UNIT -1 COMPUTER ORGANIZATION (1).pptxxc

COMPUTER
ORGANIZATION
B.TECH III SEM
CSE-4
N SANTOSHI
ASSISTANT PROFESSOR
DEPARTMENT OF ECE

INTRODUCTION
•
Definition of a computer: A computer can be
defined as a fast electronic calculating machine
that accepts the (data) digitized input
information process it as per the list of
internally stored instructions and produces the
resulting information.
•
List of instructions are called programs &
internal storage is called computer memory.

The different types of computers are
 Personal computers
 Note book computers
 Work stations
 Enterprise systems
 Super computers

Functional units
A computer consists of five functionally
independent main parts: input, memory,
arithmetic logic unit (ALU), output and control
unit.

Central processing unit
 CPU is considered as the brain of the
computer.
 CPU has following three components.
◦ ALU(Arithmetic Logic Unit)
◦ Control Unit
◦ Memory or Storage Unit

Arithmetic logic unit (ALU)
 Most of the computer operators are
executed in ALU of the processor like
addition, subtraction, division,
multiplication, comparing etc.
 The operands are brought into the ALU
from memory and stored in high speed
storage elements called register.

Control Unit
 This unit controls the operations of all
parts of the computer but does not carry
out any actual data processing operations.
 This unit controls the operations of all
parts of the computer but does not carry
out any actual data processing operations.

Memory unit
• Its function is to store programs and data.
It is basically of two types
• Primary memory
• Secondary memory
• Primary memory is computer memory that is
accessed directly by the CPU.
• This includes several types of memory, such as the
processor cache and ROM,RAM.

 Memory in which any location can be
reached in a short and fixed amount of time
after specifying its address is called random-
access memory (RAM)
 The time required to access one word is
called memory access time.
 Memory which is only readable by the user
and contents of which can’t be altered is
called read only memory (ROM). It contains
operating system

Secondary memory
 It is used where large amount of data &
programs have to be stored, particularly
information that is accessed infrequently.
 Examples: - Magnetic disks & tapes, optical
disks (ie CD-ROM’s), floppies etc.,

Input units
 Joysticks
 Trackballs
 mouse
 scanners etc are other input devices

Output units
.
•sends the processed results to the outside
world
• Examples:- Printer, speakers, monitor
etc.

INTRODUCTION
 ORGANIZATION AND ARCHITECTURE
◦ Computer Architecture refers to those
attributes of a system that have a direct
impact on the logical execution of a program.
 Examples:
 the instruction set
 the number of bits used to represent various data
types
 I/O mechanisms
 memory addressing techniques
Reference:W. Stallings

 Computer Organization refers to the
operational units and their
interconnections that realize the
architectural specifications.
◦ Examples are things that are transparent to
the programmer:
 control signals
 interfaces between computer and peripherals
 the memory technology being used

Structure and Function
 Structure is the way in which components
relate to each other
 Function is the operation of individual
components as part of the structure

All computer functions are
 Data processing: Computer must be able to
process data which may take a wide variety of
forms and the range of processing.
 Data storage: Computer stores data either
temporarily or permanently.
 Data movement: Computer must be able to
move data between itself and the outside
world.
 Control:There must be a control of the above
three functions.

Processing from storage to i/o

System bus
 Data bus- It defines the bit length of the
processor.eg: 8bit processor have 8 bit data
bus.
 Address bus- It defines the max memory
capacity of the processor.eg:8bit address
means memory capacity=2^8=256 bytes
 Control bus-The physical connections that
carry control information between the
CPU and other devices within the computer

Structure
•Structure is the way in which components
relate to each other.

 Four main structural components:
 Central processing unit (CPU)
 Main memory
 I / O
 System interconnections

 CPU structural components:
 Control unit
 Arithmetic and logic unit (ALU)
 Registers
 CPU interconnections

 Control unit structural components:
 Sequencing logic
 Control unit registers and decoders
 Control memory

Input output subsystems
 I/O subsystems controls all I/O devices.
 The I/O subsystems provide the
mechanism for communication between
the CPU and the outside world(I/O
devices).
 Basic functions include:
◦ Issuing commands to the devices.
◦ Handling interrupts from devices.
◦ Responding errors from devices.

Computer Components
 The Control Unit (CU) and the Arithmetic
and Logic Unit (ALU) constitute the
Central Processing Unit (CPU)
 Data and instructions need to get into the
system and results need to get out
◦ Input/output (I/O module)
 Temporary storage of code and results is
needed
◦ Main memory (RAM)

What is a Register?
 A register is a very small amount of very fast memory
that is built into the CPU (central processing unit).
 Contents can be accessed at extremely high speeds.
 Registers are used to store data temporarily during
the execution of a program.
 Different processors have different register sizes.
 Registers are normally measured by the number of bits
they can hold, for example, an 8-bit register means it
can store 8 bits of data or a 32-bit register means it
can store 32 bit of data

List of Registers for the Basic Computer
Reference: morris mano

Basic computer registers and memory

Computer registers
 ACCUMULATOR (AC):The processor register
AC consists of 16-bits. It is used to hold the
results or partial results of arithmetic and
logical operations.An accumulator is a register
in which intermediate arithmetic and logic
results are stored.
 DATA REGISTER (DR):The register DR
consists of 16-bits and it is used to hold
memory operands (data).This register contains
the data to be written into memory or receives
the data read from memory.

Computer registers
 TEMPORARY REGISTER (TR):Temporary
register have 16-bits and it provides temporary
storage of variables or results.
 INSTRUCTION REGISTER (IR):The instruction
register consists of 16-bits.The purpose of the
instruction register is to hold a copy of the
instruction which the processor is to execute. In
our basic computer, instruction register (IR) holds
instruction code which is read from memory.

Computer registers
 ADDRESS REGISTER (AR):This register specifies
the address in memory for next read or writes
operations.The address register consists of 12-bits.
 PROGRAM COUNTER (PC): Program counter has
12-bits and it holds the address of the next
instruction to be read from memory after the
current execution is executed.The instructions are
read sequentially because the program counter
automatically increments after fetching the current
instruction.

Computer registers
 INPUT REGISTER (INPR): Input register
has 8-bits. INPR register receives a
character from an input device and
delivers it to the AC.
 OUTPUT REGISTER (OUTR): Output
register has 8-bits.The output register
receives information from AC and
transfer it to the output device.

example
 ADD AC,DR
◦ AC=AC+DR
◦ This instruction adds the contents of AC and
DR stores the result in Accumulator.
AC=1234H
DR=2222H
After execution AC=3456H

Instruction
 A Computer Instruction is a binary code
thatThat specify a sequence of micro-
operations for the computer.
 Micro-operations are detailed low-level
instructions used in some designs to
implement complex machine instructions.

Instruction Set
 An Instruction set is a group of bits that
instruct computer to perform a specific
operation.
 The basic computer has three
instructions code formats, each of 16 bit.

Types of Instructions
 These are of three types:
◦ Memory-Reference instruction
◦ Register-Reference instruction
◦ Input-Output instruction

Memory-Reference instruction
 An instruction that has one or more of its
operand addresses referring to a location
in memory, as opposed to one of the
CPU registers or some other way of
specifying an operand.

Register-Reference instruction
 A register-reference instruction specifies
an operation on or a test of the AC
register.
 An operand from memory is not needed;
therefore, the other 12 bits are used to
specify the operation or test to be
executed.

Input-Output instruction
 An input-output instruction does not
need a reference to memory and is
recognized by the operation code Ill with
a 1 in the leftmost bit of the instruction.
 The remaining 12 bits are used to specify
the type of input-output operation or test
performed.

Various Instructions format
Reference: Morris mano

Instruction Cycle
 The time period during which one
instruction is fetched from memory and
execute when a computer gives an
instruction in machine language.
 Each instruction cycle in turn is subdivided
into a sequence of subcycles or phases.
 After the execution the program counter
is incremented to point to the next
instruction.

Phases of Instruction Cycle
1. Fetch the instruction
2. Decode the instruction
3. Read the effective address from memory
if the instruction has an indirect address.
4. Execute the instruction

The program counter PC is loaded with the address of the first
instruction in the program
The sequence counter SC is cleared to 0, providing a decoded timing signal To.
After each clock pulse, SC is incremented by one, so that the timing signals
go through a sequence T0,T1,T2, and so on.
The micro operations for the fetch and decode phases can be specified by
the following register transfer statements.

Register Transfer for Fetch phase

 AR is connected to the address inputs of
memory, it is necessary to transfer the
address from PC to AR during the clock
transition associated with timing signal T0
 The instruction read from memory is
then placed in the instruction register IR
with the clock transition associated with
timing signal T1•

 At the same time, PC is incremented by one
to prepare it for the address of the next
instruction in the program.
 At time T2, the operation code in IR is
decoded, the indirect bit is transferred to
flip-flop I, and the address part of the
instruction is transferred to AR .
 Note: SC is incremented after each clock
pulse to produce the sequence To,T1, and T2•

To implement the first register transfer
statement
To provide the data path for the transfer of
PC to AR we must apply timing signal T0 to
achieve the following connection:
1. Place the content of PC onto the bus by
making the bus selection inputs S2S1S0 equal to
010.
2. Transfer the content of the bus to AR by
enabling the LD input of AR .

To implement the second register
transfer statement
 It is necessary to use timing signal T1 to provide
the following connections in the bus system.
1. Enable the read input of memory.
2. Place the content of memory onto the bus by
making S2S1S0 = Ill.
3. Transfer the content o f the bus t o IR b y enabling
the LD input of IR .
4. Increment PC by enabling the INR input of PC .

Determining type of instruction
 The timing signal that is active after the
decoding is T3.
 During time T3 the control unit determines
the type of instruction that was just read
from memory.
 Decoder output D, is equal to 1 if the
operation code is equal to binary Ill.
 we determine that if D7 = I, the instruction
must be a register-reference or input-output
type.

 If D, = 0, the operation code must be one
of the other seven values 000 through
110, specifying a memory-reference
instruction.
 If D7 = 0 and I = 1, we have a
memoryreference instruction with an
indirect address.

Flow Chart For Instruction Cycle

Definition of Register Reference
Instructions
 Register Reference Instructions are those
which refer registers instead of some
memory address or memory location for
data to operate on

Register reference instructions
Reference: Morris mano

 There are a total 12 register reference
instructions in computer architecture that
are in use and they are 1. CLA, 2. CMA, 3.
CIL, 4. CIR, 5. INC, 6. SPA, 7. SNA, 8. SZA,
9. CLE, 10. CME, 11. SZE, 12. HLT
 Each instruction has its own functionality
and all these register reference
instructions operate on accumulator only

Memory reference instructions
There are seven different memory-reference
instructions.

AND to AC
This is an instruction that performs the
AND logic operation on pairs of bits in
AC and the memory word specified by
the effective address.The result of the
operation is transferred to AC .The
microoperations that execute this
instruction are:

Flow chart for memory reference
instructions

Addressing modes
 The operation field of an instruction
specifies the operation to be performed.
 This operation must be executed on
some data stored in computer registers
or memory words.
 The way the operands are chosen during
program execution is dependent on the
addressing mode of the instruction.

Types of addressing modes
 Implied Mode
 Immediate Mode
 Register Mode
 Register Indirect Mode
 Autoincrement or Autodecrement Mode
 Direct Address Mode
 Indirect Address Mode
 Relative Address Mode
 Indexed Addressing Mode
 Base Register Addressing Mode

Implied addressing mode
 In this mode the operands are specified
implicitly in the definition of the
instruction.
 Example: CMA,CLA,CLE
 all register reference instructions that use
an accumulator are implied-mode
instructions.

Immediate Mode
 In this mode the operand is specified in
the instruction itself. In other words, an
immediate-mode instruction has an
operand field rather than an address field.
 Immediate- mode instructions are useful
for initializing registers to a constant value.
 Eg:ADD A,1234H
 A=2222H
 AFTER EXECUTION A=3456H

Register Mode
 In this mode the operands are in registers
that reside within the CPU.The particular
register is selected from a register field in
the instruction.
 Eg:Add A,DR

Register Indirect Mode
 In this mode the instruction specifies a register in the
CPU whose contents give the address of the operand in
memory. In other words, the selected register contains
the address of the operand rather than the operand itself.
 The advantage of a register indirect mode instruction is
that the address field of the instruction uses fewer bits to
select a register than would have been required to specify
a memory address directly.
 Eg:ADD A,[AR]
 AR=5000H
 5000H=1234H
 ADD A,[5000H]

Autoincrement or Autodecrement Mode
 This is similar to the register indirect
mode except that the register is
incremented or decremented after (or
before) its value is used to access
memory.
 MOV A,[AR]
 INC AR
 LOOP

Direct Address Mode
 In this mode the effective address is equal
to the address part of the instruction.The
operand resides in memory and its
address is given directly by the address
field of the instruction.
 In a branch-type instruction the address
field specifies the actual branch address.
 Eg:ADD A ,[5000H]
 Eg : BUN 2000H

Indirect Address Mode:
 In this mode the address field of the
instruction gives the address where the
effective address is stored in memory.
Control fetches the instruction from
memory and uses its address part to
access memory again to read the effective
address.

Relative Address Mode
 In this mode the content of the program counter
is added to the address part of the instruction in
order to obtain the effective address.
 The address part of the instruction is usually a
signed number (in 2' s complement
representation) which can be either positive or
negative.
 When this number is added to the content of
the program counter, the result produces an
effective address whose position in memory is
relative to the address of the next instruction.

Indexed Addressing Mode
 In this mode the content of an index
register is added to the address part of
the instruction to obtain the effective
address.
 The index register is a special CPU
register that contains an index value.
 The address field of the instruction
defines the beginning address of a data
array in memory.

Base Register Addressing Mode
 In this mode the content of a base register is added
to the address part of the instruction to obtain the
effective address.
 This is similar to the indexed addressing mode except
that the register is now called a base register instead
of an index register.
 An index register is assumed to hold an index number
that is relative to the address part of the instruction.
 A base register is assumed to hold a base address and
the address field of the instruction gives a
displacement relative to this base address.

Numeric example for Addressing modes

INSTRUCTION SET
 computer instructions can be classified
into three categories:
1. Data transfer instructions
2. Data manipulation instructions
3. Program control instructions

Data transfer instructions
 Data transfer instructions cause transfer
of data from one location to another
without changing the binary information
content.
 Data manipulation instructions are those
that perform arithmetic, logic, and shift
operations.

Data transfer instructions
Mov AC,R1

ADDRESSING MODES FOR LOAD
INSTRUCTION

Data Manipulation Instructions
 Data manipulation instructions perform
operations on data and provide the
computational capabilities for the computer.
 The data manipulation instructions in a
typical computer are usually divided into
three basic types:
1. Arithmetic instructions
2. Logical and bit manipulation instructions
3. Shift instructions

Logical and Bit Manipulation Instructions

Program Control
 Program control instructions provide
decision-making capabilities and change
the path taken by the program when
executed in the computer.
 The instruction set of a particular
computer determines the register
transfer operations and control decisions
that are available to the user.

UNIT -1 COMPUTER ORGANIZATION (1).pptxxc

More Related Content

Similar to UNIT -1 COMPUTER ORGANIZATION (1).pptxxc (20)

Recently uploaded (20)

UNIT -1 COMPUTER ORGANIZATION (1).pptxxc