Complete Computer Knowledge Portal

Monday, May 27, 2013

Conductors, Semiconductors, Insulators

Solids can be classified on the basis of electrical conductivity as:
1) Conductors
2) Semiconductors
3) Insulators

Conductors: The Substances which easily allow electric current pass through them are called conductors. E.g. Copper, Aluminium has large no. of free electrons.

Conductors contain no forbidden energy gap between valance band and conduction band. They overlap each other as shown in the given image. Without supplying any additional energy valance electrons become free electrons which make metals like Copper, Aluminium good conductors of electricity.


The electronic components that are used to store the charge are called Capacitors. This capability of capacitors to store the energy (Charge) is called capacitance. Capacitance is measured in Farads (F). Farad is a very high unit of capacitance. Lower units are Micro Farad (µF) and Pico Farad (pF).

Capacitor consists of two conducting plates that are separated by an insulating material which is known as dielectric. Capacitor offers very low impedance to AC but it blocks DC. The reason behind this is that
XC =1/2πfc and for AC frequency is 50-60 Hz but for DC frequency is 0 hence XC= Infinite.

Sunday, May 26, 2013

Resistors and Their Types

The components which resist or oppose the flow of electrons in any electrical or electrical circuit is called resistor. The force by which it resists flow of current is called resistance. It is measured in Ohms (Ω). Resistors are used to limit current flowing through a circuit or to divide the voltage in a circuit.

Types of Resistors
i) Fixed Value Resistors.
ii) Variable Value Resistors.

Wednesday, May 22, 2013


It is a set of program instructions that are designed to perform a specific task and are written separately and stored in memory.Subroutines can be defined within programs, or separately in libraries that can be used by multiple programs.
It is totally different from functions in the manner that function takes parameters, perform works and does not alter any value or work with any value outside it's scope .Functions also returns some value ,although their are some function in C that do not return any value like Void() . Subroutine directly work with the values of the caller/the code segment which invoked it, and does not return values.

Monday, May 20, 2013

Features of 8086 Microprocessor

1) It is 16 bit N- Channel HMOS (High Speed MOS) processor. Its CMOS version 80C86 is also available.
2) Intel 8086 Draws 360 mA on 5V whereas 80C86 draws 10 mA at 5 V.
3) It can operate at standard temperature Range 32˚ F to 180˚ F and at extended temperature range 40˚F to +225˚F.

Instruction Cycle

Before knowing instruction set we have to know two things i.e. opcode and operand. Operand is the data on which operation is to be performed and opcode is the operation which has to be performed. Thus the time taken to fetch the opcode from the memory and execute the operation on operand is a complete Instruction Cycle. Instruction cycles consist of fetch cycle and execute cycle.

IC (Instruction Cycle) = FC (Fetch Cycle) + EC (Execute Cycle)

Instruction set of 8085

Instruction set is a collection of instructions that a processor can execute. Microprocessor operates on these instructions. If an instruction that is not in the instruction set of a particular microprocessor, is invalid for that processor. Each instruction in 8085 belongs to a particular group depending upon the task they perform. These Instructions are classified as:

1) Data Transfer Group: These Instructions are used to transfer data from one register to another, memory to register or from register to memory. E.g. MOV, MVI, STA, LXI, LDA, LHLD, SHLD, LDAX, STAX, XCHG etc.

Thursday, May 16, 2013

Intel 8085 Block Diagram

Intel 8085 consists of following three main sections:

Arithmetic and Logical Unit:- The main function of ALU is to perform arithmetic and logical operations such as Addition, subtraction, Logical AND, Logical OR, Complement, Increment, Decrement, Shift Operations etc.

Timing and Control Unit: - Generation of timing and control signals for the execution of instructions is done by this unit. It controls and monitors flow of data between CPU and I/O devices. It works as brain for Computer System.X1, X2, Clock Out, ready, ALE, HOLD, HLDA are some examples of signals generated by this unit.

Tuesday, May 14, 2013

Features of 8085 Microprocessor

Intel 8085 is an 8 bit Microprocessor developed by Intel in 1977.main Features of this Processor are as follows:
1) It is 8 bit, NMOS Microprocessor.
2) It has 16 Address Lines and 8 bit data bus is multiplexed with lower part of 8 bit address lines to limit no. of pins to 40.
3) It operates at Single +5 V DC Supply.
4) It consist of following Register sets:

Monday, May 13, 2013

Difference Between Hardwired Control and Micro Programmed Control

Timing and control signals are generated by two methods.i.e. Hardwired control and Micro Programmed control.Below given table illustrates the difference between both of them.

Sr. No.
Hardwired Control
Micro programmed Control
It is Implemented with the help of gates, Flip Flops, Decoders and other digital circuits.
This is Implemented by Programming control memory to perform required sequence of Micro operations.
If changes are required to be made, we have to change the entire hardware or hardware connections.
Changes can be done by just updating the micro program in control memory.
Update or changes are much expensive.
Changes can be done at low or no cost.
Difficult to Implement.
Easy to Implement.

Half Adder, Full Adder

Half Adder

The Combinational circuit that performs arithmetic addition of two binary digits is called half adder. Variables that are supplied to input of half adder are called augend and addend. The Output obtained is sum and carry. Figure given below shows logical and symbolic representation of  half adder.

Here A and B are two inputs and S, C are sum and Carry respectively.Half Adder is the combination of one XOR gate and one AND gate.
S= A'B +AB'

Difference between POP and OOP

Acronym for
Procedure Oriented Programming
Object Oriented Programming
Program Division
Program is divided into small parts that are called functions.
Program is divided into small parts that are called objects.
Importance is given to functions and sequence of actions rather than data.
Importance is given to Data rather than procedures or objects.
Approach Type
It is a top down approach.
It is bottom up approach.
Access Specifier
It does not have access specifiers.
It has access specifiers named as: Public, Private and Protected.

Common Errors in Programming Languages

Following are the Most Common Errors in Programming Languages:

1) Syntax Errors: These are those types of errors that arise when a statement is not written as per the defined rules. This is the violation of rules. These types of errors are generated by the compiler. This may include:
a) Improper Termination of Statement.
b) Undeclared Variable use.
c) Missing Quotes
d) Missing Braces.

Wednesday, May 8, 2013

Ubuntu Installation Step by Step

Boot Your System with Ubuntu 12.10 Installation CD/DVD.

Database Management System (DBMS) Interfaces

DBA Interface: This interface is used by the database administrator to create databases, Users, to set system parameters for changing database schema etc. Fig. given below shows admin menu where DBA is can create new user and can assign privileges to him.

Tuesday, May 7, 2013

Classification of Database Management System

Database Management System can be classified on several DBMS criteria.

A) On the Basis of Data Models.

Data model is a collection of high level data description that hides many low level storage details. A data Model has following three Components:
1) A Structural Part that consist of a set of rules according to which database is constructed.
2) A Manipulating Part That defines type of operations that are allowed on data.
3) A set of integrity rules that ensures that data is correct.
The Data Models are further divided into Three Categories: 

Windows XP Virtual Installation

Many times it becomes necessary to install lower version of windows because some applications still does not work with higher version of windows.This Problem can be resolved by either making your system dual bootable, means two operating systems on same hard disk.But the Problem with this technique is that at the same time you can use only one operating system.

Another approach is to install Operating System Virtually.This installation provide installation of multiple Operating Systems Virtually and each can work as stand alone system.The Main advantage of using this technique is that you can access the multiple OS on the same time. Another advantage is that if you have only single PC and you want to test any client server based model you can use this.e.g. you can install Windows Server 2012 virtually on windows 7 and can create a domain where your system can work as client and virtual server will work as domain controller.

Monday, May 6, 2013

Index Allocation

It is the Disk allocation technique in which each file has its own index block which is an array of disk block addresses. The nth entry in the index block points to nth block of file.
Whenever a file is created its index block is initialized, free block is taken from the disk and its entry is made into index table. whenever  file uses a new block its entry is made into index table. Index table consist of the addresses of all disk blocks on which a particular file is written.

Sunday, May 5, 2013

Linked Allocation

It is a disk allocation technique in which files are stored in a linked fashion and scattered way. Directory entry is used that contains pointer to first disk block of file and each block contains pointer to next block.

These Pointers are not made visible to users. Each block has 512 bytes in size out of which 4 bytes are used to store pointer and rest 508 bytes is used by the user.

This Technique has the advantage that there is no external fragmentation and files can be stored anywhere. Another advantage is that there is no need to define the size of file and it can grow as long as free blocks are available.

Saturday, May 4, 2013

Setup Windows 7 from USB drive

Here are Some Simple steps that are used to make USB pen drive bootable that can be used to install windows 7 on your PC.
1) First Step is to download Power ISO Software from Official site of Power ISO(Click here to download)

2) Install Power ISO and open it (Please choose all file extension support while installation).

3) Open Power ISO it will give Thank You message click on continue unregistered version. This will also create bootable USB .(Purchase License is Optional)

First Fit, Best Fit and Worst Fit Memory Allocation

Best fit Allocation: It is the Contiguous allocation technique in which file is saved on the blocks whose size is same to file size or little more than file size. E.g. if we want to save a 200 Kb file and one block of 250KB is available then it will be saved to this available block.

The advantage of using this technique is best disk utilization but has the disadvantage that it is slow. Every time we want to save a file, we have to find a space whose size is either similar to file size or is slightly more.

Another Problem Associated with this technique is that if we want to extend the file contents than it can’t be implemented.

Contiguous Allocation

It is the Memory allocation technique in which contiguous blocks of this are used to save files. Whenever a file is created its size is calculated and based upon its size contiguous blocks are allocated to it for store. This allocation can be Best Fit, Worst Fit or First Fit.

The Main Advantage of using this technique is that it provides fast file access since whole file is allocated contagious blocks.

Directory Implementation

Directory efficiency, performance and reliability are totally dependent on the technique used to store them. They are saved on Disks with two well Known Techniques:

1) Linear List: It is the Simple method of directory implementation. It makes use of a file name and a pointer to data blocks. Whenever a new file is created, whole directory is checked to make sure that no existing file has the same name. If the directory contains no file with this name it is added to the end of directory. For the deletion operation file is searched and the allocated space is released.

The Main Disadvantage is of this technique is that every time we create a new file, directory has to be checked for existing file name .The second problem is that files are accessed in a serial fashion which results in slow performance 

Friday, May 3, 2013

Demand Paging

Whenever a program is executed it is required to be loaded into main memory. This loading can be done by two methods:

1) By loading the entire program into main memory. But Problem with this technique is that if user wants to select limited options, whole program will be loaded regardless of user selection.

2) Another Approach is to load only those pages which are currently needed. “The Technique of loading in which only those pages are loaded into main memory which is currently needed is called Demand Paging”. The pages which are not required are not loaded into main memory.