UNIT1

COMPUTER ORGANIZATION AND

ARCHITECTURE(CSEN2011)

Prof Srinivas Prasad

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 Text/Reference Books
TextBooks:
1. M. Morris Mano, Computer System
Architecture, 3/e, Pearson education,
2008
References:
1. Carl Hamacher, Zvonko Vranesic,
Safwat Zaky, Computer Organization,5/e,
McGraw Hill,2001
2. John P. Hayes, Computer Architecture
and Organization, 3/e, McGraw Hill,
1998.
3. William Stallings, Computer
Organization and Architecture, 6/e,
Pearson PHI, 2012.
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– Computer performance has been
increasing phenomenally over the last
five decades.
– Brought out by Moore’s Law:
● Transistors per square inch roughly double
every eighteen months.
– Moore’s law is not exactly a law:
● But, has held good for nearly 50 years.

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 Classification of Software
● Two broad categories:
1. Application Software
● Used to solve a specific problem.
● Editor, financial accounting, weather
forecasting, etc.
2. System Software
● Helps in running other programs.
● Compiler, operating system, etc.
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 Software
● A set of instructions that tells the computer
what to do
● Two main types of software
– Application software(Application Software
includes programs that do real work for user)
– System software(controls the hardware so that
application software can perform a task)

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System Software
Application Software
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 Computer Languages
● Machine Language
– Expressed in binary.
– Directly understood by the computer.
– Not portable; varies from one
machine type to another.
● Program written for one type of machine
will not run on another.
– Difficult to use in writing programs.
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 Assembly Language
● Mnemonic form of machine language.
– Easier to use as compared to machine language.
● For example, use “ADD” instead of “10110100”.
– Not portable (like machine language).
– Requires a translator program called assembler.

Assembly Machine
language Assembler language
program program
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 Contd.
● Assembly language is also
difficult to use in writing
programs.
– Requires many instructions to solve
a problem.
● Example: Find the average of
three numbers.
MOV A,X ; A=X
ADD A,Y ; A=A+Y In C,
ADD A,Z ; A=A+Z
DIV A,3 ; A=A/3 RES = (X + Y + Z) / 3
MOV RES,A ; RES = A

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 High-Level Language
● Machine language and assembly language are called low-level languages.

– They are closer to the machine.

– Difficult to use.
● High-level languages are easier to use.
– They are closer to the programmer.
– Examples:
● Fortran, Cobol, C, C++, Java.
– Requires an elaborate process of translation.
● Using a software called compiler.
– They are portable across platforms.

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 What is a Computer?
It is a machine which can accept data, process them,
and output results.

Central
Input Processing Output
Device Unit Device
(CPU)

Inside
Main Memory
the Box

Storage (Hard disk)

Programming and Data Structures 10

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● Input Device

– Keyboard, Mouse, Scanner, Digital Camera

● Output Device

– Monitor, Printer

● Storage Peripherals

– Magnetic Disks: hard disk, floppy disk

● Allows direct access

– Optical Disks: CDROM, CD-RW, DVD

● Allows direct access

– Flash Memory: pen drives

● Allows direct access

– Magnetic Tape: DAT

● Only sequential access

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Basics of Bus

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 Structure - Top Level

Peripherals Computer

Central Main
Processing Memory
Unit

Computer
Systems
Interconnection

Input
Output
Communication
lines
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 Structure - The CPU

CPU

Computer Arithmetic
Registers and
I/O
Login Unit
System CPU
Bus
Internal CPU
Memory Interconnection

Control
Unit

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 Structure - The Control Unit

Control Unit

CPU
Sequencing
ALU Login
Control
Internal
Unit
Bus
Control Unit
Registers Registers and
Decoders

Control
Memory

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Von Neumann architecture

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 How does a computer work?
● Main difference with a calculator.
– Stored program concept.
● What is a program?
– Set of instructions for carrying out a specific task.
● Where are programs stored?
– In secondary memory, when first created.
– Brought into main memory, during execution.

● Question: How are numbers stored internally ?

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 Digital Computers use Binary
Numbers!
● A digital computer is built out of tiny
electronic switches.
– For ease of manufacturing and reliability,
switches can be in one of two states, ON
and OFF.
– Switch can represent 0 and 1 (a digit in
the binary number system).
● A computer works based on the binary
number system. 18

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 Number System :: The Basics
● We are accustomed to using the so-called decimal number
system.
– Ten digits :: 0,1,2,3,4,5,6,7,8,9
– Every digit position has a weight which is a power of 10
(Called PV).
● Example:
– 234 = 2 x 102 + 3 x 101 + 4 x 100

250.67 = 2 x 102 + 5 x 101 + 0 x 100 +

6 x 10-1 + 7 x 10-2

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 Common Number Systems
Used by Used in
System Base Symbols humans? computers?

Decimal Yes No
10 0, 1, … 9
Binary No
2 0, 1 Yes
Octal No
8 0, 1, … 7 No
Hexa- No
decimal 16 0, 1, … 9, No
A, B, … F
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 Architecture vs. Organization
● Architecture:
– Also known as Instruction Set Architecture
(ISA)
– Programmer visible part of a processor:
instruction set, registers, addressing modes,
etc.
● Organization:
– High-level design: How many caches? How
many arithmetic and logic units? What type
of pipelining, control design, etc.
– Sometimes known as micro-architecture. 21
Basic building blocks of a CPU

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Cont…

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 Basic processor architecture
Address of the memory
location to be accessed

Memory

Address of the next Data to be read into or

instruction to be fetched read out of the current
and executed. location

MAR/AR MDR/DR
Control

PC R0

R1 General purpose
IR registers
ALU
Instruction that is R(n-1)
currently being
-

n general purpose
executed registers Processor

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Register Transfer and Micro
operations

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REGISTER TRANSFER AND MICROOPERATIONS

• Register Transfer Language

• Register Transfer

• Bus and Memory Transfers

• Arithmetic Microoperations

• Logic Microoperations

• Shift Microoperations

• Arithmetic Logic Shift Unit

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 SIMPLE DIGITAL SYSTEMS

● Combinational and sequential circuits can be used to create simple

digital systems.

● These are the low-level building blocks of a digital computer.

● Simple digital systems are frequently characterized in terms of

– the registers they contain, and
– the operations that they perform.

● Typically,
– What operations are performed on the data in the registers
– What information is passed between registers

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 Register Transfer Language

MICROOPERATIONS (1)

● The operations on the data in registers are called

microoperations.
● The functions built into registers are examples of
microoperations
– Shift
– Load
– Clear
– Increment
– …

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 Register Transfer Language

MICROOPERATION (2)

An elementary operation performed (during

one clock pulse), on the information stored
in one or more registers

Registers ALU
(R) (f)

R  f(R, R)

f: shift, load, clear, increment, add, subtract, complement,

and, or, xor, … 29
 Register Transfer Language

ORGANIZATION OF A DIGITAL SYSTEM

• Definition of the (internal) organization of a computer

- Set of registers and their functions

- Microoperations set

Set of allowable microoperations provided

by the organization of the computer

- Control signals that initiate the sequence of

microoperations (to perform the functions)

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 Register Transfer Language

REGISTER TRANSFER LEVEL

● Viewing a computer, or any digital system, in this way is

called the register transfer level

● This is because we’re focusing on

– The system’s registers
– The data transformations in them, and
– The data transfers between them.

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 Register Transfer Language

REGISTER TRANSFER LANGUAGE

● Rather than specifying a digital system in words, a specific

notation is used, register transfer language

● For any function of the computer, the register transfer

language can be used to describe the (sequence of)
microoperations

● Register transfer language(In

symbolic notation, it
is used to describe the micro-operations
transfer among registers.)
– A symbolic language
– A convenient tool for describing the internal organization of digital
computers
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– Can also be used to facilitate the design process of digital systems.
 Register Transfer Language

DESIGNATION OF REGISTERS

● Registers are designated by capital letters, sometimes

followed by numbers (e.g., A, R13, IR)
● Often the names indicate function:
– MAR - memory address register
– PC - program counter
– IR - instruction register

● Registers and their contents can be viewed and represented in

various ways
– A register can be viewed as a single entity:

MAR

– Registers may also be represented showing the bits of data they contain33
 Register Transfer Language

DESIGNATION OF REGISTERS

• Designation of a register
- a register
- portion of a register
- a bit of a register

• Common ways of drawing the block diagram of a register

Register Showing individual bits

R1 7 6 5 4 3 2 1 0
15 0 15 8 7 0
R2 PC(H) PC(L)
Numbering of bits Subfields

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 Register Transfer

REGISTER TRANSFER

● Copying the contents of one register to another is a register

transfer

● A register transfer is indicated as

R2  R1

– In this case the contents of register R2 are copied (loaded) into

register R1
– A simultaneous transfer of all bits from the source R1 to the
destination register R2, during one clock pulse
– Note that this is a non-destructive; i.e. the contents of R1 are not
altered by copying (loading) them to R2

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 Register Transfer

REGISTER TRANSFER

● A register transfer such as

R3  R5

Implies that the digital system has

– the data lines from the source register (R5) to the destination
register (R3)
– Parallel load in the destination register (R3)
– Control lines to perform the action

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 Register Transfer

CONTROL FUNCTIONS
● Often actions need to only occur if a certain condition is true
● This is similar to an “if” statement in a programming language
● In digital systems, this is often done via a control signal, called
a control function
– If the signal is 1, the action takes place
● This is represented as:

P: R2  R1

Which means “if P = 1, then load the contents of register R1 into

register R2”, i.e., if (P = 1) then (R2  R1)

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 Register Transfer

HARDWARE IMPLEMENTATION OF CONTROLLED TRANSFERS

Implementation of controlled transfer

P: R2 R1

Block diagram Control P Load

R2 Clock
Circuit
n
R1

Timing diagram t t+1

Clock

Load
Transfer occurs here

• The same clock controls the circuits that generate the control function
and the destination register
• Registers are assumed to use positive-edge-triggered flip-flops
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 Register Transfer

SIMULTANEOUS OPERATIONS

● If two or more operations are to occur

simultaneously, they are separated with commas

P: R3  R5, MAR  IR

● Here, if the control function P = 1, load the

contents of R5 into R3, and at the same time
(clock), load the contents of register IR into
register MAR

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 Register Transfer

BASIC SYMBOLS FOR REGISTER TRANSFERS

Symbols Description Examples

Capital letters Denotes a register MAR, R2
& numerals
Parentheses () Denotes a part of a register R2(0-7), R2(L)
Arrow  Denotes transfer of information R2 R1
Colon : Denotes termination of control function P:
Comma , Separates two micro-operations A B, B A

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 Bus and Memory Transfers

MEMORY TRANSFERS
Memory Read
AR
unit Write

DR

Memory read micro-op: DR  M ( DR  M[AR] )

Memory write micro-op: M  DR ( M[AR]  DR )

Summary of Register Transfer Microoperations

A   B Transfer content of reg. B into reg. A
AR  DR(N) Transfer content of N bits portion of reg. DR into reg. AR
A  constant Transfer a binary constant into reg. A
ABUS  R1, Transfer content of R1 into bus A and, at the same time,
R2  ABUS transfer content of bus A into R2
AR Address register
DR Data register
M[AR] Memory word specified by reg. AR
DR  M[AR] Memory read operation: transfers content of
memory word specified by AR into DR
M[AR]  DR Memory write operation: transfers content of
DR into memory word specified by AR
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 Bus and Memory Transfers

BUS AND MEMORY TRANSFER

Bus is a path(of a group of wires) over which information is transferred,
from any of several sources to any of several destinations.
From a register to bus: BUS <- R

Register A Register B Register C Register D

Bus lines

From bus to a register : R <- BUS

Bus lines

Load
Reg. R0 Reg. R1 Reg. R2 Reg. R3

D 0 D1 D 2 D 3
z E (enable)
Select 2x4
w
Decoder
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 Arithmetic Microoperations

ARITHMETIC MICROOPERATIONS

Four types of microoperations

- Register transfer microoperations
- Arithmetic microoperations
- Logic microoperations
- Shift microoperations

* Summary of Arithmetic Micro-Operations

R3  R1 + R2 Contents of R1 plus R2 transferred to R3
R3  R1 - R2 Contents of R1 minus R2 transferred to R3
R2  R2’ Complement the contents of R2
R2  R2’+ 1 2's complement the contents of R2 (negate)
R3  R1 + R2’+ 1 subtraction
R1  R1 + 1 Increment
R1  R1 - 1 Decrement

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Logic Micro-operations

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Register Transfer and Micro-operations 58

Applications of Logic Microoperations

 Logic microoperations can be used to manipulate individual bits or a
portions of a word in a register

 Consider the data in a register A. In another register, B, is bit data that

will be used to modify the contents of A

 Selective-set AA+B
 Selective-complement AAB
 Selective-clear A  A • B’
 Mask (Delete) AA•B
 Clear/Compare AAB
 Insert A  (A • B) + C

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CSE 211
Register Transfer & -operations Logic Microoperations

SELECTIVE SET

● In a selective set operation, the bit pattern in B is

used to set certain bits in A

1100 At
1010 B
1110 At+1 (A  A + B)

● If a bit in B is set to 1, that same position in A gets set

to 1, otherwise that bit in A keeps its previous value

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Register Transfer & -operations Logic Microoperations

SELECTIVE COMPLEMENT

● In a selective complement operation, the bit pattern in B is used

to complement certain bits in A

1100 At
1010 B
0110 At+1 (A  A  B)

● If a bit in B is set to 1, that same position in A gets complemented

from its original value, otherwise it is unchanged

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Register Transfer & -operations Logic Microoperations

SELECTIVE CLEAR

● In a selective clear operation, the bit pattern in B

is used to clear certain bits in A
1100 At
1010 B
0100 At+1 (A  A  B’)

● If a bit in B is set to 1, that same position in A

gets set to 0, otherwise it is unchanged

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Register Transfer & -operations Logic Microoperations

MASK OPERATION

● In a mask operation, the bit pattern in B is used

to clear certain bits in A

1100 At
1010 B
1000 At+1 (A  A  B)

● If a bit in B is set to 0, that same position in A

gets set to 0, otherwise it is unchanged

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Register Transfer & -operations Logic Microoperations

CLEAR OPERATION

● In a clear operation, if the bits in the same

position in A and B are the same, they are cleared
in A, otherwise they are set in A

1100 At
1010 B
0110 At+1 (A  A  B)

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Register Transfer & -operations Logic Microoperations

INSERT OPERATION
● An insert operation is used to introduce a specific bit pattern into A register, leaving the other bit
positions unchanged

● This is done as

– A mask operation to clear the desired bit positions,

followed by
– An OR operation to introduce the new bits into the
desired positions
– Example
● Suppose you wanted to introduce 1010 into the low order
four bits of A: 1101 1000 1011 0001A (Original)
1101 1000 1011 1010 A (Desired)

● 1101 1000 1011 0001 A (Original)

1111 1111 1111 0000 Mask
1101 1000 1011 0000 A (Intermediate)
0000 0000 0000 1010 Added bits
1101 1000 1011 1010 A (Desired)

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Register Transfer and Micro-operations 65

Shift Microoperations
• There are three types of shifts
– Logical shift
– Circular shift
– Arithmetic shift
• What differentiates them is the information that goes into the serial input

• A right shift operation

Serial
input

• A left shift operation

Serial
input

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CSE 211
Register Transfer and Micro-operations 66

Logical Shift
• In a logical shift the serial input to the shift is a 0.

• A right logical shift operation:

0

• A left logical shift operation:

0

• In a Register Transfer Language, the following notation is used

– shl for a logical shift left
– shr for a logical shift right
– Examples:
• R2  shr R2
• R3  shl R3 66

CSE 211
Register Transfer and Micro-operations 67

Circular Shift
• In a circular shift the serial input is the bit that is shifted out of the other
end of the register.

• A right circular shift operation:

• A left circular shift operation:

• In a RTL, the following notation is used

– cil for a circular shift left
– cir for a circular shift right
– Examples:
• R2  cir R2
• R3  cil R3
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CSE 211
Register Transfer and Micro-operations 68

Arithmetic Shift
• An arithmetic shift is meant for signed binary numbers (integer)
• An arithmetic left shift multiplies a signed number by two
• An arithmetic right shift divides a signed number by two
• Sign bit : 0 for positive and 1 for negative
• The main distinction of an arithmetic shift is that it must keep the sign of
the number the same as it performs the multiplication or division

• A right arithmetic shift operation:

sign
bit

• A left arithmetic shift operation: 0

sign
bit

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CSE 211
Register Transfer and Micro-operations 69

Arithmetic Shift
• An left arithmetic shift operation must be checked for the overflow

0
sign
bit

Before the shift, if the leftmost two

V bits differ, the shift will result in an
overflow

• In a RTL, the following notation is used

– ashl for an arithmetic shift left
– ashr for an arithmetic shift right
– Examples:
» R2  ashr R2
» R3  ashl R3

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CSE 211
Register Transfer and Micro-operations 70

Arithmetic Logic and Shift Unit

S3
S2 C
i
S1
S0

D
Arithmetic i

Circuit
Select

0 4x1
C i+1 F
1 i
MUX S3 S2 S1 S0 Cin Operation
2 0 0 0 0 0 F=A
3 0 0 0 0 1 F=A+1
0 0 0 1 0 F=A+B
E 0 0 0 1 1 F=A+B+1
Logic i 0 0 1 0 0 F = A + B’
Bi 0 0 1 0 1 F = A + B’+ 1
Circuit 0 0 1 1 0 F=A-1
A 0 0 1 1 1 F=A
i
0 1 0 0 X F=AB
shr
A 0 1 0 1 X F = A B
i-1 0 1 1 0 X F=AB
shl
A 0 1 1 1 X F = A’
i+1
1 0 X X X F = shr A
1 1 X X X F = shl A 70

CSE 211
 References
!. M. Morris Mano, Computer System Architecture, 3/e,
Pearson education, 2008
References:
1. Carl Hamacher, Zvonko Vranesic, Safwat Zaky, Computer
Organization,5/e, McGraw Hill,2001
2. John P. Hayes, Computer Architecture and Organization,
3/e, McGraw Hill, 1998.
3. William Stallings, Computer Organization and
Architecture, 6/e, Pearson PHI, 2012.

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