as the brain of the computers.
The microprocessor based systems with limited resources are
called as microcomputers.
Now-a-days microprocessors are found in almost all electronic
machines and appliances in its different form.
Some common devices using microprocessors are computer
printers, automobiles, washing machines, microwave ovens,
mobile phones, fax machines, Xerox machines and advanced
instruments like radar, satellites, flights etc.,
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Any middle class house-hold will have about a dozens
microprocessor in different forms inside various appliances.
The recent developments in electronic industry and the large
scale integration of devices has led to rapid cost reduction and
more and more application of microprocessors and its derivatives.
Almost all microprocessors use the basic concept of “stored
program execution”.
By this concept, programs or the instructions to be executed by
the microprocessor are stored sequentially in memory locations.
The microprocessor or the processor in general will fetch the
instructions one after the other and execute them it in its
arithmetic and logic unit.

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A microprocessor can be programmed to do any task that can be
written and programmed by the user.
So, in order to work with the microprocessor, it is necessary for
the user to know about the internal resources and features of the
microprocessor.
The programmers must also understand the instructions that a
microprocessor can support.
Every microprocessor will have its own associated set of
instructions that it supports and this list is given by all the
microprocessor manufacturers
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The instruction set for microprocessors is given in two forms
a) One in mnemonic which is comparatively easy to understand
b) The other in binary machine code which the microprocessor really
works upon and difficult to understand by us.
Programs are written using mnemonics called the assembly level
language and then they are converted into binary machine level
language.
This conversion can be done manually or using an application called
assembler.
In general, the programs are written by the user for a microprocessor to
work with real world data.
These data are available in many forms and are from many sources.
To give this data to the microprocessor, the microprocessor based
systems need some input interfacing circuits and some electronic
processing circuits.
These circuits include data converters and ports
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After processing the real world data, the output from the
microprocessor must be taken out to give to final end effect
instrument or circuits.
This again needs interfacing circuits and ports.
So, a microprocessor based system will need a set of memory
units, set of interfacing circuits for inputs and a set of interfacing
circuits for outputs.
All circuits put together along with microprocessor are called as
microcomputer system.
The physical components of the microcomputer system are in
general called as hardware.
The program which makes this hardware useful is called as
software.
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Basic terms
Chip
a) A chip or an integrated circuit is a small, thin piece
of silicon with the required circuit and transistors
etched on it to perform a particular function.
b) Simpler processors might consist of a few thousand
transistors etched onto a silicon base just a few
millimeters square.

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Bit
a) A bit means a single binary digit.
b) Also, the bit is the fundamental storage unit of
computer memory. In binary, bit can have only two
values, 0 or 1, whereas a decimal digit can have 10
values, represented by symbols 0 through 9.
Bit Size
The bit size of a microprocessor refers to the number
of bits that can be processed simultaneously by the
basic arithmetic circuits of the microprocessor.
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Word
A number of bits grouped together for processing is
called as word. In microprocessors, the word in
general refers to the basic data size or bit size that can
processed by the ALU of the processor. 16-bit binary
number is called a word in a 16-bit processor.
Memory word
The number of bits that can be stored in a register of
memory element is called a memory word. Mostly all
memory units use 8-bits as their memory word.
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Byte
An 8-bit word is referred to as a byte.
Nibble
A 4-bit word is referred to as a nibble.
Kilobyte
A collection of 1024 bytes is called a kilobyte.
Megabyte
A collection of 1024 Kbytes is called a megabyte.
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RAM or R/W memory
Random Access Memory or Read/ Write memory is
the type of semiconductor memory in which a
particular memory location can be erased and
written with a new data at any time.
These memory units are volatile, which means that
the content of the memory is erased when the power
to the chip is disrupted.
The access of the individual memory location can be
done randomly. In microprocessors, the RAM is used
to store data.
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DRAM
a) Dynamic Random Access Memory is a semiconductor
memory in which the stored contents need to be
refreshed repeatedly at about thousands of times per
second.
b) Without refreshing, the stored data will be lost.
c) These memory chips are preferred in a computer system
because it is economical although slower.
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SRAM
Static Random Access Memory chips keep the data
stored in it as long as power is available. There is no
need for refreshing. In terms of speed, SRAM is faster.
ROM
Read Only Memory are memory devices whose
contents are retained even after removing the power
supply.
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Arithmetic and Logic Unit (ALU)
a) ALU is a digital circuit present in the microprocessor
to do performs arithmetic and logic operations on
digital data.
b) The typical operations performed by the ALU are
addition, subtraction, Logical AND, logical OR and
comparison of binary data.
c) Generally, the functions of the ALU of a
microprocessor will decide the functionality that can
be performed by the processor.
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Microcontroller
Microcontroller is a chip that includes
microprocessor, memory and I/O signal ports.
Microcontrollers can be called as single chip
microcomputers.
Microcomputer
The system formed by interfacing microprocessor
with memory, and I/O devices to work with the
required program is called microcomputer.
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Bus
The bus in a microprocessor system refers to a group of
wires or signals having a common functionality
System Bus
The System bus is a group of signals used for
communication between the microprocessor and
peripherals.
Firmware
Software written for a microprocessor application
without provision for changes. These are stored into
permanent storage or ROM of the computer system.
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Input device
The devices that are used for giving data to the
microcomputer system are called as input devices.
Usually keyboard and mouse are the input devices
through which data and instructions are given to
computer.
Output device
The devices that are used for getting data out from the
microprocessor or microcomputer system are called
as output devices. A display screen, printer and
displays are the common output devices.
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Clock
The circuit in the computer that generates the
sequence of evenly spaced pulses to synchronize the
activities of the processor and its peripherals.
The clock speed determines the speed of the operation
of the computer.
The computer with a high frequency clock works
faster. Normally the clock frequency is in the range of
Mega Hertz, MHz or Giga Hertz, GHz.
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Types of Processors
Two types of processors are manufactured
a) The microprocessor
b) The microcontroller
The general purpose microprocessors give the computers
all the necessary computing power.
These microprocessors need additional circuitry elements
such as memory devices, I/O ports to connect the input
and output devices.
All microprocessor based systems need two types of
memories – RAM and ROM.

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Microcontrollers
The microcontrollers are the microprocessors designed especially for control
applications.
Microcontrollers contain memory units and I/O ports inside a chip in addition
to the CPU part.
Microcontrollers are otherwise called as embedded controllers are generally
used to control and operate smart machines.
Some of the machines using microcontrollers are microwave ovens, washing
machines, sewing machines, automobile ignition systems, computer printers
and fax machines etc.
Out of 100 processor chips manufactured, 99 are embedded processors and
remaining 1 processor alone goes into general computers.
Lots of semiconductor companies are in the market of microcontrollers and any
application development engineer is flooded with the variety of
microcontrollers as the choice.
The system consists of CPU, memory and I/O ports
The interfacing of the processor with the other parts of the
microcomputer system needs three bus architecture.
The three buses are
a) Data bus,
b) Address bus
c) Control bus
Microprocessor based system

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Each memory location or I/O port is identified by a specific
address similar to the postal address.
Here, in microprocessor systems, the addresses are all in binary
and in general written in hexadecimal number format.
The address is a unique pattern used to identify a location in
memory or I/O port.
The address bus consists of many lines that can have the digital
data sent by the processor.
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An address bus of 8 bits 28 different memory locations.
Similarly, the 16-bit address bus can address 216 different
addresses. Its address ranges from 0000H to FFFFH.
The higher the number of lines of address bus is, the more the
locations the processor is able to manage.
A control bus is needed for proper data transfer between the
processor and other peripherals.
The control bus basically consists of signals like selecting the
proper memory or I/O device from the address; signal to indicate
the direction of data transfer; and the signal to synchronize data
transfer between slow devices.
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Origin of Microprocessor
The breakthrough in transistor technology led to the
introduction of minicomputers of the 1960s and the
personal computer revolution of the 1970s.
Intel was the first MPU producer and has been holding a
large share in the world market of this product.
Microprocessors evolution is categorized into five
generations
first, second, third, fourth, and fifth generations.
First Generation (1971-73)
The microprocessors that were introduced in 1971 to
1972 were referred to as the first generation systems.
Intel Corporation introduced 4-bit 4004 at 108 kHz, the
first microprocessor in 1971, co-developed by Busicom, a
Japanese manufacturer of calculators.
In 1972, Intel made the 8-bit 8008 and 8080
microprocessors.

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Second Generation (1974-78)
Very large-scale integration (VLSI) lead to chips which
had speeds up to hundreds of millions of switching per
second.
The second generation marked the beginning of very
efficient 8 – bit microprocessors.
Some of the popular processors were Motorola’s 6800
and 6809 and Intel’s 8085, Zilog’s Z80.
The distinction between the first and second generation
devices was primarily the use of newer semiconductor
technology to fabricate the chips.
They were manufactured using NMOS technology.
Third Generation (1979-80)
Introduced in 1978, dominated by Intel’s 8086 and the Zilog
Z8000, which were 16-bit processors with minicomputer-like
performance, have 16-bit arithmetic and pipelined instruction
processing.
Transistor counts about 250,000.
Motorola’s MC68020, incorporated an on-chip cache for the first
time and the depth of the pipeline increased to five or more
stages.
HMOS - speed-power-product of HMOS is four times better than
that of NMOS.
HMOS can accommodate twice the circuit density compared to
NMOS.

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Fourth Generation (1981-95)
Designs with more than a million transistors in a package.
32 bits microprocessors introduced – Intel 80386 and
Motorola 68020/68030.
Fabricated using low-power version of the HMOS
technology called HCMOS.
Fifth Generation (1995 till date)
Employed decoupled super scalar processing.
Chips carry on-chip functionalities and improvements in
the speed of memory and I/O devices
Design surpassed 10 million transistors per chip.
Introduction of 64-bit processors
Intel leads the show with Pentium, Celeron and dual and
quad core processors working with up to 3.5GHz speed.

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General Purpose Processors - Comparison
Microprocessors can be classified based on their purpose,
architecture, specifications and applications.
Based on the size of the data that the microprocessor can
handle, they are classified as 4-bit, 8-bit, 16-bit, 32-bit and
64-bit microprocessors.
Based on the application of the processors, they are
classified as i) General purpose processors,
ii) Microcontrollers and
iii) Special purpose processors.
Classification of Microprocessors

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General Purpose Processors
General purpose processors are those which are used in
general computer system integration and can be used by the
programmer for any application.
Common microprocessor such as Intel 8085 to Intel Pentium
processors are examples of general purpose processors.
Microcontrollers are the microprocessor chips with in built
hardware for the memory and ports.
These chips are can be programmed by the user for any generic
control applications.
Special Purpose Processors
Special purpose processors are designed specifically to
handle special functions required for an application.
The digital signal processors are examples for the special
purpose processors and these have special instructions to
handle signal processing.
The Application Specific Integrated Circuits (ASIC) chips
are also the examples of this category of microprocessors.

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Classification of microprocessorsClassification of microprocessorsClassification of microprocessorsClassification of microprocessors
Based on the architecture and hardware of the processors, they
are classified as
a)RISC processors,
b)CISC processors,
c)VLIW processors and
d)Superscalar processors.
Reduced Instruction Set Architecture’, is a processor architecture
that supports limited or small number of machine language
instructions.
RISC processors can execute the programs faster than CISC processors.
CISC – Complex Instruction Set Computing architecture
a) CISC processors have about 70 to few hundred instructions and are
easier to program.
b) CISC processors are slower and more expensive than RISC
processors.
c) Very Long Instruction Word (VLIW) processors have instruction
composed of many machine operations which can be executed in
parallel.
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This is achieved by many functional units operating in
parallel.
It has large number of registers and instruction level
parallelism is achieved.
Superscalar processors are using complex hardware to
achieve parallelism.
It is possible to have overlapping of execution of
instructions in order to increase the speed of execution.
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Memory UnitMemory UnitMemory UnitMemory Unit –––– An IntroductionAn IntroductionAn IntroductionAn Introduction
Memory unit is the integral part of any microcomputer system
and its primary purpose is to hold program and data.
The major design goal of memory unit is to allow it to operate
at a speed close to that of the processor.
The cost factor inhibits the design of entire memory unit with
single technology that guarantees high speed.
In order to seek a trade-off between the cost and operating
speed, a memory system is usually designed with different
technologies such as solid state, magnetic and optical.

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A microcomputer memory can be logically
divided into four groups
a) Processor memory/ register
b) Cache memory
c) Primary or Main Memory
d) Secondary memory
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Processor Memory refers to a set of CPU registers. Processor
registers are the first set of storage device available for the
programmers to store any data.
But they are generally few in number up to about few tens to
hundreds.
As these registers are available within the processor, they are
the fastest memory registers.
The main disadvantage is the cost involved which forces to
restrict the number to very few registers of few bytes.
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Cache memory is the fastest external memory to the processor
and they are placed close to the processor.
The instructions to be executed are placed in cache memory for
access by the processor. These are in few kilobytes in size.
These are semiconductor RAMs and are volatile.
The processor will fetch the next instruction from the cache
memory and if the instruction is not in cache, it will refer to
primary memory.
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Primary memory is the storage area from which all the programs
are executed.
All the programs and corresponding data must be within primary
memory prior to execution.
The size of primary memory is much larger compared to
processor memory and cache memory but its operating speed is
slower than them.
The primary memory in a system varies from few Kilobytes to
about 1 Megabyte.
Secondary memory refers to the storage medium for huge files
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These are not accessed directly and very frequently by
the microprocessor in a computer system.
They comprises of slow devices such as magnetic tapes
and optical disks.
Sometimes they are referred to as auxiliary or backup
store.
Stored information in a magnetic tape or magnetic disk
is not lost when the power is turned off.
Therefore these storage devices are called nonvolatile
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Primary MemoryPrimary MemoryPrimary MemoryPrimary Memory ---- ClassificationClassificationClassificationClassification
Primary memory normally includes ROM (Read Only
Memory) and RAM (Random Access Memory).
Microprocessor based systems have at least one RAM and
ROM chips in it.
Information stored in semiconductor random access
memories RAM will be lost if the power is turned off.
This property is known as volatility and hence, RAMs are
usually called volatile memories.
ROM is a nonvolatile memory.

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As the name implies, a ROM permits only a read access.
There are many kinds of this category.
Mask Programmable ROMS are custom made for the
customer and their contents are programmed by the
manufacturer.
Since they are mass produced, they are inexpensive. The
customer can not erase or program it afterwards.
Programmable ROMs are the devices which can be
programmed by the user at the user’s place or field.
The main disadvantage of PROMs is that they cannot be
erased and reprogrammed
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EPROMEPROMEPROMEPROM
Erasable and Programmable ROMs (EPROMs) allow the
erasure and reprogramming of the content by the user.
In an EPROM, programs are entered using electrical impulses
and the stored information is erased using UV rays.
Electrically Erasable PROMs (EEPROMs) or Electrically
Alterable ROMs (EAROMs) allow the users to erase its contents
by electrical means and also reprogramming by electrical
signals.
EEPROMs are different from RAMs in the electrical signal
required to erase and program. EEPROMs require a higher
voltage for erasing and programming other than the normal 5V
supply.
Static RAM
In a semiconductor memory constructed using bipolar
transistors, the information is stored in the form of
voltage levels in flip-flops.
Such memories are called static RAMs because stored
information remains constant for some period of time.
Static RAM maintains information in active circuits,
power is required even when the chip is inactive or
standby mode.
Hence, static RAMs require large power supplies.
Also each static RAM cell is about four times larger in
area than an equivalent dynamic cell.

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Dynamic RAM
Semiconductor memories designed using MOS
transistors, the information is held in the form of
electrical charges in capacitors.
The stored charge has the tendency of get leaked away.
These memories are referred to as dynamic RAMs.
In order to prevent any information loss, dynamic
RAMS have to be refreshed at regular intervals.
Refreshing means boosting the signal level and writing
it back.
This activity is performed using a hardware unit called
“refresh logic”.
Differences

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Input and Output Devices
The input/output or I/O section allows the computer to take
in data from the outside world or send data to the outside
world.
Peripherals such as keyboards, video display terminals,
printers, and modems are connected to the I/O section.
These allow the user and the computer to communicate with
each other.
The actual physical devices used to interface the computer
buses to external systems are often called ports.
Function of I/O Ports
An input port allows data from a keyboard, an A/D converter, or
some other source to be read into the computer under control of
the CPU.
An output port is used to send data from the computer to
peripheral devices, such as a video display terminal, a printer, or a
D/A converter.
Simplest type of input or output port is just a set of parallel D flip-
flops.
If they are being used as an input port, the D inputs are connected
to the external device, and the Q outputs are connected to the data
bus which can take the data to the CPU.

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Data will then be transferred to the data bus when they are
enabled by a control signal from the CPU.
In a system, where they are being used as an output port,
the D inputs of the latches are connected to the data bus,
and the Q outputs are connected to some external device.
Data sent out on the data bus by the CPU will be
transferred to the external device when the latches are
enabled by a control signal from the CPU.
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Input Devices
Input devices include typewriter-like keyboards; hand-held devices
such as the mouse, trackball, joystick, and special pen with pressure-
sensitive pad; and microphones.
The simplest input device is a switch.
Input devices can also be sensors that provide information about
their environment temperature, pressure, and so forth to a computer.
Another direct-entry mechanism is the optical laser scanner (e.g.,
scanners used with point-of-sale terminals in retail stores) that can
read bar-coded data or optical character fonts.

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Output Devices
An output is any device through which the user can receive
the results from the computer.
The output can be any display which can be changing fast
or hard copies print out. Some other forms of output are
sounds and alarms.
The simplest output devices used in almost all
microprocessor based systems or computer systems are
the LEDs or the seven segment LED displays and LCD.
displays.
The advanced video display terminals (either cathode-ray tubes or
liquid crystal displays), ink-jet and laser printers, are the common
output devices nowadays.
Some output devices can be used to directly control machineries.
Some devices, such as display terminals with touch screen, may
provide both input and output.
Modems and other network interface cards can also be called as
output devices as they enable the transmission and reception of data
between computers.
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Technological Improvements
Technology improvements are taking place fast in the
microprocessor, microcomputer and personal computer
systems.
The technical and research improvements in the field of
microprocessor technology is listed below.
Increase in data bus / address bus width. The
processing capability of the microprocessor can be
drastically improved by increasing data size.
Increase in speed
As the data to be processed by the microprocessors
and computers increased in volume, it became a
necessity to increase the speed of the processor.
By high speed processors, the user can get the
results faster even with the large data volumes.
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Reduction in size and increase in capability
The trend in microprocessor technology is to include large amount of
peripherals such as memory and I/O ports within a single chip.
Microcontrollers are manufactured by all semiconductor
manufacturers in this aspect.
Development in the processing of large scale integration has lead to
small chips of microprocessors with large built in peripherals.
We have now processors with large amount of flash memory available
in the market.
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Development of external peripherals
The use of computers in all the fields have resulted in the
development of many fast and advanced peripheral devices
to be interfaced with the microprocessor.
For example, applications of microprocessors in medical field
has resulted in many handheld electronic devices with the
specialized input sensors and output printers etc.
The faster peripherals can increase the speed of processor
execution and a good user interface.

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Increase in memory size and speed
The developments in the Integrated circuit technology
have lead to developments in the reduction of the
memory size and the increase in memory speed.
This reduces the memory access time of the processor
and so will result in the higher speed of execution.
Also more amount of memory per unit area is possible
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The microprocessors are largely used in handheld devices
operated from the battery source.
This has resulted in the research towards reduction of
power consumption in the microprocessor chips.
As power consumption is reduced, the devices can work
for more time with one full charge of batteries.
There are many devices operating at 3.3V are even lower
and have low power consumption.
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Summary
Microprocessor is an electronic circuit that functions as the
central processing unit (CPU) of a computer, providing
computational control.
The microprocessor is the controlling element in a computer
system.
The microprocessor performs data transfers, does simple
arithmetic and logic operations, and makes simple decisions.
The basic operation of the microprocessor is to fetch instructions
stored in the memory and execute them one y one in sequence.
Microprocessors are used in almost all advanced electronic systems.
Microcontrollers are advanced forms of microprocessors with
memory and ports present within the chip.
A microcomputer system is made y interfacing memory and I/O
devices to a microprocessor
Microprocessor evolution is classified into five generations
The processors that are currently in use belong to the fifth
generation.
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