What is Difference Between Pixel and Resolution

What is Difference Between Pixel and Resolution

Pixel vs Resolution

Summary: Difference Between Pixel and Resolution is that pixel is the smallest element in an electronic image. The greater the number of pixels the camera uses to capture a picture, the better the quality of the picture. While Resolution is the number of horizontal and vertical pixels in a display device. A digital camera’s resolution is defined in pixels.

Pixel

A pixel (short for picture element) is the smallest element in an electronic image. The greater the number of pixels the camera uses to capture a picture, the better the quality of the picture. Digital camera resolutions range from about 4 million to more than 16 million pixels (MP).

Usually displays are measured in size(in centimeters and inches). Here we only measure the diagonal size and not the horizontal or vertical size of the screen. There is also another important property of display which is the resolution. Resolution refers to size of the display in terms of pixels. E.g. Resolution of 800×600 pixels means that the there are 800 pixels horizontally and 600 pixels vertically. So therefore there are a total of 480000 pixel in the display.

Pixel is just an element of the picture that plays an important role to complete the image. The word ‘pixel’ was first published by Frederic C. Billingsley in 1965. The measurement of the screen can be described through pixels. Hence, the size of the image also depends on the number of pixels, the larger the number of pixels your image is having the greater the size will be.

Pixel Density

Many of us are not aware of the importance of Pixel Density in displays. It is the thing which describes the sharpness and clarity. Pixel Density is usually measured in PPI (Pixels Per Inch) which refers to number of pixels present per inch on the display. Higher the pixel density higher is the sharpness of the content. Pixel Density is calculated based on the resolution and size of the display.

Pixel Density= Root((Horizontal Number of Pixel^2) + (Vertical Number of Pixel^2))/Screen Size

Resolution

One factor that affects the quality of digital camera photos is its resolution. Resolution is the number of horizontal and vertical pixels in a display device. A digital camera’s resolution is defined in pixels. Resolution is made up of all the elements (pixels) combined together to form a quality image. The greater the resolution is the better you will get the quality of your picture. Resolution describes the elements or pixels in an image. You can measure resolution in three difference ways, Sample per inch (spi, scanners) or Pixel per inch (ppi, monitors) or Dots per inch (dpi, printers).

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Important Considerations When Choosing Your Web Hosting Service

Important Considerations When Choosing Your Web Hosting Service 

Starting of a Business website and tech blog is vital for a perfect growth, while foundation of an online business depends on the hosting services. Since, an online presence has become a must for all types of businesses, thus the choice of the best web hosting company is also crucial. Among many web hosting companies present today, making a choice of the best host depends on various factors listed below. You must read our in in depth beginner’s guide to web hosting.

Selecting the right web host company can be an arduous task. This is more so particularly when you have little experience in this field.When choosing a hosting service, it’s important to not only consider the price but the quality as well. Selecting a professional web hosting company is vital for your website since the quality of service will influence long-term results.

Cost of Service Package

The cost is definitely a significant factor when selecting a hosting package. So, do a little research prior to choosing a web hosting service.

The Overall Management

When you are not familiar with web programming, you should look for hosting packages that will provide you with the possibility to administrate your web site with dedicated interface (Webmin, cPanel among others). A number of applications used in cPanel, for instance, are free and provide a lot of facilities. Don’t forget to ask your chosen provider the installation process when buying a hosting package.

Space & Scalability

The basic service that a web hosting company provides is a space on the web for hosting different websites. The availability of the amount of space and bandwidth according to a hosting plan is a vital point to be considered. Web hosting companies like Hostgator, Webhostingbuzz and Roboshift do a good job at providing unlimited bandwidth, as websites/companies expand and grow in the future.

Number of accounts per server

If it’s a shared server, it’s recommended to be aware of the number of sites that you’ll be sharing the same server with. When there are several web sites on the server, your website has greater chances of loading slowly. You should compare the number of accounts on the server with the number of accounts used by other web hosting companies to have a strong starting negotiation point.
For dedicated servers, always ask if upgrades will be performed – memory, hard disk and CPU among others. Don’t forget to ask your chosen professional IT services provider about your site’s downtime in the event that an upgrade is performed.
 

Website Speed

After hosting a website, the prime feature that binds a user to the website is the speed at which its web pages load. A website should load within seconds or the visitor will move away from the website. So, before buying a plan, ensure that the hosting company uses a high-speed connection to allow your website to show up faster.

Security

Faster loading is an essential feature, but it is useless if your website isn’t secure. A fast website might attract a lot of visitors, but the lack of security features will force most of them to leave the site. So, the host must have plans that offer high security for the personal, financial and private data transferred while access to the site by using secure servers like SSL and others. There is a great video on Youtube that explains SSL that you should check out.

Technical Support

The demand of technical support for the customers or clients of a company is in high skies these days. This facilitates the clients of the company to get quick resolutions for any technical issue encountered, while accessing the service. The company should provide a high quality and convenient support service to solve customers’ queries, available round the clock.

Control Panel

Although a web hosting company is available to assist you in all aspects, but it isn’t always feasible to contact the host. So, the provider must offer a control panel for you to modify or update your website on your own. The panel must offer an easy interface to the website owner.

Email Capabilities

Every business needs dedicated email addresses to be used for different business activities. Thus, before selecting a web hosting company, you must check with the availability of email addresses, amount and ability for aliases use and auto responding ability. File size restrictions are also vital to be considered for receiving and sending files.
 

Add-on Features

The need of online presence for a business and the use of internet services or a website for other purposes has gradually increased. This increasing requirement of websites has led to an increase of the number of web hosts tightening the competition levels. So, to attract more customers, many companies offer various additional features. You must look for a company offering the best services including both the basic and add-on features.
 
Here’s hoping that the above factors will serve as your guide in considering the right web hosting company.All of these tips will help to make lighter work of choosing the most suitable and affordable web hosting service.

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What is Parallel Space.How does parallel space app works?

Parallel Space

Parallel Space is a "container" app for Android devices, it creates a virtualized, isolated environment and allows other apps to running inside. ... So, basically you are running your app on an emulator rather than mobile directly. So, it allows you to have multiple accounts on a virtual environment.

The virtual environment is created by creating something like qemu user mode. The qemu is used to switch between multiple operating systems, or processes from one CPU to the other. So, basically you are running your app on an emulator rather than mobile directly. So, it allows you to have multiple accounts on a virtual environment.

"In parallel space we can add 2 account of any app( like WhatsApp, Instagram,etc) For eg- In WhatsApp you have account from SIM 1 number but you also want to make an account from SIM 2 so you make account but while using u can only use 1 account. So parallel spa helps you to use both accounts simultaneously. You get notifications of both the accounts."

What Is Parallel Space?

Parallel Space is an Android app that allows you to run multiple accounts of any app simultaneously on single Android phone. With parallel space, you can create the dual account of any app. Like you can install two Whatsapp, two Instagram, two Facebook, two Snapchat and multiple accounts of any game.

Parallel Space allows you to have two copies of Twitter running, each with a separate login. Yes there are many social media apps out there that allow you to have multiple accounts simultaneously but with this app, you can truly have them separated.

Parallel Space is an Android app that has one clear goal; to make it easy for users to run the same app or game twice, at the same time. This means that users with a personal and business Facebook account can simply run Facebook twice at the same time, effectively signing in to Facebook with two different accounts at the same time, without having to switch between them. This can be used for Pokemon GO players, serial Instagram snappers and a whole lot more applications. It’s simple and easy to use, without taking up too much space or too much more resources. It’s professional, clean and useful with almost 50 Million installs to boot. So, let’s go ahead and see what all the fuss is about, shall we?

 Play Store link  |  Download Parallel Space APK

Features Of Parallel Space

Run Multiple Account Of any Android App

Small Size: 2MB Only.

Separate Task Manager to Manage apps running in Parallel Space

Storage Manager to Manage App Data

Switch with Swipe option.

Just like the Android apps you might be looking to clone, people can download Parallel Space from the Play Store. Once it is installed, there’s a simple introduction to how the app runs.

How to Use Parallel Space

Open Parallel Space and select the app you want run under Parallel Space.

 If your app isn’t listed, tap the “+” button at the bottom and select the app you want to add from the list of installed apps on your device.

Once you’ve selected the app, a Parallel Space will be created for that app and you’ll be good to go.

Your virtualized apps will appear on the Android recents screen with “(Parallel Space)” suffix, and you can easily multi-task between the real and virtualized version of the app like you’re using two installations.

Cheers! Have fun running multiple accounts/profiles on apps installed on your Android device with Parallel Space.

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Job Profile: Careers in IT : System administrator

System administration refers to the management of one or more hardware and software systems.

The task is performed by a system administrator who monitors system health, monitors and allocates system resources like disk space, performs backups, provides user access, manages user accounts, monitors system security and performs many other functions.

 

Duties of a system administrator

The duties of a system administrator are wide-ranging, and vary widely from one organization to another. Sysadmins are usually charged with installing, supporting, and maintaining servers or other computer systems, and planning for and responding to service outages and other problems. Other duties may include scripting or light programming, project management for systems-related projects.

The system administrator is responsible for following things:

1. User administration (setup and maintaining account)
2. Maintaining system
3. Verify that peripherals are working properly
4. Quickly arrange repair for hardware in occasion of hardware failure
5. Monitor system performance
6. Create file systems
7. Install software
8. Create a backup and recover policy
9. Monitor network communication
10. Update system as soon as new version of OS and application software comes out
11. Implement the policies for the use of the computer system and network
12. Setup security policies for users. A sysadmin must have a strong grasp of computer security (e.g. firewalls and intrusion detection systems)
13. Documentation in form of internal wiki
14. Password and identity management

Cloud computing and sysadmin

Cloud computing is nothing but a large number of computers connected through the Internet/Wan. Cloud computing is now part of technology and sysadmin must lean:

1. Automation software such as puppet, chef, etc.
2. Cloud infrastructure such as AWS, Openstack etc.
3. Network services in cloud such as Content delivery networks (Akamai, CloudFront etc) and DNS servers.
4. Source control
5. Designing best practices for backups, and whole infrastructure.

What is so special about the system administrator account?

The root account has full (unrestricted) access, so he/she can do anything with system. For example, root can remove critical system files. In addition, there is no way you can recover file except using tape backup or disk based backup systems.
Many tasks for system administration can be automated using Perl/Python or shell scripts. For example:

• Create new users
• Resetting user passwords
• Lock/unlock user accounts
• Monitor server security
• Monitor special services etc

Most important skill to a system administrator

Problem solving, period. This can some time lead into all sorts of constraints and stress. When workstation or server goes down, you are called to solve the problem. You should able to quickly and correctly diagnose the problem. You must figure out what is wrong and how best it can be fixed in small amount of time.

Job Summary

Responsible for the technical design, planning, implementation, and the highest level of performance tuning and recovery procedures for mission critical enterprise systems. Serves as a technical expert in the area of system administration for complex operating systems. Recommends the redesign and configuration of operating systems and system applications. Investigates and analyzes feasibility of system requirements and develops system specifications. Identifies methods, solutions, and provides project leadership and management in order to provide a high level of service to the customers of the department. Performs full supervision of Operations staff.

Typical Duties and Responsibilities

1. Manages the day-to-day operations of the PCC host computers by monitoring system performance, configuration, maintenance and repair. Ensures that records of system downtime and equipment inventory are properly maintained. Applies revisions to host system firmware and software. Works with vendors to assist support activities.
2. Develops new system and application implementation plans, custom scripts and testing procedures to ensure operational reliability. Trains technical staff in how to use new software and hardware developed and/or acquired.
3. Supervises Operations staff including hiring, training, evaluating and disciplining. May guide or provide work direction to technical staff, contract staff and/or student employees. Determines appropriate coverage for all hours of operation.
4. Performs troubleshooting as required. As such, leads problem-solving efforts often involving outside vendors and other support personnel and/or organizations.
5. Establishes, maintains and manages users Unix accounts. Installs, modifies and maintains systems and utility software on server computer systems. Provides server support related to other software.
6. Establishes guidelines and methods for the installation and management of the host computer operating systems, disk arrays, fiber channel switches, tape libraries and other components.
7. Ensures high availability and acceptable levels of performance of mission critical host computer resources.
8. Develops procedures to maintain security and protect systems from unauthorized use, acts of nature and user abuse.
9. Develops procedures, programs and documentation for backup and restoration of host operating systems and host-based applications.
10. Develops and coordinates project directions and schedules to maximize benefits and minimize impacts on the customer organizations. Provides leadership in planning and implementation of projects for computer operations and enterprise systems administration.
11. Develops tools, procedures, and training sessions for Operations, Client Support and Systems Development staff to assist with work.
12. Manages the data center and computer host systems including hardware, software and equipment such as air-conditioning system, UPS (uninterrupted power system) and fire protection system.
13. Stays current with technological developments in systems administration technology and recommends ways for PCC to take advantage of new technology.
Positions in this classification may perform all or some of the responsibilities above and all positions perform other related duties as assigned.

Minimum Qualifications

Associate's degree in Computer Science or related discipline. Relevant experience may substitute for the degree requirement on a year for year basis. Three years work experience in complex systems design, programming and systems software and support.

Knowledge of: Programming languages and operating systems; current equipment and technologies in use; Unix system administration, enterprise backup and recovery procedures, and system performance monitoring tools; effective project management techniques; principles and practices of effective management and supervision.

Ability to: Plan, organize and document complex system design activities and to configure systems to be consistent with institutional policies/procedures; communicate technical/complex information both verbally and in writing; establish and maintain cooperation, understanding, trust and credibility; perform multiple tasks concurrently and respond to emergency situations effectively.

Work Environment and Physical Requirements

Work environment includes typical computer related noise levels and paper and equipment generated dust. Exposure to video display terminals occurs on a regular basis. Incumbent is on call to provide support services during off hours. Scheduled night and weekend work is required. Learned physical skill is required for keyboarding and use of peripheral equipment. Moderate lifting.

There are different types of system administrators based on their roles and responsibilities. A bigger company might have different system administrators having different roles, but for smaller company, most of the different roles might be shared by just a few system administrators, or even one single person. Some of the different types of system administrators are:

• Server administrator – maintains the operating system of the servers, and to some extent, the applications as well, such as the mail services, the web services, etc. He is also in-charge of troubleshooting any hardware, operating system or application related problems.
• Network administrator – maintains the network infrastructure, such as the routers and switches, and troubleshoot network-related problems.
  • Database administrator (DBA) – maintains the database system used by organisation. In bigger organisation which uses bigger and more complex databases, there is a DBA which specifically responsible for this role. In smaller organisation, this role would normally be shared by the server administrator

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Set Specific country Target in Google Webmaster Tools for website

Geo targeting or geographic target setting is the option for webmasters to link targeted geographic location of traffic to their sites in Webmaster Tools account. This helps Google to determine the search results for a specific geographic location.

Geographic setting is one of the tools Google uses to determine the top search results for a particular country hence Google search results will vary from country to country for the same keywords.

Domains and Geographic Settings

All the country specific domains like .us (Unites States), .in (India) or .ca (Canada) are by default linked to a particular country and hence there will not be an additional geographic targeting option required for these domains. This means for country specific domains you will not see a “Geographic Target” setting option in your Google Webmaster Tools.

The generic top level domains like .com, .net, .info or .org are not linked with any countries in specific. Hence Google provides an option to add a geographic target for the webmasters owning a generic top level domain.

If there is no geographic location set for a generic top level domain site in Webmaster Tools account then Google uses various other data like server location and information on Google Places before displaying it in the search result pages. If your site is not linked with any geography and you changed your hosting provider then it is recommended that you inform Google about the new location of your server through geographic target setting. This will help Google to re-determine the position of your site in the search results for geographically restricted searches.

How to Set a Geographic Target?

1. Login to your Webmaster Tools account and select the site. You need to have your site verified successfully in order to use this option.

2. Go to 'Search Traffic'

3. Click on 'International Targeting'

4. Set the Geographic target by selecting the country from the drop-down.

Select “choice country” if you do not want to link your site with any of the geographic locations.

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Best power Banks for Smart Phones

Portable Power Banks are comprised of a special battery in a special case with a special circuit to control power flow. They allow you to store electrical energy (deposit it in the bank) and then later use it to charge up a mobile device (withdraw it from the bank). Power Banks have become increasingly popular as the battery life of our beloved phones, tablets and portable media players is outstripped by the amount of time we spend using them each day. By keeping a battery backup close by, you can top-up your devices while far from a wall outlet.

The Power Banks we're talking about are good for almost any USB-charged devices. Cameras, GoPros, Portable speakers, GPS systems, MP3 players, smartphones and even some tablets can be charged from a Power Bank - practically anything that charges from USB at home can be charged from a Power Bank - you just have to remember to keep your Power Bank charged, too!

Power Banks may also be known as Power Stations or Battery Banks.

Power banks store energy in an internal Lithium Ion battery and can charge the mobile and tablets. They are nothing but a special battery encased in special casing along with required circuitry to control the flow of power. That’s how we explain them in a non technical manner. They store the energy in them just like you deposit money in the bank and have a means to charge a device like you withdraw money! That is the perfect analogy. 

Now that the battery capacity of the devices we are using these days has gone too low what we have been expecting it to with a myriad of tasks being performed, there is a need for an auxiliary power supply and that’s where these power banks come into action.

Choosing a power bank

These are some basic guidelines on what kind power banks to buy. It all depends on your individual requirement. If you have the habit of carrying too many devices while on travel, you may need to get yourself a high capacity power bank. Else, a low capacity portable charger would be sufficient. Her are a few tips based on the major points –

Capacity: This is the most important deciding point in choosing a right power bank. Power Bank capacity refers to how much charge is inside a power bank battery. It is measured in mAh or milliamps per hour. But one thing you need to understand that when a power bank is charging your smart phone or tablet, some of the energy is lost in transfer of power. So the real capacity is about 60-65 percent of the battery capacity listed on the power bank. For example a power bank with battery capacity at 2200 mAh has real capacity in the range 1320mAh to 1430mAh. And this is for quality battery, for downgraded battery the loss of power is even more and hence the real capacity would be less than 1320mAh. Should you decide to buy a power bank, keep your own usage in mind. To meet ever growing charging needs of users, many higher mAh units are available today. Higher end power banks can charge almost any type of devices, from laptops, iPads, tablets and smart phones.

Connectors: Pay specific attention to the number of connectors and the type of connector. It would be more advisable to go for a power bank with built-in cable.

Portability: We are buying a power bank because of its portable nature. If you have to carry a huge power bank than your device, it is too impractical.

Price: Power banks which promise higher capacity at a substantially lower price may not be genuine. Most of them use refurbished battery and may not last long. Go for a power bank from a well known brand. Though it may be a bit expensive, it will keep your device safe and give the required performance.

Protective Circuitry: Ensure that your power bank has additional features to protect your device. Pay attention to following –

Short Circuit Protection – This will help keep your power bank and the device safe when the short circuit problems happen.

Over Charging Protection – This feature will let the power bank cut off the supply when your device is charged fully. Thus, it will be useful in cases of the device being left for charging and forgotten.

Temperature Protection – This will help identify the cases of device overheating while charging the device.

Certification: Check for the UL certification of the device. It will ensure that the power bank you have been buying meets all standard quality requirements.

Best power Banks for smartphones

Xiaomi Mi 16000 mAh Power Bank:

Xiaomi Mi started a trend to offer a good product at very affordable prices with its smartphones and they have carried that philosophy in their other products as well. The 16,000 mAh power bank comes in a metal case and when fully charged has enough juice to recharge a normal phone at least 5 times.

Anker 2nd Gen Astro Mini 3200mAh Power Bank: Anker was founded in 2009, the brainchild of a group of friends working at Google. Fast forward a few years and we’re now the industry leader in mobile power. Anker is the first power bank brand in North America. This Anker 3200mAh power bank is for your basic charging needs. It is very compact and helps you use your smartphone in critical situations when you need to make or take an important call and your smartphone has run out of battery juice. This 3200mAh external battery can charge your Apple iPhone 6 or iPhone 5S/5C more than once, the Nexus 5 once, the Samsung Galaxy S5 0.8 times, Galaxy Note 3 0.7 times, HTC One M8 0.9 times and the iPad mini 0.5 times.

Jackery 6000mAh Power Bank：Jackery Brand mobile battery chargers go the distance. From sports fans to students, moms to mountain climbers, Jackery empowers people on the go. The power bank has single USB charging slot, and it assures full protection from any charging malfunctioning. There are four different colors to match your iPhone: Black, gold, orange, and silver while writing this. Jackery Bar is the smallest portable external battery with 2.1A output designed for extending mobile device battery life. It includes a high-energy density, fast-charging, compact design, and smart safety protection circuit. Jackery delivers beautiful design at affordable prices along with great customer service. The Jackery Bar is often used with leading smartphones and tablets like Samsung Galaxy, Apple iPhone, Apple iPad, and more. Jackery® Bar Performance for iPhones: 200%-300% battery life, Input: 5V/1A, Input charging time: 6-8h via Standard USB or AC adapter (not included); Output: 5V/2.1A; Compact Size: 3.8 x 1.8 x 0.9 inches; Weight: 5.5 ounce; 18- month warranty.

 

Lepow U-Stone Series 12000mAh Power Bank: This Lepow Brand power bank– Red Dot Award Winner for its unique and timeless design, Faster recharging speed of 2.1A for a quick 7 hour charge (please use a 2.1A wall charger). Great energy conversion – higher than 85% for better efficiency, Biodegradable packaging made from recycled materials. U-Stone Package includes the Lepow U-Stone, Micro USB flat cable, and user manual. Apple adapters-30 pin, lightening and wall charger not included.

Zendure A2 6000mAh Power Bank: Zendure USA Inc. was founded in 2013 by Tom Haflinger and Bryan Liu. The company’s mission is to deliver top-quality consumer electronics that exceed consumer expectations using high-end materials, premiere product development partners and user-centric design. The pocket-friendly A2 is our smallest portable charger, but with super-high-density battery cells, it’ll keep your phone charged long after the day is done. The Zendure A2 6000mAh external battery is highly durable, compact and lightweight. This power bank also has an auto-on feature which starts charging your device automatically after connecting it.

EasyAcc 10000mAh Power Bank: EasyAcc Accessory exists to please not to trouble. To make it easy as it uses and looks, The EasyAcc 10000mAh external battery is compact and ultra slim. It is attractive and is available in 6 different colors. This 10000 mAh portable charger is capable of charging the Samsung Galaxy S5 2.5 times, iPhone 5S 4.5 times, iPhone 6 nearly 4 times, iPad Air nearly once, HTC One M8, Moto X and Nexus 5 nearly 3 times, LG G3 and Sony Xperia Z3 more than 2 times.

RAVPower 3rd Gen Deluxe 16750mAh Power Bank: RAVPower has made numerous powerbanks or external battery packs with each version improving upon the other. 

One of the most important things about RAVPower is their reputation and reliability. The RAVPower 16750mAh portable charger is capable of charging various devices like AppleiPhone 6, iPhone 6 Plus, Apple 5S/5C, iPad Air mini, Samsung Galaxy S5, Galaxy S4, Galaxy Note 4, Galaxy Note 3, Galaxy Tab 4 Pro, Google Nexus, HTC One (M8), LG G3, MOTO X, Sony Xperia etc.

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How does WhatsApp technology works?

Whats App is Chat application. WhatsApp is a texting service between mobile phones as a replacement for the regular SMS text messages. Over millions users are active worldwide using the Whatsapp service. Whatsapp uses an internet connection between phones. The service is available for iPhone, Blackberry, Android and Nokia Symbian60-phones.

The major difference between regular SMS text messages and Whatsapp text messages is that Whatsapp is free: You use the internet connection on your phone (wifi or part of you mobile data package depending on subscription or pre paid type).

We call them Instant Messaging.  This means the messaging between sender and receive should happen in real time, unlike email (offline).

So you need to first understand challenge here to understand how chat apps work.  If you store something on database, then you pass again to another user, it becomes offline (not in real time).  If you pass any message and it stores and also pass at same to other user, it becomes IM (Instant messaging). 

Now in development, there are different PROTOCOLS that help achieve things.

For Emails its: SMTP, POP3 etc.

For Chat its: XMPP (Extensible Messaging and Presence Protocol)

It is protocol based on another format named XML (like html, not exactly, but to give you idea).  Using XMPP protocol, XML as communication medium and setting up this on a server, that host it and helps pass all communication and also setup logic on this server (Basically coding).  So there are many server created with protocol XMPP like eJabber.

Interestingly, WhatsApp is related to "Yowsup" , a Python library.  Python is a programming language on which Quora, YouTube etc. are built! You can find this Yowsup library on tgalal/yowsup.

So now lets put together all above information.

A user A has internet and a client application (whats app) installed on say Android phone), A user B has internet and has same client application (Whatsapp) installed on his iPhone. (So basically cross platform).

A types message "Hi" to B.  The message is passed via Web Services to XMPP server, The XMPP server has list of all WhatsApp user, based on unique phone number, it will detect B and XMPP server will then send message "Hi" to B with web service.  B will recieve this message on iPhone.  In between there will coding done with business rules on server, database level and on client applications as well. 

Whatsapp is implemented at server end over the protocol XMPP. Exactly it is done on XMPP lite which is well established open source chat engine. 

What is the Technology behind WhatsApp?

WhatsApp uses a customized version of the open standard Extensible Messaging and Presence Protocol (XMPP) upon installation. WhatsApp automatically compares all the phone numbers from the device's address book with its central database of WhatsApp users to automatically compares all the phone numbers from the devices address book with its central database of WhatsApp users to automatically add contacts to the users WhatsApp contact list.

What is Extendible Messaging and Presence Protocol (XMPP) ?

The Extensible Messaging and Presence Protocol (XMPP) is an application profile of the Extensible Markup Language (XML) for streaming XML data in close to real time between any two or more network-aware entities. The address format for XMPP entities was originally developed in the Jabber Open Source Community in 1999. It functions between or among servers, and facilitates near-real-time operation. The Protocol may eventually allow internet users to send instant messages to anyone else on the Internet, regardless of differences in Operating systems and browsers. 

XMPP is sometimes called the Jabber protocol, but this is a technical misnomer. Jabber, an IM application similar to ICQ (I Seek You) and others, is based on XMPP, but there are many applications besides Jabber that are supported by XMPP. The IEEE XMPP working group, a consortium of engineers and programmers, is adapting XMPP for use as an Internet Engineering Task Force (IETF) technology. 

In addition, the Messaging and Presence Interoperability Consortium (MPIC) is considering XMPP as an important interoperability technology. Eventually, XMPP is expected to support IM applications with authentication, access control, a high measure of privacy, hop-by-hop encryption, end-to-end encryption, and compatibility with other protocols.

Database management

For the database management Mnesia DB comes into play. Mnesia is a multiuser distributed DBMS which happens to be the default DB of ERLANG. Thus by using Mnesia, the app is able to achieve quicker request responses, thereby improving the overall efficiency.

FreeBSD is the operating system upon which WhatsApp is laid upon. Improvising on the ERLANG based applications and optimizing FreeBSD, WhatsApp is able to achieve better throughput. For storing multimedia files, the app uses an exclusive web server YAWS.

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