MODULE-1(a) - Basic-Structure-of-Computers.pptx

Computer Organization
and
Architecture
1
Carl Hamacher, Zvonko Vranesic, Safwat
Zaky,
Computer Organization, 5th
Edition,
Tata McGraw Hill, 2002.

Module-1
Basic Structure of Computers
2

Computer Types
3
 A digital computer, or simply, a computer is a
fast electronic calculating machine that
accepts digitized input information,
processes it according to a list of
internally stored instructions, and
produces the resulting output
information.
 The list of instructions is called a
computer program, and the internal
storage is called computer memory.

Computer Types..
4
 Many types of computers exist that differ
widely in size, cost, computational power,
and intended use.
 Four general categories
 Personal Computers
 Servers and Enterprise Systems
 Supercomputers and Grid Computers
 Embedded Computers

Computer Types..
5
 Personal computers have achieved
widespread use in homes, educational
institutions, and business and
engineering office settings, primarily
for dedicated individual use.
 They support a variety of applications
such as general computation,
document preparation, computer-aided
design, audiovisual entertainment,
interpersonal communication, and
Internet browsing.

Computer Types..
6
 A number of classifications are used for personal
computers.
 Desktop computers serve general needs and fit
within a typical personal workspace.
 Workstation computers offer higher computational
capacity and more powerful graphical display
capabilities for engineering and scientific work.
 Portable and Notebook computers provide the basic
features of a personal computer in a smaller
lightweight package.
 They can operate on batteries to provide mobility.

Computer Types..
8
 Servers and Enterprise systems are large
computers that are meant to be shared by
a potentially large number of users who
access them from some form of personal
computer over a public or private
network.
 Such computers may host large
databases and provide information
processing for a government agency or
a commercial organization.

Computer Types..
10
 Supercomputers and Grid computers
normally offer the highest performance.
 They are the most expensive and physically
the largest category of computers.
 Supercomputers are used for the highly
demanding computations needed in
weather forecasting, engineering design
and simulation, and scientific work.
 They have a high cost.

Computer Types..
12
 Grid computers provide a more cost-
effective alternative.
 They combine a large number of personal
computers and disk storage units in a physically
distributed high-speed network, called a grid,
which is managed as a coordinated computing
resource.
 By evenly distributing the computational
workload across the grid, it is possible to
achieve high performance on large
applications ranging from numerical
computation to information searching.

Computer Types..
14
 Embedded computers are integrated into
a larger device or system in order to
automatically monitor and control a
physical process or environment.
 They are used for a specific purpose
rather than for general processing
tasks.
 Typical applications include industrial
and home automation, appliances,
telecommunication products and

Computer Types..
 There is an emerging trend in access to
computing facilities, known as cloud
computing.
 Personal computer users access widely
distributed computing and storage server
resources for individual, independent,
computing needs.
 The Internet provides the
necessary communication facility.
 Cloud hardware and software service
providers operate as a utility, charging on a
use
16

Functional Units
19
Figure 1.1. Basic functional units of a computer.
I/O Processor
Output
Memory
Input
Arithmetic
and
logic
Control

Functional Units..
20
 A computer consists of five functionally
independent main parts: input, memory, arithmetic
and logic, output, and control units.
 The input unit accepts coded information from
human operators using devices such as
keyboards, or from other computers over digital
communication lines.
 The information received is stored in the
computer’s memory, either for later use or to be
processed immediately by the arithmetic and
logic unit.
 The processing steps are specified by a program
that is also stored in the memory.

Functional Units..
21
 Finally, the results are sent back to the
outside world through the output unit.
 All of these actions are coordinated by
the control unit.
 The arithmetic and logic circuits, in
conjunction with the main control circuits,
are referred to as the processor.
 Input and output equipment is often
collectively referred to as the input-output
(I/O) unit.

Information handled by a
computer
22
 Instructio
n
 Data

computer..
23
 Instructions, or machine instructions,
are explicit commands that
 Govern the transfer of information within a
computer as well as between the computer
and its I/O devices
 Specify the arithmetic and logic operations to
be performed

computer..
24
 A program is a list of instructions
which performs a task.
 Programs are stored in the memory.
 The processor fetches the program
instructions from the memory, one after
another, and performs the desired operations.
 The computer is controlled by the stored
program, except for possible external
interruption by an operator or by I/O devices
connected to it.

computer..
25
 Data are numbers and characters that
are used as operands by the
instructions.
 Data are also stored in the memory.

computer..
26
 The information handled by a computer
must be encoded in a suitable format.
 Most present-day hardware employs
digital circuits that have only two stable
states, ON and OFF.
 Each instruction, number, or character is
encoded as a string of binary digits called
bits, each having one of two possible
values, 0 or 1.

Input Unit
27
 Computers accept coded information
through input units.
 The most common input device is the
keyboard.
 Whenever a key is pressed, the corresponding
letter or digit is automatically translated into its
corresponding binary code and transmitted to
the processor.
 Other kinds of input devices – mouse,
joystick, trackball, touchpad, microphone,
camera.

Memory Unit
28
 The function of the memory unit is to
store programs and data.
 There are two classes of storage
 Primary
 Secondary

Memory Unit..
29
 Primary memory, also called main memory, is a fast
memory that operates at electronic speeds.
 Programs must be stored in this memory while they are
being executed.
 It consists of a large number of semiconductor
storage
cells, each capable of storing one bit of information.
 They are handled in groups of fixed size called words.
 One word can be stored or retrieved in one basic
operation.
 The number of bits in each word is referred to as the word
length
of the computer, typically 16, 32, or 64 bits.

Memory Unit..
30
 To provide easy access to any word in the
memory, a distinct address is associated
with each word location.
 Addresses are consecutive numbers,
starting from 0, that identify successive
locations.
 A particular word is accessed by specifying
its address and issuing a control
command to the memory that starts the
storage or retrieval process.

Memory Unit..
31
 Memory in which any location can be
accessed in a short and fixed amount of
time after specifying its address is called
a random-access memory (RAM).
 The time required to access one word
is called the memory access time.
 It typically ranges from a few nanoseconds (ns)
to about 100 ns for modern RAM units.

Memory Unit..
32
 The memory is normally implemented
as a memory hierarchy of three or four
levels of RAM units with different
speeds and sizes.
 The small, fast RAM units are called
cache.
 Tightly coupled with the processor
 Contained on the same chip to achieve
high performance
 Largest and slowest unit is referred to

Memory Unit..
33
 Although primary memory is essential,
it tends to be expensive and does not
retain information when power is
turned off.

Memory Unit..
34
 Secondary storage is used when large
amounts of data and many programs
have to be stored.
 Particularly for information that is
accessed in frequently.
 Access times for secondary storage
are longer than for primary memory.
 Examples - magnetic disks, optical
disks
(DVD and CD), and flash memory

Arithmetic and Logic Unit
(ALU)
35
 Most computer operations are
executed in ALU of the processor.
 Any arithmetic or logic operation, such as
addition, subtraction, multiplication,
division, or comparison of numbers, is
initiated by bringing the required
operands into the processor, where the
operation is performed by the ALU.

Arithmetic and Logic Unit
(ALU)..
36
 For example, if two numbers located in the memory
are to be added, they are brought into the processor,
and the addition is carried out by the ALU.
 The sum may then be stored in the memory or retained in
the
processor for immediate use.
 When operands are brought into the processor, they
are stored in high-speed storage elements called
registers.
 Each register can store one word of data.
 Access times to registers are even shorter than access
times to the cache unit on the processor chip.

Output Unit
37
 It sends processed results to the outside world.
 Example – printer
 Most printers employ either photocopying techniques, as in
laser printers, or ink jet streams. Such printers may
generate output at speeds of 20 or more pages per minute.
 Some units, such as graphic displays, provide both
an output function, showing text and graphics, and
an input function, through touchscreen capability.
 The dual role of such units is the reason for using the
single name input/output (I/O) unit in many cases.

Control Unit
38
 The memory, arithmetic and logic, and
I/O units store and process
information and perform input and
output operations.
 The control unit coordinates the
operation of different units in the
computer.
 The control unit is effectively the nerve
center that sends control signals to other
units and senses their states.

Control Unit..
 I/O transfers, consisting of input and
output operations, are controlled by
instructions of I/O programs.
 Control circuits are responsible for
generating the timing signals that govern
the transfers and determine when a given
action is to take place.
 Data transfers between the processor and
the memory are also managed by the
control
unit through timing 39

Control Unit..
 Much of the control circuitry is
physically distributed throughout the
computer.
 A large set of control lines (wires) carries
the signals used for timing and
synchronization of events in all units.
40

Summary
The operation of a computer can be summarized as
follows:
 The computer accepts information in the form of
programs and data through an input unit and stores
it in the memory.
 Information stored in the memory is fetched under
program control into an arithmetic and logic unit,
where it is processed.
 Processed information leaves the computer
through an output unit.
 All activities in the computer are directed by the
control
unit
.
41

Review
43
 The activity in a computer is governed
by instructions.
 To perform a given task, an appropriate
program consisting of a list of instructions is
stored in the memory.
 Individual instructions are brought from the
memory into the processor, which executes
the specified operations.
 Data to be used as instruction operands are
also stored in the memory.

A Typical Instruction
44
Add LOCA, R0
 Add the operand at memory location LOCA to
the operand in a register R0 in the processor.
 Place the sum into register R0.
 The original contents of LOCA are preserved.
 The original contents of R0 are overwritten.
 Several steps
 Instruction is fetched from the memory into the
processor
 Operand at LOCA is fetched and added to the
contents of R0
 The resulting sum is stored in register R0

Separate Memory Access
and ALU Operation
45
 Add LOCA, R0 combines a memory
access operation with an ALU
operation.
 In most modern computers, these
two types of operations are
performed by separate
instructions for improving
performance

Separate Memory Access
and ALU Operation..
46
Load
LOCA, R1 Add
R1, R0
 The first instruction transfers the
contents of memory location LOCA into
register R1.
 The second instruction adds the contents of
register R1 and R0 and places the sum into

Connection Between the
Processor and the Memory
47
Processor
Memory
PC
IR
MDR
Control
ALU
R 0
R 1
R
n - 1
MAR
n general purpose
registers
Figure 1.2. Connections between the processor and the memory.

Registers
48
 Instruction register (IR)
 Hold the instruction that is currently being executed
 Program counter (PC)
 Keeps track of the execution of a program
 It contains the address of the next instruction to be
fetched and executed
 General-purpose register (R0 – Rn-1)
 Memory address register (MAR)
 Holds the address of the memory location to be accessed
 Memory data register (MDR)
 Contains the data to be written into or read out of the
addressed
location

Typical Operating Steps
49
 Programs reside in the memory through
input devices
 PC is set to point to the first instruction
 The contents of PC are transferred to MAR
 A Read control signal is sent to the
memory
 The first instruction is read out and
loaded into MDR
 The contents of MDR are transferred to
IR
 Decode and execute the instruction

Typical Operating Steps..
50
 Get operands for ALU
 General-purpose register
 Memory (address to MAR – Read – MDR to ALU)
 Perform operation in ALU
 Store the result back
 To general-purpose register
 To memory (address to MAR, result to MDR –
Write)
 During the execution, PC is
incremented to the next
instruction

Typical Operating Steps..
51
 In addition to transferring data between
the memory and the processor, the
computer accepts data from input
devices and sends data to output
devices.
 Thus, some machine instructions are
provided for the purpose of handling
I/O transfers.

Interrupt
so that the program may continue from where it was
 Normal execution of programs may be preempted
if
some device requires urgent servicing.
 The device raises an interrupt signal.
 An interrupt is a request from an I/O device for
service by the processor.
 The processor provides the requested service
by executing an appropriate Interrupt-service
routine.
 May alter the internal state of the processor
 Its state must be saved before servicing the interrupt
 The contents of PC, general-purpose registers,
and some control information are stored in
52

Example
53
List the steps needed to execute the
machine instruction
Add LOCA,R0
in terms of transfers between the
components shown in Figure 1.2 and
some simple control commands.
Assume that the instruction itself is
stored in the memory at location INSTR
and that this address is initially in
register PC.

Example
54
 Transfer the contents of register PC to
register MAR
 Issue a Read command to memory, and
then wait until it has transferred the
requested word into register MDR
 Transfer the instruction from MDR into IR
and decode it
 Transfer the address LOCA from IR to MAR
 Issue a Read command and wait until MDR
is loaded

Example
55
 Transfer contents of MDR to the ALU
 Transfer contents of R0 to the ALU
 Perform addition of the two operands in the
ALU and transfer result into R0
 Transfer contents of PC to ALU
 Add 1 to operand in ALU and
transfer incremented address to
PC

Example
56
List the steps needed to execute the
machine instruction
Add R1,R2,R3
in terms of transfers between the
components shown in Figure 1.2 and
some simple control commands.
Assume that the instruction itself is
stored in the memory at location INSTR
and that this address is initially in
register PC.

Example
 Transfer the contents of register PC to
register MAR
 Issue a Read command to memory, and
then wait until it has transferred the
requested word into register MDR
 Transfer the instruction from MDR into IR
and decode it
 Transfer contents of R1 and R2 to the
ALU
 Perform addition of two operands in the
ALU and transfer answer into R3
57

Example
58
 Transfer contents of PC to ALU
 Add 1 to operand in ALU and
transfer incremented address to
PC

Bus Structures
59
 There are many ways to connect
different parts inside a computer
together.
 When a word of data is transferred
between units, all its bits are transferred
in parallel, that is, the bits are transferred
simultaneously over many wires, or lines,
one bit per line
 A group of lines that serves as a
connecting path for several devices is

Bus Structures..
60
 Single-
bus

Bus Structures..
61
 The main virtue of the single-bus
structure is its low cost and its flexibility
for attaching peripheral devices.
 Systems that contain multiple buses
achieve more concurrency in operations
 Allow two or more transfers to be carried
out at the same time
 This leads to better performance but at
an increased cost.

Speed Issue
 Different devices have different transfer/operating
speed.
 Some electromechanical devices, such as keyboards
and printers, are relatively slow
 Magnetic or optical disks are considerably faster
 Memory and processor units operate at electronic
speeds -
fastest
 If the speed of bus is bounded by the slowest
device connected to it, the efficiency will be very
low.
 How to solve this?
 A common approach – use buffer registers
 Hold the information during transfers
I/O
devices.
62

Software
 System software is a collection of
programs that are executed as needed
to perform functions:
 Receiving and interpreting user commands
 Entering and editing application programs and
storing them as files in secondary storage
devices
 Managing the storage and retrieval of
files in secondary storage devices
 Running standard application programs such
as word processors, spreadsheets, or
data supplied by the 63

Software..
64
 Controlling I/O units to receive input
information and produce output results
 Translating programs from source form
prepared by the user into object form
consisting of machine instructions
 Linking and running user-written application
programs with existing standard library
routines, such as numerical computation
packages

Software..
65
 System software is responsible for the coordination
of all
activities in a computing system.
 Application programs are usually written in a high-
level programming language, such as C, C++, Java,
or Fortran
 Independent of the particular computer used to
execute the program.
 A programmer using a high-level language need
not
know the details of machine program instructions.
 Compiler translates the high-level language program
into a suitable machine language program

Software..
66
 Text editor - used for entering and
editing application programs.
 File - a sequence of alphanumeric characters
or binary data that is stored in memory or in
secondary storage.
 Operating system - a large program, or
actually a collection of routines, that is used
to control the sharing of and interaction
among various computer units as they
execute application programs.

Software..
67
 Consider a system with one processor, one
disk, and one printer.
 Assume that the application program has
been compiled from a high-level language
form into a machine language form and
stored on the disk.

Performance
70
 The most important measure of the
performance a computer is how quickly it
can execute programs.
 Three factors affect performance:
 Hardware design
 Instruction set
 Compiler

Performance..
72
 To discuss the performance of the
processor, we should consider only the
periods during which the processor is
active.
 These are the periods labelled Program and
OS routines in Figure 1.4.
 Sum of these periods is referred as the
processor time needed to execute the
program.

Performance..
 Processor time to execute a program depends on the
hardware
involved in the execution of individual machine
instructions.
Main
memory Processor
Bus
73
Cache
memory
Figure 1.5. The processor cache.

Performance..
74
 At the start of execution, all program instructions
and the
required data are stored in the main memory.
 As execution proceeds, instructions are fetched one
by one over the bus into the processor, and a copy
is placed in the cache.
 When the execution of an instruction calls for data
located in the main memory, the data are fetched
and a copy is placed in the cache.
 Later, if the same instruction or data item is
needed a second time, it is read directly from the
cache.

Performance..
75
 The processor and a relatively small cache
memory can be fabricated on a single
integrated circuit chip.
 A program will be executed faster if the
movement of instructions and data between
the main memory and the processor is
minimized, which is achieved by using the
cache.

Processor Clock
76
 Processor circuits are controlled by a
timing signal called a clock.
 The clock defines regular time
intervals, called clock cycles.
 The execution of each instruction is
divided into several steps, each of which
completes in one clock cycle.
 Length of one clock cycle is denoted as P
 Hertz – cycles per second

Basic Performance Equation
 T – processor time required to execute a program that has
been
prepared in high-level language
 N – number of actual machine language instructions
needed to complete the execution
 S – average number of basic steps needed to execute one
machine instruction. Each step completes in one clock
cycle
 R – clock rate
 Note: these are not independent to each other
T 
N  S
R
How to improve T?
78

Basic Performance Equation
79
 Lesser the value of T, higher the
performance.
 Reducing T means reducing N and S,
and increasing R
 The value of N is reduced if the source
program is compiled into fewer machine
instructions.
 The value of S is reduced if instructions
have a smaller number of basic steps to
perform or if the execution of instructions
is overlapped.
 Using a higher-frequency clock increases
the value or R, which means that the time

MODULE-1(a) - Basic-Structure-of-Computers.pptx

More Related Content

Similar to MODULE-1(a) - Basic-Structure-of-Computers.pptx

More from ssuser15dddf

Recently uploaded

MODULE-1(a) - Basic-Structure-of-Computers.pptx