The Basic Features of a Computer

1
The Basic Features 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, Audio, Video with reasonably high
  access speed Information Bank.
• Communication Gateway Link to the World.

2
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.

3
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
• 4a) Arranging Data Items like
  preparation of merit list.
• 4b) Manipulating Pictures
  Graphics.
• 4c) Multimedia applications (
  Audio, Video, Graphics, Video)
• 4d) Create, format, send receive
  messages of various forms.

4
Computer Components 1
C.P.U.

• 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 processing tools i.e. the instructions
  available for processing . These instructions
  constitute any program framed to accomplish any
  kind of processing.
• Ability to properly sequence the processing
  steps / instructions to achieve the desired
  result Control.
• The above three are closely linked together
  hence can all be encapsulated into the C.P.U.
  Central Processing Unit.

5
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 ( To be illustrated in due course ).

6
The CPU Components

Register
ALU
Control Unit
7
Computer Components 2
The Memory

• Memory Essential to create any form of
  Information Bank/ Data Repository.
• Wide range types of Memory Storage Media
  are available/ in use now a days .

8
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 item(s).

9
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.
• 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, DVD-RW
• Non Alterable ROM, EPROM, 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 . Flash, Magnetic Disks Tapes,
  Optical, Non Volatile, Some User Alterable.

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The Typical Memory Hierarchy

Electronic Mostly Volatile
GPRs
SIZE
On Chip CACHE
COST SPEED
Off Chip Cache
Main/ Primary / Physical Memory
Fixed Secondary Memory Magnetic Disk Non
Volatile
Removable Secondary Mag.Tapes, Electronic
Flash, Optical CD_ROM, DVDs Non Volatile
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System Programmers view point of the Computer
Memory

• The actual Physical Memory is finite sized like a
  large , fixed size , one dimensional column
  vector.
• Any user should not be affected by the available
  / existing memory capacity. Any one user
  processs space requirement may exceed the total
  available / existing memory capacity but still
  can be run in the system with no marked
  degradation in response time / performance.
• There will be more than one user process
  together with the operating system resident in
  the existing memory at any point of time.
• The existing memory capacity, if enhanced , will
  not force a regeneration of the system but rather
  will improve response time.

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The Actual Memory Levels ( Look Through
Configuration

CPU
COST SPEED
On Chip MMU
SIZE
Cache On Chip Off Chip
Each Hierarchical Level represents a Higher Speed
Version that contains some portion of its
immediate Next Hierarchical Level
Cache _ Main Interface
Main / Physical Memory
Secondary Memory Associated Interface
14
The Memory Hierarchy

• MMU Memory Management Unit acts as the
  interface interconnection block between the CPU
  and the Memory System.It helps to manage the
  finite sized main memory in such a way that it
  appears to the user as an Infinite Sized High
  Speed Memory.
• Cache Memory A high speed partly content
  addressable memory which represents a high speed
  window of the Main Memory. Its typical size
  happens to be 256 KB. CPU normally accesses the
  Main Memory through the Cache Memory (look
  through configuration). It does not add up to the
  main memory space in any way.We shall however
  initially assume that this Cache Memory is
  transparent till it is formally introduced later.

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Basic Read Write Memory (RWM) Organization
Data In
Input Buffer
WRITE
Addressable Unit / Block 1
S E L E C T I O N
ADDRESS
IN DATA BUS
Addressable Unit / Block i
Addressable Unit / Block N
OUT DATA BUS
Output Buffer
READ
Data Out
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Features of an Electronic Memory
17
An Electronic Memory Location Its Content

• Memory is shown here as a group of Mail Boxes
  actually a group of 8 (Eight) electronic storage
  cells addressable together.
• Each byte can assume one of 256 different values
  since using 8 bits one can represent 2 8 256
  different values.
• Each location has a unique numeric identifier
  which denotes its address. Note the addresses
  shown in the previous slide e.g. box. No. 0 , 1,
  2 etc.
• Each address can hold any one of 256 possible
  values as data as has been depicted.

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An Electronic Memory Location (an Inside View)

• Each Location of any Electronic Memory (usually
  one byte / 8 Bits) can be viewed as a parallel
  in parallel-out (PIPO) Register composed of 8
  no. of D F/Fs.
• The Addressing Mechanism is implemented using
  Address Decoder.
• The Data Read Signal is actually achieved
  through Output Enable (OE) signal .
• The Data Write Signal represents the Write Clock
  / the Clock of the D F/Fs (all tied together) .

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Byte Organized Memory Vs. Multi Byte CPU

• Main Memory is byte organized (normally).
• Modern day CPUs can handle multi byte words
  (usually integral multiples) say 4 bytes.
• In such a case one of the two following storage
  pattern is followed
• 1) Little Endian Lower Memory Address holds
  lower order byte. Intel Convention .
• 2) Big Endian Lower Memory Address holds
  Higher Order byte.

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Storage Pattern of n X 8 bit ( n an integer)
Data, in Byte Organized Memory

• Example n 4 i.e. 32 bit Data
• 32 bit Data Word A2 24 3C 4B 8 Hex Digits
• 4 byte Memory Block starting from A000 0000 (32
  bit Address)
• Address Content in Hex
• in Hex (Little Endian) ( Big
  Endian )
• --------------------------------------------------
  --------------------
• A000 0000 4B
  A2
• --------------------------------------------------
  --------------------
• A000 0001 3C
  2 4
• --------------------------------------------------
  --------------------
• A000 0002 24
  3C
• --------------------------------------------------
  --------------------
• A000 0003 A2
  4B
• --------------------------------------------------
  --------------------

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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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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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Typical Bus Level Organization
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Typical WRITE Sequence CPU Storing Data to a
Memory Location/ Sending Data / Command to
Device Interface Register(s)

• Say CPU wants to Write Decimal Value 11 into
  location / address 2 (Decimal) .
• CPU sends (floats) 2 via its Address Bus. This
  value 2 coming via address bus will select the
  Memory Location/ Device Interface Buffer location
  whose address happens to be 2 (Decimal).
• CPU next sends value 11 via its Data Bus . The
  CPU also asserts the Write Signal through its
  control bus at the same time. This Write Signal
  will write 11 (value sent via data bus) in the
  location already selected by the address bus (2
  here).
• CPU waits for the Acknowledgement signal via its
  Control Bus, from the written place before
  proceeding with the next write. (necessary for
  slow devices)

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Typical READ / FETCH Sequence CPU Loading Data
from Memory / Device Interface Registers OR
Fetching Instruction from Memory

• Say CPU wants to Read from the location whose
  address happens to be 3 (Decimal) or 0000 0000
  0000 0011 in 16 bit Binary.
• CPU sends (floats) 3 via its Address Bus. This
  value 3 coming via address bus will select the
  Memory Location/ Device Buffer Location whose
  address happens to be 3.
• The CPU also asserts the Read Signal through
  its Control Bus at the same time. This Read
  Signal will read i.e. make available on the
  data bus the value/ data content of the location
  already selected by the address bus (3 here).
• CPU next waits for the READY signal sent through
  its Control Bus from the concerned Memory
  Location/ Device interface buffer (a must for
  slow device) before probing its Data Bus and then
  it must store the data existing on the Data Bus
  (READ from the location 3 ) into a relevant
  storage place lying inside it CPUs local memory
  store . This local memory store inside any CPU
  is termed as REGISTER. Several Registers may
  exist inside any CPU. Some of them are special
  purpose while others are general purpose
  registers GPRs .

31
Computer Architecture Operating System

• Architecture Functions of the different
  hardware / organizational blocks of a Computer
  System.
• - CPU.
• - Memory ( Main Secondary).
• - Input Output Peripherals.
• Operating System A System Software that helps
  all type of users to operate a computer System.

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The Functions of the CPU

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

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The CPU Performance Parameters - 1

• N.B All the activities of any CPU are being
  carried out by executing some machine level /low
  level instruction.
• 1. CPU Speed Each 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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The Functions of Electronic Physical Memory - 1

• Acts as the brain of the Computer System.
  Functions as the only accessible storage for the
  CPU i.e. anything everything MUST first be
  brought in the Physical Memory before it can be
  accessed by the CPU.
• Stores inputted commands, data, program as well
  as intermediate final results.
• CPU stores data into it and retrieves data as
  well as Instructions from it .
• It is composed of several locations , each
  location size is normally one byte or its integer
  multiple . (1 byte 8 Bits 1 Character).
• It is finite sized ( typical capacity 512
  Mbytes(MB) ), Electronic , Volatile and Random
  Access Time taken to access any location is
  identical and relatively costly.

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The Functions of Electronic Physical Memory - 2

• 6. The main memory can be viewed as a very
  large sized , one dimensional matrix /array, a
  column vector. Time taken to access any
  element/location happens to be the same .
• 7. Some part of it is non volatile (Read Only
  Memory ROM ) some of it is Read Write Memory
  RWM commonly termed as RAM (Random Access
  Memory).
• Now a days slow Dynamic Main Memory is connected
  to the CPU through a high speed electronic Memory
  known as the Cache Memory as well as the Memory
  Management Unit (MMU).
• The Cache as well as the MMU helps to interface
  the higher word sized, high speed CPU with the
  byte wide, low speed Main Memory.

37
The Secondary Memory Functions
(InputLoadOutput Store)

• Acts as the Back up Store of the Computer System.
• Can be viewed as a Filing Cabinet for storing
  Data , Program by the CPU Backbone of the File
  System in any computer.
• It represents the Non Volatile form of storage.
• As compared to main memory the secondary memory
  represents slow, Large Capacity ( Theoretically
  infinite Helps in building Virtual Memory) ,
  relatively cheap medias like the following
• Magnetic Medias like Fixed / Winchester Hard
  Disks or Removable Media like Floppy, Tape , DAT
  etc
• Removable Optical Medias like CD /DVD ROMs (
  Read only) , CD/DVD-R (Recordable in a place
  once only ), CD/DVD-RW (Rewritables)
• Removable Electronic Non Volatile Compact Memory
  like Memory Sticks, Pen Drives Flash Memory .
• It represents infinite capacity storage because
  of the existence of removable media components.
  

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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).
• Remote Devices Those which are far away from
  the current CPU/ Computer System connected
  through the Network Interface.

39
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 .

42
The Actual Scenario - 1

• Each every CPU works by executing some
  pre-written , stored programs . Some of these
  programs like Editor, Operating System,
  Translator( Compiler/Assembler), Linking Loaders
  System Programs are not written by the
  ordinary users but are already written and
  maintained by the System Programmer(s).Other
  Programs are termed as Application Packages.
• These System Programs as well as some
  application packages are preserved as executable
  files in the secondary memory / Non Volatile
  Store.
• However , in order to be executed, any
  executable file will have to be brought into the
  volatile main memory.
• Power on self test Program as well as some of
  the device driver programs like Keyboard Driver ,
  Display Driver and Disk Read/Write Drivers are
  needed immediately after power on , hence these
  needs to be available in some non volatile,
  unalterable section of the electronic main memory
  ROM.

43
The Actual Scenario - 2

• In order to execute any program CPU has to
  execute its instructions stored in main memory
  one by one.
• Before execution CPU will have to read/ fetch
  the instructions inside some of its register
  from main memory.
• Any activity inside the Computer System will have
  to be initiated by the CPU in accordance with an
  instruction execution.
• Respond to any user command , peripheral control
  communications are done by the various modules
  of the Operating System O.S. program.
• The Operating System modules initially starts
  running and subsequently are invoked from within
  some user program by system call (via software
  interrupt) , exceptions OR through
  device/hardware interrupts.