Computer Architecture

1
Computer Architecture Operating System

• Architecture Functions of the different
  hardware / organizational blocks of a Computer
  System. Primarily described by its Instruction
  Set Architecture ISA that consists of
• - CPU Processing Capability, Speed etc.
• - Memory / Main Memory.
• - Assembly Language Instruction Set of the
  CPU.
• - Associated Operands.
• Operating System A System Software that helps
  all type of users to operate a computer System.

2
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 a
  high degree of accuracy at a pretty high speed.
• Storage of huge amount of information with
  reasonably high access speed (Information Bank).
• Communication Gateway Link to the World.

3
Computer Vs. Electronic Organizer

• User programmability i.e. any user can write a
  program in a computer to tune/control the way
  computation is done . 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.
• Connectivity to other computers and various
  peripherals is readily available in any computer.
• One can easily upgrade any Computer by installing
  new packages / connecting more upgraded
  peripherals, enhancing memory etc.

4
Data Processing Activity of any Typical Computer
(done by executing some program)

• Ordinary Arithmetic Operations.
• Logical Operations like comparing two items.
• Special type of arithmetic operations like
  addition of two very very large integers
  (achieved through Special Application Programs)
  .
• Manipulating floating point numbers.
• Sorting of Data like preparation of merit list.
• Manipulating Pictures Graphics.
• Multimedia ( Audio, Video, Graphics , Video Games
  etc.) Manipulations.
• Ability to create, format, send receive
  messages.

5
The Typical Computer Organization The
Constituent Hardware Blocks
6
Computer Organization Various Parts - 1

• Peripherals/ Peripheral Devices All those
  Devices that lie in the Periphery of the CPU. All
  Peripheral Devices are connected to the CPU by
  some way and are controlled by the CPU through
  some system program.
• Remote Devices Those which are far away from
  the current CPU/ Computer System possibly
  connected through Network Not shown here .

7
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.

8
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.

9
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 .

10
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
• CD /DVD ROMs ( Read only) , CD/DVD-R
  (Recordable in a place once only ), CD/DVD-RW
  (Rewritables) all removable.
• It represents infinite capacity storage because
  of the existence of removable media components.
  

11
The Functions of Main/ Physical Memory

• Acts as the brain of the Computer System.
• 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 256
  Mbytes(MB) ), Electronic , Volatile and Random
  Access Time taken to access any location is
  identical and relatively costly.
• 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 .
• 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 Main Memory is connected to the CPU
  through a high speed electronic Memory known as
  the Cache Memory.

12
Features of an Electronic Memory
13
An Electronic Memory Location Its Content

• Memory is shown here as a Group of Mail Boxes
  i.e. each location is a Mail Box used to hold a
  byte ( 8 bits ) of data .
• Lets assume each binary digit ( one bit ) is a
  single mail envelopes hence each location / mail
  box can hold eight (8) bits or eight different
  envelopes .
• Each byte can assume one of 256 different values
  since using 8 bits one can represent 2 8 256
  different values.
• Each mail box 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 values as
  data as has been depicted.

14
An Electronic Memory Location (an Inside View)

• Each Location of any Electronic Memory (usually
  one byte / 8 Bits) is actually implemented by
  using 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) .

15
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.

16
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
• --------------------------------------------------
  --------------------

17
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

18
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 .

19
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).

20
Computer Organization 2 (Slightly Detailed View)
21
Computer Organization (Other Parts - 1)

• 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.

22
Computer Organization (Other Parts - 2)

• DMA Direct Memory Access Controllers used by
  some peripherals to Interact with the Memory
  bypassing the CPU (sometimes required for very
  high speed access of memory).
• I/O Controllers Acts as intermediary /
  interface between the CPU and diverse types of
  peripheral devices enabling the CPU to treat
  every peripheral device in the same way.
• N.B (1) The Secondary Storage Peripherals are
  also termed as I/O Peripherals.
• (2) Each of these above controllers
  does possess some form of local memory /
  registers termed as buffers as well as local
  controllers.
• (3) DMA happens to be one particular
  type of I/O Interface Mechanism .

23
Some Key Observations - 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 .

24
Some Key Observation - 2

• All peripherals must possess the following things
  
• a) An Electronic Peripheral Interface.
• b) Each Peripheral Interface must
  possess the following
• 1) Electronically addressable
  Command Register (Write Only).
• 2) Electronically addressable
  Status Register (Read Only).
• 3) Electronically addressable
  Local Store / Buffer (Read/Write).

25
Some Key Observation - 3

• CPU External World (Memory / Peripheral )
  Interface
• 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.

26
The Computer Organization as we See
27
The CPU-External World Connectivity

• 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
28
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)

29
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 .

30
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.

31
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.