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: 

I) Object Base Data Models: Object based data models defines a database in terms of objects, their properties, and their operations .Objects of same behavior and structure belongs to a class and classes are organized into hierarchies. The operations of each class are specified in terms of predefined procedures called methods. Commonly used object based data models are:

What is Distributed Data Processing (DDP) ?

Distributed Data Processing (DDP)

It is a configuration in which many geographically dispensed or distributed independent computers are connected by means of computer networks. In this type of configuration Programs, data and other resources are shared among several users who are geographically far away from one another. This provides the facility of better resource use to the end users.

This approach is different from centralized system because computers are installed at different locations and each of them performs independent data processing. Each computer in DDS is designed for a specific task.
 
Advantages of Distributed Data Processing

1) In Distributed data processing resources can be used in centralized or non centralized manner.

2) Smaller or complex jobs can be easily handled. Small jobs are done with the help of Personal Computers whereas complex jobs are performed by complex systems.

Types of Operating System

Type	Definition	Example
Batch Processing System	Data along with programs collected and grouped and is processed on later date.	Pay Roll Systems, Stock Control Systems, Billing Systems.
Real Time Systems	These are those operating systems in which input immediately affects the outputs and timing is critical.	Chemical Processing Systems, Nuclear Power Plant Control Systems.
Real Time Transaction	These are those Operating Systems in which input immediately affects the output but timing is not critical.	Air Ticket booking Systems, Hotel Booking Systems.
Proprietary OS	Proprietary OS is licensed under legal right of the copyright holder with the intent that the licensee is given the right to use the software only under certain conditions, and restricted from other uses, such as modification, sharing, studying, redistribution, or reverse engineering	Windows OS all Versions
Open Source OS	These are those OS Software whose Source code is free to users. Anybody can help I development and modifications.	Linux, UNIX

Difference between NTFS and FAT file Systems

Characteristics	NTFS	FAT
Stands For	New Technology File System	File Allocation Table.
Partition Size	NTFS support size of files and volumes, up to 2^64 bytes (16 Exabyte’s or 18,446,744,073,709,551,616 bytes).	FAT partitions are limited in size to a maximum of 4 Gigabytes (GB) under Windows NT and 2 GB in MS-DOS.
Naming Conventions	File and directory names can be up to 255 characters long, including any extensions.	It follows 8.3 naming convention. The name of a file or directory can be up to eight characters long, then a period (.) separator, and up to a three character extension.
Suitable Volume size	It is not recommended to use NTFS on a volume that is smaller than approximately 400 MB, because of the amount of space overhead involved in NTFS. This space overhead is in the form of NTFS system files that typically use at least 4 MB of drive space on a 100 MB partition.	FAT file system should not be used in drives or partitions of over 200 MB. This is because as the size of the

Difference between High Level and Low Level Formatting

Sr. No.	High Level Formatting	Low Level Formatting
1	High-level formatting is the process of setting up an empty file system on a disk partition or logical volume and, for PCs, installing a boot sector. It creates the file system format within a disk partition or a logical volume. This formatting includes the data structures used by the OS to identify the logical drive or partition’s contents.	Low-level formatting is the process of outlining the positions of the tracks and sectors on the hard disk, and writing the control structures that define where the tracks and sectors are. It really creates the physical format that defines where the data is stored on the disk.
2	It can be done during OS installation or new partition creation.	This is intended to be the permanent foundation of the disk, and is often completed at the factory.

CPU Scheduling Techniques

Round-Robin Scheduling

It is the CPU Scheduling Technique specially designed  for the time shared systems. This Technique is similar to FCFS Technique but the difference is that processes are switched at a regular interval of time and the regular internal is called time quantum.The can be from 0 to 100 milliseconds.

The ready queue is used in a circular fashion. The CPU is allocated to each process for a regular interval of time of 1 time quantum each new process is added to the tail ready queue. CPU scheduling picks first process from ready queue, set a timer to interrupt after 1 time quantum and then process is dispatched.If the burst time of process is less than a time quantum then it will automatically release the CPU.The average waiting time a round Robin policy is often high.

Consider the following ready queue of processes.
Process               Burst time
   P1                           10
   P2                           20
   P3                           5


Let the time Quantum be 5 miliseconds. The Gantt chart will be as given below

What is Process?

 Any Program that is under execution is called a Process e.g. scanning an image is a process.

For the completion of a process resources are required. These resources are allocated to process either when process is created or is under execution. For Example you have typed a page in Microsoft Word and you want to print it, as you give print command the print process is created and it requires Printer as resource. If any other process is using the printer then your page will be queued and will be printed when first process of printing is complete. A process may have sub processes which are called child processes.A Process can demand only those resources which are available e.g. if 8 resources are available than process can demand all 8 resources but 9th resource can't be demanded.

What are Semaphores?

These are like integers but has the following three difference from them:
1) Its value can be initialized as integer but only increment or decrement operations are allowed and its current value can't be read.
2) If any thread decrements its value and result is negative then thread itself can't continue until any other thread increments the Semaphore.
3) If any thread increments Semaphore and their are another threads waiting ,one of the thread gets blocked which was in waiting list.


Explanation : Consider the example of a Cyber Cafe which has 20 cabins and is used by one person at a time for the prevention of dispute user requests a cabin from front counter to use PC.When user work is over he returns to counter makes payment and indicates that now one cabin is free.If no cabin is free than user has to wait until any cabin is free.

The person sitting at front counter only knows the no. of occupied cabins ant not the particular cabin which is occupied.if somebody leaves the cabin the no. of occupied cabin's no. is decremented and if somebody requests a cabin the no. of occupied cabin's incremented.

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.

This technique has the advantage that less memory is consumed and more processes can be loaded at the same time which utilizes more resources. Demand paging is very similar to swapping. The whole program resides in secondary storage and when process execution is required, it is swapped into main memory and in spite of loading whole program only currently required pages ware swapped.

To perform this task swapper is used which is called pager. It does not swap any program until it is required in the main memory. Additional hardware is also required to check that which pages are in memory and which pages are on disk.

Directory Implementation in Operating System

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 

2) Hash Tables: In technique Directories are saved in same linear fashion but a hash table is used. It takes a value that is returned from file name and returns a pointer

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.

The Problem associated with this technique is that every time we have to calculate the file size and then to allocate the contagious

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.
 

Problems Associated:
1) Files can be accessed in a serial fashion. E.g. to access n^th   block of disk we have to start from beginning until n^th block comes.

2) Another problem is that extra 4 bytes are consumed from each block for the storage of pointers. This problem is resolved by the use of clusters. Cluster is a combination of blocks into multiples. e.g. 5 blocks of disk can be used as single cluster and only one pointer will be required for 5 blocks.

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 n^th entry in the index block points to n^th 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.

The main advantage of using this technique is that it support direct file access. Another advantage is there is no external fragmentation. There is no need to re define the file size.

Problem associated with this technique is that what should be the size of index blocks? If we use one block for per file index and file is too large than it will not be possible to maintain index on single disk block. To overcome this problem linked index scheme is used where index block are linked together to form a large file index.

How to recover hidden folders from Virus Effected Pen Drive

This is a very common problem that arises many times that we plug our Pen Drive to a Laptop or PC and its Contents got hide. It’s a situation of real shock because media may contain very important information or data for the preparation of which you have spent your plenty of Hours. Here is a simple and very quick trick by following which you can easily recover your Data.

Steps Included:

This is a Simple two-step Process:

      1) Copy and Paste below given code to notepad file and save it as unhider.bat file name or with any file name having .bat extension.

@echo off

@echo ***********************************************************

@echo *Application Compiled by allroundexpert.blogspot.com*

@echo ***********************************************************

Difference between HTTP and HTTPS

Parameter	HTTP	HTTPS
Acronym for	Hypertext Transfer Protocol	Hypertext Transfer Protocol Secure
Description	It is the request response based application protocol in client-server model & is designed to work within the framework of Internet Protocol Suit.	It is a Secured version of HTTP to allow secure transactions. E.g. Net banking. It wraps the entire communication within SSL, thus, encryption starts before any data is sent.
Ports Used	This Protocol works on TCP/IP Port No. 80 or 8080	This Protocol Uses TCP/IP Port No.443 for data communication.
Encryption	This Protocol is a stateless protocol and do not uses any encryption method.	HTTPS uses long term public and secret keys to exchange a short term session key to encrypt data flow between client and server.

Difference between IPv4 and IPv6

Characteristics	IPv4	IPv6
Deployed	1981	1999
Address Size	It uses 32 bit addresses	It uses 128 bit addresses.
Address Format	Dotted Decimal Notation: 192.168.1.1	Hexadecimal Notation: FFFE:F200:3204:0B00: 0122:4555:8001:AB00
Prefix Notation	192.168.1.1/24	2FFE:0200:6234::/48
Number of Addresses	232= ~4,294,967,296	2128 = ~340,282,366, 920,938,463,463,374, 607,431,768,211,456
Compatibility	It is less compatible to mobile networks.	It is much compatible to mobile networks.
Uses	It is used in 99% of the networks.	It is used only in remaining 1% of networks.

Difference between Public Private and Hybrid Cloud

Parameter	Public Cloud	Private Cloud	Hybrid Cloud
Definition	If a cloud infrastructure is made available to general public or a large industry group than it is called Public Cloud.	If a cloud infrastructure is operated solely for an organization than it is called Private cloud.	Composition of two or more clouds (Private, Public, and Community) is called hybrid Cloud. It is the composition of at least one public cloud and at least one private cloud.
Users	Can be used by any internet user on pay per usage basis.	Used by only members of the organization.	It is used by the organizations that are willing to push part of their workloads to public cloud.
Advantage	Good test/development environment for applications that scale too many servers.	Security least is very low because cloud users are very much limited.	Operational flexibility, run mission critical on Private cloud, tests on public cloud.

Difference between Wi-Fi and Wi-Max

Parameter	Wi-Fi	Wi-Max
Acronym for	Wireless Fidelity	World Interoperability for Microwave Access
Description	It is a wireless technology that allows any electronic device to exchange and transfer data wirelessly.	It a wireless technology which delivers carrier class, high speed wireless broadband at low cost and covering large distance than Wi-Fi.
IEEE Standard	IEEE 802.11	IEEE 802.16
Implementation	It is basically an implementation of wireless Local Area Connection within a small building, a college, or an institutional building.	It is a wireless broadband metropolitan technology whose objective is to interconnect houses, buildings, or even hot spots to allow communication between them or with other networks.
Cost	Can be implemented by using low cost access pints.	Wi-Max technology requires costly infrastructure.

Difference between AT89C51 AT89C52 and AT89C2051

Parameter	AT89C51	AT89C52	AT89C2051
Flash Memory Size	4K Bytes of In-System Reprogrammable Flash Memory	8K Bytes of In-System Reprogrammable Flash Memory	2K Bytes of Reprogrammable Flash Memory
Endurance	1,000 Write/Erase Cycles	1,000 Write/Erase Cycles	10,000 Write/Erase Cycles
Data Memory Size	128 X 8 bit internal RAM	256 X 8 bit internal RAM	128 x 8-bit Internal RAM
Operating Voltage	5V (up to 6.6V)	5V (up to 6.6V)	2.7V to 6V
Programmable I/O Lines	32	32	15
Timers/Counters	Two 16 bit	Three 16 Bit	Two 16 bit
Interrupt Sources	Six	Eight	Six