computer organization and architecture

Unit - 1
Basic Functional Blocks of a Computer
CPU
Memory
Input-output Subsystems
Control Unit
Unit-1 by M Indraja 1
Computer Organization And Architecture

Basic Computer Model and different units of computer
CPUI/O
Devices
O/p
Devices
Memory

Central Processor Unit (CPU):
In CPU consist of 2 basic blocks
1.Control Unit
2.Execution Unit
 The program control unit has a set of registers and control circuit to generate control signals.
 The execution unit or data processing unit contains a set of registers for storing data and an Arithmatic
and Logic Unit (ALU) for execution of arithmatic and logical operations.

Input Unit:
Keyboard, Mouse, Hard disk, Floppy disk, CD-ROM drive
Output Unit:
Printer, Monitor, Hard disk, Floppy disk.
Memory Unit:
Memory unit is used to store the data and program. CPU can work with the information stored in memory unit.
This memory unit is termed as primary memory or main memory module. These are basically semi conductor
memories.
There ate two types of semiconductor memories -
Volatile Memory: RAM (Random Access Memory).
Non-Volatile Memory: ROM (Read only Memory), PROM (Programmable ROM), EPROM
(Erasable PROM), EEPROM (Electrically Erasable PROM).

Consider the Arithmatic and Logic Unit (ALU) of Central Processing Unit :
Consider an ALU which can perform four arithmatic operations and four logical operations
To distinguish between arithmatic and logical operation, it may use a signal line,
0 - in that signal, represents an arithmatic operation and
1 - in that signal, represents a logical operation.
In the similar manner, it may need another two signal lines to distinguish between four arithmatic
operations.
The different operations and their binary code is as follows:
Arithmatic Logical
000 ADD 100 OR
001 SUB 101 AND
010 MULT 110 NAND
011 DIV 111 ADD

Consider the part of control unit, its task is to generate the appropriate signal at right moment.
There is an instruction decoder in CPU which decodes this information in such a way that computer can
perform the desired task
The simple model for the decoder may be considered that there is three input lines to the decoder and
correspondingly it generates eight output lines. Depending on input combination only one of the output signals
will be generated and it is used to indicate the corresponding operation of ALU.
In our simple model, we use three storage units in CPU,
Two -- for storing the operand and
one -- for storing the results.
These storage units are known as register.

History of Computer:
First Generation (1940-50 :: Vacuum Tube):
ENIAC [1945]: Designed by Mauchly & Echert, built by US army to calculate trajectories for ballistic shells
during World War II. Around 18000 vacuum tubes and 1500 relays were used to build ENIAC, and it was
programmed by manually setting switches
UNIVAC [1950]: the first commercial computer
John Von Neumann architecture: Goldstine and Von Neumann took the idea of ENIAC and developed
concept of storing a program in the memory. Known as the Von Neumann's architecture and has been the basis for virtually
every machine designed since then.
Features:
1.Electron emitting devices
2.Data and programs are stored in a single read-write memory
3.Memory contents are addressable by location, regardless of the content itself
4.Machine language/Assemble language
5.Sequential execution

Second Generation (1950-1964) :: Transistors
William Shockley, John Bardeen, and Walter Brattain invent the transistor that
reduce size of computers and improve reliability. Vacuum tubes have been replaced
by transistors.
First operating Systems:
Handled one program at a time
On-off switches controlled by electronically.
High level languages
Floating point arithmetic.

Third Generation (1964-1974) :: Integrated Circuits (IC)
1.Microprocessor chips combines thousands of transistors, entire circuit on one
computer chip.
2.Semiconductor memory
3.Multiple computer models with different performance characteristics
4.The size of computers has been reduced drastically

Fourth Generation (1974-Present) :: Very Large-Scale Integration (VLSI) /
Ultra Large Scale Integration (ULSI)
1.Combines millions of transistors
2.Single-chip processor and the single-board computer emerged
3.Creation of the Personal Computer (PC)
4.Use of data communications
5.Massively parallel machine

Basics of Architecture and Organization:
Architecture: In architecture the attributes visible to the programmer like instruction set, number of bits used for
data representation, I/O mechanisms, addressing techniques.
Ex: if any instruction like multiplication, addition etc.
Organization: It shows the how features are implemented like control signals, interfaces, memory technology.
Ex: There is a h/w multiply unit or is it done by repeated addition.
In COA there is a families of Architecture.
There are 1. Intel x86 family share the same basic architecture
2.The IBMsystem/370 family share the same basic architecture

Structure of Von Neumann Machine:
The computer system works it basically on stored program principle as introduced by “Scientist Von
Neumann” and it is also called as Von Neumann stored program concept.
1. It is having a storage unit know as main memory (ROM).
2. Main Memory storing programs and data.
3. ALU operating on binary data.(like add, sub, divd etc)
4. CU interpreting instructions from memory and executing,
5. I/O equipment operated by CU,
6. Princeton Institute for Advanced Studies (IAS) in 1952 was designed a architecture called Von Neumann
Architecture.

Computer:
In computer there is two types of components. There are
Function of computer and another one is Structure of computer
Function of Computer:
All computer functions are same in these functions there are 4 categories.
1.Data Processing
2.Data Storing
3.Data Movement
4.Control.

RISC CISC
Acronym It stands for ‘Reduced Instruction Set Computer’.
It stands for ‘Complex Instruction Set
Computer’.
Definition
The RISC processors have a smaller set of instructions with
few addressing modes.
The CISC processors have a larger set of
instructions with many addressing modes.
Memory unit
It has no memory unit and uses a separate hardware to
implement instructions.
It has a memory unit to implement complex
instructions.
Program It has a hard-wired unit of programming. It has a micro-programming unit.
Design It is a complex complier design. It is an easy complier design.
Calculations The calculations are faster and precise. The calculations are slow and precise.
Decoding Decoding of instructions is simple. Decoding of instructions is complex.
Time Execution time is very less. Execution time is very high.
External
memory
It does not require external memory for calculations. It requires external memory for calculations.
Pipelining Pipelining does function correctly. Pipelining does not function correctly.
Code
expansion
Code expansion can be a problem. Code expansion is not a problem.
Disc space The space is saved. The space is wasted.
Applications
Used in high end applications such as video processing,
telecommunications and image processing.
Used in low end applications such as security
systems, home automations, etc.

mPC: Micro Program Counter
mPM : Micro Program Memory
CW: Control Word
IR : Instruction Register
PC: Program Counter

Representation of Real Number:
Binary representation of 41.6875 is 101001.1011
Therefore any real number can be converted to binary number
system
There are two schemes to represent real number :
Fixed-point representation
Floating-point representation

Fixed-point representation:
Binary representation of 41.6875 is 101001.1011
To store this number, we have to store two information,
-- the part before decimal point and
-- the part after decimal point.
This is known as fixed-point representation where the position of decimal point is
fixed and number of bits before and
after decimal point are also predefined.
If we use 16 bits before decimal point and 8 bits after decimal point, in signed
magnitude form, the range is
One bit is required for sign information, so the total size of the number is 25 bits
( 1(sign) + 16(before decimal point) + 8(after decimal point) ).

Floating-point representation:
In this representation, numbers are represented by a mantissa
comprising the significant digits and an exponent part
of Radix R.
The format is:
Numbers are often normalized, such that the decimal point is
placed to the right of the first non zero digit.
For example, the decimal number, 5236 is equivalent to
To store this number in floating point representation, we store
5236 in mantissa part and 3 in exponent part

Thank you

computer organization and architecture

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