Computer Architecture

1
Computer Architecture Operating System O.S.

• Architecture Functions as performed by a
  Computer System.
• Organization Hardware blocks of a Computer
  System that helps to implement the Architecture.
• - CPU.
• - Memory ( Main Secondary).
• - Input Output Peripherals.
• Operating System A System Software that helps
  all type of users to operate a computer System.

2
The Functions of a Computer

• It is a general purpose, user programmable, A
  program Meaningful Group of instructions
  written in a specific language aimed to do a
  specific task. electronic gadget capable of
  doing the following tasks
• Data Processing (Numeric Non Numeric) with
  high degree of accuracy at a pretty high speed.
• Storage of huge amount of information of various
  types Text (in various formats) , Picture,
  Audio, Video with reasonably high access speed
  Information Bank.
• Communication Gateway Link to the World.

3
Computer Vs. Other Electronic Gadgets

• Full User programmability Under some support
  environment. Like do not divide if the divisor is
  0 can be achieved through programming in a
  computer but such a thing cannot be achieved in a
  calculator /organizer.
• Wide Connectivity Options To other computers and
  various types of peripherals.
• Ease of upgradeability By installing new
  packages , connecting state of the art
  peripherals, enhancing memory etc.
• Downward Compatibility Even after several
  phases of up-gradation, almost all computer
  systems do provide support for several old
  versions of Hardware as well as software . This
  enables investments made at any stage of a
  computer system useful and effective for many
  years to come.

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Data Processing Activity of any Typical Computer
(achieved by executing some program)

• Numeric Operations involving manipulation of
  Integers and Floating Point Numbers that includes
  very large values too (achieved through Special
  Application Programs) .
• Logical Operations like comparing two items.
• 3.Non Numeric Operations that includes among all
  things the following
• 3a) Arranging Data Items like
  preparation of merit list.
• 3b) Manipulating Pictures
  Graphics.
• 3c) Multimedia applications (
  Audio, Video, Graphics, Video)
• 3d) Create, format, send receive
  messages of various forms.

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The Building Blocks of any Computer System

• The Central Processing Unit C.P.U. performs
  processing control.
• The Memory System ( Internal as well as
  Peripheral Devices) the storage repository.
• The various Input Output Peripheral Devices.
• The links/connections between these Components
  The various Bus .

6
The Operating System

• The Operating System is a Modular, Expandable
  Program which is
• pre-designed stored in the Memory System
  that , when executed by the CPU, makes all the
  components of a Computer function in unison as
  well as enables real world users to interact with
  the Computer System.

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The Memory System The Common Storage Repository
of any Computer System

• The Memory System of any Computer acts as the
  Common Storage repository for the following
• The Operating System includes various Drivers ,
  Resource Managers, Command Interpreters
  Graphic User Interfaces (GUIs).
• Other System Programs like Translator ( Compiler,
  Assembler) , Linker, Loader, System Libraries.
• Various Application Modules like MS-Office,
  Internet Browsers.
• Data in various forms ( Text, Pictures, Images,
  Audio Video)

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Computer Components- 1 The Central
Processing Unit C.P.U. Structure Outline

• Each every computer MUST carry out some form
  of processing , hence it must possess
• A Processing Element / Processing Unit /
  Processor Arithmetic, Logical, Manipulation of
  Messages The Arithmetic Logic Unit (ALU) .
• Some form of electronic local storage /
  Registers Scratchpad .
• The processing tools i.e. the instructions
  available for processing . These instructions
  constitute any program framed to accomplish any
  kind of processing implemented through the
  Control Unit .
• Proper sequencing the processing steps /
  instructions as well as controlling the various
  components to achieve the desired result through
  the Control Unit.
• Interface to the other components of the Computer
  ( achieved through Registers Control Unit ).
• The above are closely linked together hence are
  all encapsulated into the C.P.U. Central
  Processing Unit.

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The Functions of the CPU

• The Central Processing Unit performs the
  following tasks by executing Instructions of some
  specific Operating System Modules / System
  program stored in the Memory System.
• 1) Controlling all peripheral devices.
  Relevant Device Driver Program(s).
• 2) Communicating with all types of Remote
  Devices.
• Network Protocol Program (s) acting on
  Network Cards
• 3) Recognizing user commands Command
  Interpreters / GUI (Graphic User Interface) .
• 4) Inputting Data Device Driver of the
  O.S..
• 5) Producing Output (on screen /or on
  printer) after obtaining Data from
  Main/Secondary Memory.Device Driver of the O.S.
• 6) Performing arithmetic logical
  operations. As per Specified Instruction(s) of
  the executing program (s)

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The Components of the C.P.U.

• Arithmetic Logical Processing Unit The
  A.L.U.
• Associated Data Storage Components / Scratch Pad
  Storage. Electronic Storage (The Registers).
• The implementation of the Instruction Set as well
  as the unit that controls sequences all
  operations in accordance with the supported
  Instruction Set The Control Unit .
• The interface with other components of a
  Computer Special Purpose Registers along with
  associated controls .
• ( All will be illustrated in due course ).

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The Components of the CPU

Storage Interface Registers
ALU
Control Unit
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The CPU Performance Parameters - 1

• N.B All the activities of any Computer
  System are being carried out by the CPU by
  executing some machine level /low level
  instruction.
• 1. CPU Speed Each machine instruction takes
  a definite time to complete execution. This time
  is measured in terms of the Number of CPU Clock
  Periods needed to execute that instruction ( The
  Instruction Latency).
• Hence one way to measure the CPU speed is
  Number of Instructions executed / second (termed
  as the Throughput) .
• Typical unit is MIPS (Millions of
  Instructions per second) or MFLOPS (Millions of
  Floating point Operations performed per second.)
  
• However one normally finds the CPU
  Clock frequency as rough estimate of its speed
  i.e. higher the clock frequency higher will be
  the CPU speed.
• But in actual terms speed will be
  affected depending on the most frequently used
  instructions hence the Throughput happens to be a
  more fair estimate of the CPU speed estimated by
  executing some benchmark programs .

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The CPU Performance Parameters - 2

• 2. CPU Processing Power The Operand Size (in
  bits) it can handle at one go i.e. in a single
  machine instruction normally. This is directly
  related to its ALU ( Arithmetic Logic Unit a
  purely combinational Circuit) width.
• e.g. Pentium is a 32 Bit CPU ? Any Machine
  level instruction of a Pentium Processor can
  handle 32 bit operands or Pentium contains 32
  bit Integer ALUs.
• N.B This Operand Sized based classification is
  interesting in the sense that any n bit CPU can
  also be used to handle larger sized data provided
  one writes proper programs to achieve that which
  gets translated into n bit processing
  instructions by the Translator Program (The
  Compiler).

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Computer Components 2
The Memory

• Memory Essential to create any form of
  Information Bank/ Common Storage Repository ( as
  illustrated earlier).
• Wide range types of Memory Storage Media
  are available/ in use now a days .

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Generalized Memory Structure

• Large Data Storage repository.
• Structure is NOT dictated by what is stored in
  that memory (Content Independent).
• Several access mechanism modes exists to access
  its content .
• Any memory can be thought to be composed of
  several individually addressable blocks each of
  which contains some data (generic term) item.

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User Requirement/ Ideal View point of the
Computer Memory

• Should be Infinite Sized.
• Should possess High Speed of access.
• Should be of Low Cost .
• Has to be Reliable.
• Must be Expandable with little or no affect on
  the existing system configuration.
• Must be flexible adaptable to change in size as
  well as to compatibility with new emerging
  technologies.

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Classification of Memory

• Classification A ( Media Types).
• Electronic ROM, EPROM, Static RAM, Dynamic
  RAM, Flash , Memory Stick.
• Magnetic Hard Disk, Flex Disk, Tape, DAT.
• Optical CD-R/ -RW, DVD-R/RW, DVD-RAM, Blue-Ray
  DVD, HD DVD.
• Classification B ( Data Retention Property).
• Volatile. Electronic
• Non Volatile. Flash, Magnetic , Optical.
• Classification C ( Alterability Property).
• User Alterable. RAM, Flash, Disk, Tape, DAT,
  CD-RW, Blue-Ray / HD / Ordinary DVD-RW
• Non Alterable ROM, EPROM, Flash, CD, DVD.
• Classification D ( CPU Proximity
  Accessibility, Most System Relevant).
• Register. Electronic, Volatile, User
  Alterable.
• Cache. Electronic, Volatile, Transparent to
  User
• Main / Primary. Electronic, Volatile, User
  Alterable.
• Secondary ( Some External) . Flash, Magnetic
  Disks Tapes, Optical, Non Volatile, Some User
  Alterable.

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Peripheral Remote Devices

• Peripherals/ Peripheral Devices All those
  Devices that lie in the Periphery of the CPU. All
  Peripheral Devices are connected to the CPU
  through several Buses (as illustrated earlier)
  and are controlled by the CPU through some Device
  Driver program (s) part of the Operating
  System.
• Remote Devices Those which are far away from
  the current CPU/ Computer System connected
  through the Network Interface.

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Input Output Peripherals

• Helps to establish link between computer / cyber
  world Real World. Various forms of I/O
  Peripherals exists.
• Common Input Peripherals Key board, Mouse.
• Common Output Peripherals Video Monitor,
  Printer.

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Input Peripheral Devices and their Functions (
Architectural Aspects)

• These are employed to feed data , program,
  picture, commands to the Computer System. A few
  commonly used devices are the following
• Keyboard ( The earliest and still most commonly
  used Input Device). To type in Commands and/or
  Data Alphabets, Digits, Symbols etc.
• The Mouse Commands are given by clicking its
  left/right button. It works in a Graphic
  Environment where user is given option to select
  among several Options in a menu by moving mouse
  button on to that item and clicking on that.

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Output Peripherals and their Functions- 1

• Output Peripherals are responsible for providing
  some form of response/result to the user.
  Commonly used Output peripheral devices are
• Visual Display Unit (VDU) Screen / Monitor Is
  used to display the following
• Anything typed in via keyboard.
• The various menus available to the user.
• The response generated by the system to various
  user commands in some way.
• The result generated by running various programs/
  packages.

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Output Peripherals and their Functions - 2

• 2. Printers Used to produce printed Outputs /
  Hard Copy. Various types of printers
• Impact Printers Where there exists a physical
  printing Mechanism/ print head that strikes on
  the paper ink ribbon to make an impression on
  the Paper. These mostly print in Black . Examples
  of such printers are Dot Matrix , Line , Band
  etc.
• Non Impact Printers Here there exists no
  physical printing heads rather printing is done
  by electronic/electrostatic mechanism that
  regulate the flow of ink/toner which are electro
  statically deposited on the paper. These can
  print both in Monochrome (black) as well as in
  Color. Commonly used printers are Inkjet, Desk
  jet, Laser etc.
• Graphic Printers like Dot Matrix, Inkjet, Desk
  Jet, Laser can print both text as well as
  pictures while Line Printer, Band Printer can
  only print characters . But these are high speed
  rugged compared to graphic printers .

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Peripheral Interfaces - 1

• Most of the peripheral devices helps in
  establishing human interface to the computer
  System (mainly CPU Memory).
• Each of the peripheral differs in
  characteristics from each other as well as from
  the electronic parts (CPU Memory) in terms of
  electrical features and operating speed.
• Some kind of programs are required to control
  all the various peripherals (Device Drivers) .
• Users interact with any computer either by some
  command or alternately by mouse click . Hence
  some form of command interpreter or Graphic User
  interface GUI is needed .
• These device driver programs as well as Command
  Interpreter GUI forms part of the existing
  Operating System .

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Peripheral Interfaces - 2

• All peripherals must possess the following things
  
• a) An Electronic Peripheral Interface
  that helps to isolate the CPU Main Memory from
  the diverse world of peripherals.
• b) CPU Peripheral connectivity is
  established through the following components
• 1) Electronically addressable Command
  Register (Write Only).
• 2) Electronically addressable
  Status Register (Read Only).
• 3) Electronically addressable
  Local Data Buffer (Read/Write).

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BUS The Connection Gateway

• Group of Electrical Lines ( cables and/or PCB
  Tracks OR both ) performs a particular task in
  unition.
• Helps to connect the Different Components of
  any Computer System.

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CPU External World Connectivity - 1

• 1) CPU must be able to address each
  device interface as well as each memory location.
  This Address is sent via a group of electrical
  lines / PCB Tracks termed as the Address bus.
• 2) CPU sends / receives data to /
  from the device interface memory through a
  separate group of lines termed as Data Bus.
• 3) CPU sends Command to / or reads
  Device Status from the device interface / memory
  via a 3rd group of lines known as the Control
  Bus.

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The Different Buses

• Address Bus - Group of lines that is used to
  carry address information from the CPU to the
  concerned device(s). Address is one that helps
  the CPU to select one among many devices. Hence
  it is unidirectional.
• Data Bus - The group of lines used to carry
  data/information from the device to CPU vice
  versa. It is always bi-directional.
• Control Bus The group of lines that enables the
  CPU to control various activities by sending
  appropriate commands as well as monitor status of
  the concerned device e.g. Read Signal, Write
  Signal, Status Set Signal.
• Each bus consists of a number of lines, which is
  represented in a compact manner.

Bi Directional Bus composed of 32 Lines
32
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Memory Bus I/O Bus

• As has already been mentioned , Peripherals
  presents a much larger diverse interface scenario
  than the Memory.
• The entire Memory hierarchy interacts with the
  CPU through some pre-specified protocol.
• Whereas, large diverse nature of Peripheral
  Interfaces demands a much larger variety of
  interface protocols .
• This demands different set of Buses , namely,
  I/O Bus and Memory Bus to connect peripherals and
  Memory respectively with the CPU.
• However, any type of BUS, in principle , must
  essentially compose of ADDRESS, DATA CONTROL
  Buses only differing in signal level layout.

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Oversimplified Bus Level Organization