General Aspects of Computer Organization(Lecture-1)

R S Ananda Murthy

Associate ProfessorDepartment of Electrical & Electronics Engineering,

Sri Jayachamarajendra College of Engineering,Mysore 570 006

R S Ananda Murthy General Aspects of Computer Organization

Specific Learning Outcomes

After completing this lecture the student should be able to –List the four main blocks in a digital computer.Explain the meaning of address bus, data bus and controlbus in a digital computer.List the differences between a microprocessor and amicrocontroller.Explain the meaning of bit, nibble, byte and word length ofa microcontroller or a microprocessor.Explain how the word length of a processor affects itsperformance.Explain the meaning of address space.Explain the Stored Program Concept of Von Neuman.

R S Ananda Murthy General Aspects of Computer Organization

Functional Units in a Digital Computer

CPUInput Output

Memory

ExternalWorld

ExternalWorld

Arrows indicate direction of information flow.Central Processing Unit (CPU) executes the programstored in memory.Typical devices in input block: keyboard, mouse.Typical devices in output block: monitor, speaker, printer.

R S Ananda Murthy General Aspects of Computer Organization

Address, Data and Control Buses in Computer

Memory

CPU

Input

Output

Address Bus

Data Bus

Control Bus

RealWorld

A set of parallel wires is called a bus.Address is output by the CPU on the address bus.Data is transmitted between the CPU and other devicesover the data bus.Control signals are transmitted over the control bus.

R S Ananda Murthy General Aspects of Computer Organization

Microprocessor – CPU on a Chip

Arithmetic LogicUnit (ALU)

Register ArrayControlUnit (CU)

Central Processing Unit (CPU)

CU generates signals required to fetch instructions fromthe memory and execute them.ALU performs arithmetic and logical operations.Register array has registers to store data temporarily.Microprocessor is a CPU on a single chip.

R S Ananda Murthy General Aspects of Computer Organization

Microcontroller – CPU and Peripherals on a Chip

CPU R/WM ROM

I/OPorts

Timer/Counter

SerialCOMPort

Microcontroller

Some modern microcontrollers even have on-chipAnalog-to-Digital Converter (ADC) and Digital-to-AnalogConverter (DAC).

R S Ananda Murthy General Aspects of Computer Organization

Bit, Nibble, Byte and Word Length of CPU

A binary digit is known as bit. It can be 0 or 1.In modern digital computers all instructions and data arerepresented using bits.A group of four bits is a nibble. Eg. 1101, 1010.A group of eight bits is a byte. Eg. 11011010, 10101010.The data bus width is known as word length of CPU. Foreg. ATmega328 MCU has a word length of 1-byte becauseits data bus width is 8-bits.A CPU with longer word length is faster because it canprocess more bits in one operation.

R S Ananda Murthy General Aspects of Computer Organization

No. of Bits in Address and Address Space

MemoryAdr. Hex

0000H

FFFFH

0001HStarting

Ending

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65536 Locations

0000 0000 0000 0000B

Address in Binary

1111 1111 1111 1111B

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0000 0000 0000 0001B

With N bits in the address, CPU can access 2N locations.Eg. if there are 16-bits in the address as shown above,then, the address space has 216 = 65536 locations.

R S Ananda Murthy General Aspects of Computer Organization

Von Neumann’s Stored Program Concept

Address Memory

0000 Byte0001 Byte0002 Byte0003 Byte

0020

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CPU

0002PC

Halt

Content ofa memorylocation

0021

Program Counter (PC) – also known as Location Counter –in side the CPU points to the next instruction in thememory to be fetched and executed.PC stops incrementing when HALT instruction isrecognized by the CPU.

R S Ananda Murthy General Aspects of Computer Organization

License

This work is licensed under aCreative Commons Attribution 4.0 International License.

R S Ananda Murthy General Aspects of Computer Organization