Microprocessor

•The microprocessor is
sometimes referred to as the
'brain' of the personal
computer
•responsible for the processing
of the instructions which make
up computer software.

The key element of all computers, providing
the mathematical and decision making
ability
They operate at ultra-fast speeds – doing
over a billion operations every second
Made up from a semiconductor, Silicon
Current state-of-the-art uPs (Pentium,
Athlon, SPARC, PowerPC) contain complex
circuits consisting of tens of millions of
transistors

•1969
•Clock speed : 108 KHz
• Number of transistors: 2300
• 4-bit register and 4-bit data bus.

•1972
• Clock speed : 800 KHz
• Number of transistor: 3500
•8-bit register and 8-bit data bus.

•1974
•Clock speed : 2 MHz
•Number of transistor: 4500
•8-bit register and data bus.

• 1978
•Clock speed : 4.47 MHz
•Number of transistors: 29000

•1981
•Clock speed : 4,47 MHz
•Number of transistors: 29000
The worlds first PC ran on an Intel
8088 microprocessor

•1982
•Clock speed: 12 MHz
•Number of transistor:134000

•1985
•Number of transistors:275000

•1989
•Number of transistor:1,200,000
•32-bit register and data bus..

•1993

•1995

•1997

•1999

•2000
•Clock speed: 1 GHz

•2005
•Clock speed: 3.6 GHz

•2006/2007
•Clock speed: 3.6 GHz

As there are a great many variations in
architecture between the different kinds
of CPU, we shall begin by looking at a
simplified model of the structure The
simplified model consists of five parts,
which are:•Arithmetic & Logic Unit (ALU)
•Control Unit (CU)
•System Bus
•Register Array
•Memory

•The part of the central
processing unit that deals
with operations such as
addition, subtraction, and
multiplication of integers
and Boolean operations.
•It receives control
signals from the control
unit telling it to carry out
these operations.

•These two tasks are performed by
constructs of logic gates, such as
half adders and full adders.
•While they may be termed
'adders', with the aid of they can
also perform subtraction via use of
inverters and 'two's complement'
arithmetic.

•In most modern processors, the
multiplication and division of integer
values is handled by specific floating-
point hardware within the CPU.
•Earlier processors used either
additional chips known as maths co-
processors, or used a completely
different method to perform the
task.

•logic gates are used within the ALU to
perform a number of different logical
tests, including seeing if an operation
produces a result of zero.

•Comparison operations compare values
in order to determine such things as
whether one number is greater than,
less than or equal to another.
•These operations can be performed by
subtraction of one of the numbers
from the other.
•It can be handled by the logic gates.

•Shifting operations move bits left
or right within a word, with
different operations filling the
gaps created in different ways.
•This is accomplished via the use
of a shift register

•It is responsible for
controlling much of the
operation of the rest of
the processor.
•It does this by issuing
control signals to the
other areas of the
processor, instructing
them on what should be
performed next.

•This is used to decode the
instructions that make up a program
when they are being processed,
•To determine what actions must be
taken in order to process them.
•These decisions are normally taken
by looking at the of the
instruction, together with the
addressing mode used.

•The timer or clock ensures that all
processes and instructions are
carried out and completed at the
right time.
•Pulses are sent to the other areas
of the CPU at regular intervals and
actions only occur when a pulse is
detected.
•This ensures that the operations of
the CPU are synchronised.

•The control logic circuits are used to
create the control signals themselves,
which are then sent around the
processor.
•These signals inform the arithmetic
and logic unit and the register array
what they actions and steps they should
be performing, what data they should
be using to perform said actions, and
what should be done with the results.

•A register is a memory location
within the CPU itself.
•It is designed to be quickly
accessed for purposes of fast
data retrieval.
•Processors normally contain a
register array, which houses many
such registers.
•These contain instructions, data
and other values that may need to
be quickly accessed during the
execution of a program.
•Many different types of
registers are common between
most microprocessor designs.
These are:

•This register is used to hold the
memory address of the next
instruction that has to executed in a
program.
•This is to ensure the CPU knows:1.
at all times where it has reached 2.
Is able to resume following an
execution at the correct point 3.And
the program is executed correctly.

•This is used to hold the current
instruction in the processor while it
is being decoded and executed, in
order for the speed of the whole
execution process to be reduced.
• This is because the time needed to
access the instruction register is
much less than continual checking of
the memory location itself.

•The accumulator is used to hold the
result of operations performed by the
arithmetic and logic unit

•Used for storage of memory
addresses, usually the addresses
involved in the instructions held in the
instruction register.
• The control unit then checks this
register when needing to know which
memory address to check or obtain
data from.

•When an instruction or data is
obtained from the memory or
elsewhere, it is first placed in the
memory buffer register.
•The next action to take is then
determined and carried out, and the
data is moved on to the desired
location.

•The flag register is specially
designed to contain all the
appropriate 1-bit status flags,
which are changed as a result of
operations involving the arithmetic
and logic unit.

•These registers have no specific
purpose, but are generally used for
the quick storage of pieces of data
that are required later in the
program execution.

•The system bus is a cable
which carries data
communication between
the major components of
the computer, including
the microprocessor.
•The system bus consists
of three different groups
of wiring, called: 1. the
data bus, 2. control bus 3.
address bus.
•These all have seperate
responsibilities and
characteristics:

The control bus carries the signals
relating to the control and co-ordination
of the various activities across the
computer, which can be sent from the
control unit within the CPU.
Different architectures result in
differing number of lines of wire within
the control bus, as each line is used to
perform a specific task.
For instance, different, specific lines
are used for each of read, write and
reset requests.

This is used for the exchange of data
between the processor, memory and
peripherals, and is bi-directional so that it
allows data flow in both directions along the
wires.
Again, the number of wires used in the data
bus (sometimes known as the 'width') can
differ.
Each wire is used for the transfer of signals
corresponding to a single bit of binary data.
As such, a greater width allows greater
amounts of data to be transferred at the

The address bus contains the connections between
the microprocessor and memory that carry the
signals relating to the addresses which the CPU is
processing at that time, such as the locations that
the CPU is reading from or writing to.
The width of the address bus corresponds to the
maximum addressing capacity of the bus, or the
largest address within memory that the bus can
work with.
The addresses are transferred in binary format,
with each line of the address bus carrying a single
binary digit. Therefore the maximum address
capacity is equal to two to the power of the
number of lines present (2^lines).

Microprocessor

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