Marathwada Institute of Technology, Bulandshahr (U.P.

DEPARTMENT OF COMPUTER SCIENCE AND ENGINEERING

SUBJECT NOTES

KCA 101 : Computer Organization And Architechture……

(UNIT –I) Introduction:- Functional units of digital system and their interconnections, buses, bus
architecture, types of buses and bus arbitration. Register, bus and memory transfer. Processor
organization: general registers organization, stack organization and addressing modes

(UNIT-2) :- Arithmetic and logic unit: Look ahead carries adders. Multiplication: Signed operand
multiplication, Booths algorithm and array multiplier. Division and logic operations, Floating point
arithmetic operation, Arithmetic & logic unit design, IEEE Standard for Floating Point Numbers.

(UNIT-3):- Control Unit: Instruction types, formats, instruction cycles and sub cycles (fetch and
execute etc), micro operations, execution of a complete instruction. Program Control, Reduced
Instruction Set Computer, Pipelining. Hardwire and micro programmed control: micro-program
sequencing, concept of horizontal and vertical microprogramming.

(UNIT-4):- Memory: Basic concept and hierarchy, semiconductor RAM memories, 2D & 2 1/2D
memory organization. ROM memories, Cache memories: concept and design issues & performance,
address mapping and replacement Auxiliary memories: magnetic disk, magnetic tape and optical
disks Virtual memory: concept implementation.

(UNIT-5):- Input / Output: Peripheral devices, I/O interface, I/O ports, Interrupts: interrupt
hardware, types of interrupts and exceptions. Modes of Data Transfer: Programmed I/O, interrupt
initiated I/O and Direct Memory Access., I/O channels and processors. Serial Communication:
Synchronous & asynchronous communication, standard communication interfaces.

B.tech 3rd sem /KCS 302/COA/U-1/N-1/Ms. Rashmi Bhardwaj

THE INTRODUCTION OF COMPUTER ARCHITECHTURE :-

In computer engineering, computer architecture is a set of rules and methods that
describe the functionality, organization, and implementation of computer systems. ... In
other definitions computer architecture involves instruction set architecture design,
microarchitecture design, logic design, and implementation.

Computer architecture is a specification detailing how a set of software and hardware

technology standards interact to form a computer system or platform.

DIGITAL SYSTEMS:-
A digital system is a system that stores data in a discrete way. The opposite is an
analogue (US- analog) system, which stores the data in a continuous way. Usually, digital
systems store the information in a binary way; that is, every bit of information can not have
a value other than zero (off) or one (on).

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 FUNCTIONAL UNITS OF DIGITAL SYSTEM AND THEIR
INTERCONNECTION:-
o A computer organization describes the functions and design of the various units
of a digital system.
o A general-purpose computer system is the best-known example of a digital
system. Other examples include telephone switching exchanges, digital
voltmeters, digital counters, electronic calculators and digital displays.
o Computer architecture deals with the specification of the instruction set and the
hardware units that implement the instructions.
o Computer hardware consists of electronic circuits, displays, magnetic and optic
storage media and also the communication facilities.
o Functional units are a part of a CPU that performs the operations and calculations
called for by the computer program.
o Functional units of a computer system are parts of the CPU (Central Processing
Unit) that performs the operations and calculations called for by the computer
program. A computer consists of five main components namely, Input unit,
Central Processing Unit, Memory unit Arithmetic & logical unit, Control unit and
an Output unit.

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Input unit
o Input units are used by the computer to read the data. The most commonly used
input devices are keyboards, mouse, joysticks, trackballs, microphones, etc.
o However, the most well-known input device is a keyboard. Whenever a key is
pressed, the corresponding letter or digit is automatically translated into its
corresponding binary code and transmitted over a cable to either the memory or
the processor.

Central processing unit

o Central processing unit commonly known as CPU can be referred as an electronic
circuitry within a computer that carries out the instructions given by a computer
program by performing the basic arithmetic, logical, control and input/output
(I/O) operations specified by the instructions.

Memory unit
o The Memory unit can be referred to as the storage area in which programs are
kept which are running, and that contains data needed by the running programs.
o The Memory unit can be categorized in two ways namely, primary memory and
secondary memory.
o It enables a processor to access running execution applications and services that
are temporarily stored in a specific memory location.
o Primary storage is the fastest memory that operates at electronic speeds. Primary
memory contains a large number of semiconductor storage cells, capable of
storing a bit of information. The word length of a computer is between 16-64 bits.
o It is also known as the volatile form of memory, means when the computer is
shut down, anything contained in RAM is lost.
o Cache memory is also a kind of memory which is used to fetch the data very
soon. They are highly coupled with the processor.
o The most common examples of primary memory are RAM and ROM.
o Secondary memory is used when a large amount of data and programs have to
be stored for a long-term basis.
o It is also known as the Non-volatile memory form of memory, means the data is
stored permanently irrespective of shut down.
o The most common examples of secondary memory are magnetic disks, magnetic
tapes, and optical disks.

Arithmetic & logical unit

o Most of all the arithmetic and logical operations of a computer are executed in the
ALU (Arithmetic and Logical Unit) of the processor. It performs arithmetic
operations like addition, subtraction, multiplication, division and also the logical
operations like AND, OR, NOT operations.

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 Control unit
o The control unit is a component of a computer's central processing unit that
coordinates the operation of the processor. It tells the computer's memory,
arithmetic/logic unit and input and output devices how to respond to a program's
instructions.
o The control unit is also known as the nerve center of a computer system.
o Let's us consider an example of addition of two operands by the instruction given
as Add LOCA, RO. This instruction adds the memory location LOCA to the operand
in the register RO and places the sum in the register RO. This instruction
internally performs several steps.

Output Unit
o The primary function of the output unit is to send the processed results to the
user. Output devices display information in a way that the user can understand.
o Output devices are pieces of equipment that are used to generate information or
any other response processed by the computer. These devices display information
that has been held or generated within a computer.
o The most common example of an output device is a monitor.

BUSES AND BUSES ARCHITECHTURE :-

Bus is a subsystem that is used to transfer data and other information between devices. Means various
devices in computer like(Memory, CPU, I/O and Other) are communicate with each other
through buses.In general, a bus is said to be as the communication pathway connecting two or more
devices.

A key characteristics of a bus is that it is a shared transmission medium,as multiple devices are
attached to a bus.

Typically, a bus consists of multiple communication Pathways or lines which are either in the form of
wires or metal lines etched in a card or board(Printed Circuit Board).Each line is capable of
transmitting binary 1 and binary 0.

Computer System Contains a number of different buses that provide pathways between components
at various levels of computer system hierarchy.
But before discussing them i.e., types of buses , i will first describe here one of the most important
aspect of buses which is described below-

Any Bus consists,typically of form about 50 to 100 of separate lines.And on any bus, the lines may
generally be classified into three functional groups, as depicted in figure below:

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 Data Lines:
Data Lines provide a path for moving data between system modules.It is bidirectional which
means data lines are used to transfer data in both directions.As an example, CPU can read data
on these lines drom memory as well as send data out of these lines to a memory location or to a
port.And in any bus the no. of lines in data lines are either 8,16,32 or more depending on size
of bus.These lines , collectively are called as data bus.

 Address Lines:
Address Lines are collectively called as address bus.In any bus, the no. of lines in address are
usually 16,20,24, or more depending on type and architecture of bus.On these lines, CPU
sends out the address of memory location on I/O Port that is to be written on or read from.In
short, it is an internal channel from CPU to Memory across which the address of data(not data)
are transmitted.Here the communication is one way that is, the address is send from CPU to
Memory and I/O Port but not Memory and I/O port send address to CPU on that line and hence
these lines are unidirectional.

 Control Lines:
Control Lines are collectively called as Control Bus.Control Lines are gateway used to transmit
and receives control signals between the microprocessor and various devices attached to it.In
other words, Control Lines are used by CPUs for Communicating with other devices within the
computer.As an example-CPU sends signals on the Control bus to enable the outputs of address
memory devices and port devices.Typical Control Lines signals are:

-Memory Read
-Memory Write
-I/O Read

-I/O Write
-Bus Request
-Bus Grant, etc.

Operation of Bus
The Operation of Bus is as follows:

 If One module wishes to send data to another, it must do two things:

1.Obtain the use of module Bus

2.Transfer for data to the Bus

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 If one module wishes to request data from another module, it must:
1.Obtain the use of Bus
2.Transfer a request to other module over the appropriate control and address lines.It must then
wait for that second module to send the data.

Types Of Bus
There are variety of Buses, but here i will describe only those that are widely used.

 System Bus:
A Bus that connects major computer components (Processor, Memory, I/O) is called a
System Bus.It is a single computer bus among all Buses that connects all these
components of a computer system.And it is the only Bus, in which data lines, address,
control lines all are present.It is also Known as "front side " Bus.It is faster than peripheral
Bus(PCI, ISA, etc) but slower than backside Bus.

 Peripheral Bus(I/O Bus /External Bus):

Peripheral Bus also known as "I/O Bus".It is data pathway that connects peripheral devices to
the CPU.In other words , in computing, a peripheral bus is a computer bus designed to support
computer peripheral like printers,hard drives.The PCI and USB buses are commonly used
Peripheral Buses, and are today used in commonly many PCs.Now we will discuss both of
them in brief:

PCI(Peripheral Component Interconnect): PCI Bus connects the CPU and expansion
boards such as modem cards ,network cards and sound cards.These expansion boards are
normally plugged into expansion slots on the motherboard.That's why PCI bus is also
known as expansion bus or external Bus.

USB(Universal Serial Bus): Universal Serial Bus is used to attach USB devices like Pen
Drive, etc to CPU.

 Local Bus:
Local Bus are the traditional I/O(Peripheral) buses such as ISA,MCA, or EISA Buses.Now we
will discuss about each in brief one by one.

ISA(Industry Standard Architecture Bus): The ISA Bus permit bus mastering i.e., it
enabled peripheral connected directly to the bus to communicate directly with other
peripherals without going through the processor.One of the consequences of bus mastering
is Direct Memory Access.Up to end of 1990s almost all PCs computers were equipped with
ISA Bus, but it was progressively replaced by the PCI Bus,which offer a better performance.

MCA(Micro Channel Architecture): It is an improved proprietary bus designed by IBM

in 1987 to be used in their PS/2 lines of computers.

EISA(Extended Industry Standard Architecture): The EISA Bus use connectors that
were same size as the ISA connectors but with 4 rows of contacts instead of 2 for 32 bit
addressing.

 High Speed Bus:

High Speed Bus are specifically designed to support high capacity I/O devices.High Speed Bus
brings high demand devices into closer integration with the processor.This Bus supports
connection to high speed LANs, such as Fast Ethernet at 100 Mbps, video and graphic
workstation, firewire etc.

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