UNIT-1

Dr. S. K. Verma
Introduction
● Computer Organization vs Computer Architecture
● System And Computer System
● Computer Types
● Embedded computers
●used for a specific purpose
● Personal computers
●Desktop computers
●Workstation computers
●Portable and Notebook computers
● Servers and Enterprise systems
● Supercomputers and Grid computers
● cloud computing
Eight Great Ideas in Computer
Architecture
● Design for Moore’s Law
● Use Abstraction to Simplify Design
● abstractions to represent the design at different levels of
representation;
● Make the Common Case Fast
● Performance via Parallelism
● Performance via Pipelining
● Performance via Prediction
● Hierarchy of Memories
● Dependability via Redundancy
Functional Units
Contd.
● Instructions, or machine instructions, are explicit
commands
● transfer of information within a computer or between the
computer and its I/O devices
● arithmetic and logic operations to be performed
● program is a list of instructions which performs a task
.
● Data are numbers and characters used as operands
by the instructions.
● Each instruction, number, or character is encoded as
a string of binary digits called bits
Input Units
● Computers accept coded information through
input units
● Keyboard touchpad, mouse, joystick, and
trackball.
● Microphones
● Cameras
● Digital communication facilities
Memory Unit
● There are two classes of storage:
● Primary Memory
● main memory
● a fast memory that operates at electronic speeds
● memory consists of a large number of semiconductor storage cells
● cells are rarely read or written individually
● handled in groups of fixed size called words
● one word can be stored or retrieved in one basic operation
● word length of the computer
● distinct address is associated with each word location
● A 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).
● memory access time
Contd.
● Cache Memory
● adjunct to the main memory, a smaller, faster RAM unit,
called a cache.
● Used to hold sections of a program that are currently being
executed.
● cache is tightly coupled with the processor and is usually
contained on the same integrated-circuit chip.
● Secondary Storage
● additional, less expensive, permanent secondary storage is
used.
● Access times for secondary storage are longer than for
primary memory
● magnetic disks, optical disks (DVD and CD), and flash
memory devices.
Arithmetic and Logic Unit
● operations are executed in the arithmetic and
logic unit (ALU)
● When operands are brought into the processor
they are stored in high-speed storage elements
called registers.
● register can store one word of data
● Access times to registers are even shorter than
access times to the cache unit
Output Unit
● output unit is the counterpart of the input unit.
● function is to send processed results to the
outside world.
Control Unit
● Coordination among different units done by CU.
● Control circuits are responsible for generating the timing
signals.
● large set of control lines (wires) carries the signals used for
timing and synchronization of events in all units.
● 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.
Basic Operational Concepts
● Load R2, LOC
● Add R4, R2, R3
● Store R4, LOC
Contd.
Contd.
Contd.
Contd.
● the processor contains a number of registers
used for several different purposes.
● instruction register (IR) holds the instruction
that is currently being executed.
● program counter (PC) is another specialized
register
● PC points to the next instruction that is to be
fetched from the memory.
● general-purpose registers R0 through Rn−1,
often called processor registers
Contd.
● typical operating steps:
● A program must be in the main memory in order for it to be
executed.
● Execution of the program begins when the PC is set to point
to the first instruction of the program.
● contents of the PC are transferred to the memory along
with a Read control signal.
● the addressed word has been fetched from the memory
and loaded into register IR.
● the contents of the PC are incremented so that the PC
points to the next instruction to be executed
● Normal execution of a program may be preempted if some
device requires urgent service.
Contd.

●processing required for a single instruction is called an instruction

cycle.
●fetched instruction is loaded into a register in the processor known
as the instruction register (IR).
●instruction contains bits that specify the action the processor is to
take.
●Actions category:
●Processor-memory
●Processor-I/O
●Data processing
●Control
Contd.
Instruction Set Architecture
Memory Locations and Addresses
● a group of n bits can be
stored or retrieved in a
single, basic operation.
● n bits is called the word
length
Contd.
● Byte Addressability
● byte-addressable memory is used
● if the word length of the machine is 32 bits,
successive words are located at addresses 0, 4,
8, . . . , with each word consisting of four bytes.
● Big-Endian and Little-Endian Assignments
Contd.
Representing Instructions in the
Computer
● layout of the instruction is called the instruction
format
● the numeric version of instructions machine
language and a sequence of such instructions
machine code.

● op: Basic operation of the instruction, traditionally called the opcode.

● rs: The first register source operand.
● rt: The second register source operand
● rd: The register destination operand. It gets the result of the operation.
● shamt: Shift amount.
● funct: Function. This field, often called the function code, selects the specific variant of the
operation in the op field.
MIPS (Microprocessor without Interlocked Pipelined Stages)
Instructions and Instruction
Sequencing
● computer must have instructions capable of
performing four types of operations:
● Data transfers between the memory and the processor
registers
● Arithmetic and logic operations on data
● Program sequencing and control
● I/O transfers
Contd.
● Register Transfer Notation
● the contents of any location are denoted by placing
square brackets around its name
●R2 [LOC]
●R4 [R2] + [R3]
● the right hand side of an RTN expression always
denotes a value
● left-hand side is the name of a location.
Contd.
● Assembly-Language Notation
● the transfer from memory location LOC to processor
register R2, is specified by
●Load R2, LOC
●Add R4, R2, R3
● RISC and CISC Instruction Sets
Contd.
Addressing Modes
● Immediate
● Direct
● Indirect
● Register
● Register indirect
● Displacement
● Stack
A = contents of an address field in the instruction
R = contents of an address field in the instruction that refers
to a register
EA = actual (effective) address of the location containing the
referenced operand
(X) = contents of memory location X or register X
Contd.
● Virtually all computer architectures provide more
than one of addressing modes. (mode field)
● the effective address will be either a main memory
address or a register.
● Immediate Addressing
● the operand value is present in the instruction
●Operand = A
● advantage of immediate addressing is that no memory
reference other than the instruction fetch is required to
obtain the operand
● disadvantage is that the size of the number is restricted to
the size of the address field
Contd.
● Direct Addressing
● the address field contains the effective address of the operand:
● EA = A
● It requires only one memory reference and no special
calculation.
● limitation is that it provides only a limited address space.
● Indirect Addressing
● the address field refer to the address of a word in memory
● EA = (A)
● advantage of approach is that for a word length of N, an
N
address space of 2 is now available.
● disadvantage is that three or more memory references could
be required to fetch an operand.
Contd.
● Register Addressing
● It is similar to direct addressing
● address field refers to a register rather than a main memory
address:
●EA = R
● if the contents of a register address field in an instruction is
5, then register R5 is the intended address, and the operand
value is contained in R5.
● advantages of register addressing are
●a small address field is needed in the instruction
●no time- consuming memory references are required
● modern processors employ multiple general-purpose
registers, placing a burden for efficient execution on the
assembly- language programmer
Contd.
● Register Indirect Addressing
● register indirect addressing is analogous to indirect
addressing.
●EA = (R)
● advantages and limitations of register indirect
addressing are the same as for indirect addressing.
● register indirect addressing uses one less memory
reference than indirect addressing.
● Displacement Addressing
● combines the capabilities of direct addressing and register
indirect addressing
●EA = A + (R)
Contd.
● Relative addressing
● Base-register addressing
● Indexing
● relative addressing
● also called PC-relative addressing
● implicitly referenced register is the program counter (PC)
● Relative addressing exploits the concept of locality
● If most memory references are relatively near to the
instruction being executed, then the use of relative
addressing saves address bits in the instruction.
Contd.
● base-register addressing
● The referenced register contains a main memory address,
and the address field contains a displacement
● Indexing
● The address field references a main memory address, and
the referenced register contains a positive displacement
from that address
● use of indexing is to provide an efficient mechanism for
performing iterative operations.
● A, A + 1, A + 2, . . . ,
● The value A is stored in the instruction’s address field, and
the chosen register, called an index register, is initialized to
0. After each operation, the index register is incremented
by 1.
Contd.
● Stack Addressing
● a stack is a linear array of locations
● Also known as pushdown list or last-in-first-out
queue
Number Representation and
Arithmetic Operations
● Integers
● B = bn−1 . . . B1b0
●where b= 0 or 1 for 0 ≤ i ≤ n − 1. This vector can represent
an unsigned integer value V(B) in the range 0 to 2− 1.
n

n−1 1 0
●V(B) = bn−1 × 2 + +b1 × 2 + b0 × 2
● Three systems are used for representing
numbers:
● Sign-and-magnitude
● 1’s-complement
● 2’s-complement
Contd.
● The rules for addition and subtraction of n-bit signed
numbers using the 2’scomplement representation
● To add two numbers, add their n-bit representations, ignoring
the carry-out bit from the most significant bit (MSB) position.
The sum will be the algebraically correct value in 2’s-
complement representation if the actual result is in the
n n−1
range−2 −1 through+2 − 1.
● To subtract two numbers X and Y , that is, to perform X −
Y , form the 2’s-complement of Y , then add it to X using the
add rule. Again, the result will be the algebraically correct
value in 2’s-complement representation if the actual result
n n−1
is in the range −2 −1 through+2 − 1
Contd.
● Sign Extension
● Overflow in Integer Arithmetic
● When the actual result of an arithmetic operation is
outside the representable range, an arithmetic overflow
has occurred.
● an overflow has occurred when the sign of the sum
is not the same as the signs of the summands.
Contd.
● Floating-Point Numbers
● binary floating-point number can be represented by:
●a sign for the number
●some significant bits
●a signed scale factor exponent for an implied base of 2
● IEEE (Institute of Electrical and Electronics
Engineers) standard for 32-bit floating-point number
representation uses
● a sign bit
● 23 significant bits
● 8 bits for a signed exponent of the scale factor
Contd.
● Character Representation
● characters is ASCII (American Standard Code for
Information Interchange).
Adders
● Half Adder
Contd
● Full Adder
Contd.
● Four Bit Adder
Contd.
● Carry Look Ahead Adder
Contd.
● Binary Adder and Subtractor
Hardware for Addition and Subtraction
Multiplication
● unsigned integers
● Multiplication involves the generation of partial products, one
for each digit in the multiplier. These partial products are then
summed to produce the final product.
● When the multiplier bit is 0, the partial product is 0. When
the multiplier is 1, the partial product is the multiplicand.
● each successive partial product is shifted one position to
the left relative to the preceding partial product.
● The multiplication of two n-bit binary integers results in a
product of up to 2n bits in length
Contd.
Flowchart for unsigned Binary
Multiplication
Contd.
● twos complement
multiplication
● multiplication of a binary
n
number by 2 is accomplished
by shifting that number to the
left n bits.
● the partial products should be
viewed as 2n-bit numbers
generated from the n-bit
multiplicand.
Contd.
● Booth’s algorithm
Contd.
Division
●
Contd.
Contd.
● D=Q*V+R

● Carry Save Multiplier

Floating-Point Representation

●
Floating-Point Arithmetic
● A floating-point operation may produce one of these
conditions:
● Exponent overflow: A positive exponent exceeds the
maximum possible exponent value.
● Exponent underflow: A negative exponent is less than the
minimum possible exponent value (e.g., - 200 is less than
-127).
● Significand underflow: In the process of aligning
significands, digits may flow off the right end of the
significand.
● Significand overflow: The addition of two significands of
the same sign may result in a carry out of the most
significant bit.
Addition and Subtraction
● There are four basic phases of the algorithm for
addition and subtraction:
● Check for zeros.
● Align the significands.
● Add or subtract the significands.
● Normalize the result.
Multiplication and Division
Contd.
Thank You (End Unit 1)