Agrani Bank Limited - Senior Officer (ICT), 2017

Agrani Bank Limited - Senior Officer (ICT), 2017

1.     Question: Explain Type 1 and Type 2 hypervisors in virtual machine operating system.

What is Hypervisor?            

A Hypervisor also known as Virtual Machine Monitor (VMM) can be a piece of software, firmware or hardware that gives an impression to the guest machines(virtual machines) as if they were operating on a physical hardware. It allows multiple operating system to share a single host and its hardware. The hypervisor manages requests by virtual machines to access to the hardware resources (RAM, CPU, NIC etc) acting as an independent machine.

Now the Hypervisor is mainly divided into two types namely
Type 1/Native/Bare Metal Hypervisor
Type 2/Hosted Hypervisor

Type 1 Hypervisor

• This is also known as Bare Metal or Embedded or Native Hypervisor.
• It works directly on the hardware of the host and can monitor operating systems that run above the hypervisor.
• It is completely independent from the Operating System. 
• The hypervisor is small as its main task is sharing and managing hardware resources between different operating systems.
• A major advantage is that any problems in one virtual machine or guest operating system do not affect the other guest operating systems running on the hypervisor.

       Examples:

          VMware ESXi Server
          Microsoft Hyper-V
          Citrix/Xen Server

Type 2 Hypervisor

• This is also known as Hosted Hypervisor.
• In this case, the hypervisor is installed on an operating system and then supports other operating systems above it.
• It is completely dependent on host Operating System for its operations
• While having a base operating system allows better specification of policies, any problems in the base operating system a ffects the entire system as well even if the hypervisor running above the base OS is secure.

         Examples:
         VMware Workstation
         Microsoft Virtual PC
         Oracle Virtual Box         

  Question: Difference between method overloading and overriding in Java.

There are many differences between method overloading and method overriding in java. A list of differences between method overloading and method overriding are given below:

No.	Method Overloading	Method Overriding
1)	Method overloading is used to increase the readability of the program.	Method overriding is used to provide the specific implementation of the method that is already provided by its super class.
2)	Method overloading is performed within class.	Method overriding occurs in two classes that have IS-A (inheritance) relationship.
3)	In case of method overloading, parameter must be different.	In case of method overriding, parameter must be same.
4)	Method overloading is the example of compile time polymorphism.	Method overriding is the example of run time polymorphism.
5)	In java, method overloading can't be performed by changing return type of the method only. Return type can be same or different in method overloading. But you must have to change the parameter.	Return type must be same or covariant in method overriding.

3.      Question: Explain inode data structures in linux OS.

      The inode (index node) is a data structure in a Unix-style file system that describes a file-system object such as a file or a directory. Each inode stores the attributes and disk block locations of the object's data. A directory contains an entry for itself, its parent, and each of its children.

     Inode: Data structure for bookkeeping 

   – List of Blocks

    – File or Directory

    – Link Count 

   – Other information…owner/permissions 

4.      Question: What is the working procedure of AJAX?

Ajax is based on HTML, CSS, JavaScript, DOM, and XML.

HTML/CSS
HTML/CSS is website markup language for defining web page layout, such as fonts style and colors.

JavaScript
JavaScript is a web scripting language. JavaScript special object XMLHttpRequest that was designed by Microsoft. XMLHttpRequest provides an easy way to retrieve data from web server without having to do full page refresh. Web page can update just part of the page without interrupting what the users are doing.

Document Object Model
Document Object Model (DOM) method provides a tree structure as a logical view of web page.

XML                       
XML is a format for retrieve any type of data, not just XML data from the web server. However you can use other formats such as Plain text, HTML or JSON (JavaScript Object Notation). and it supports protocols HTTP and FTP. XMLHttpRequest is used heavily in AJAX programming.

As you can see in the above example, XMLHttpRequest object plays a important role.

1. User sends a request from the UI and a javascript call goes to XMLHttpRequest object.
2. HTTP Request is sent to the server by XMLHttpRequest object.
3. Server interacts with the database using JSP, PHP, Servlet, ASP.net etc.
4. Data is retrieved.
5. Server sends XML data or JSON data to the XMLHttpRequest callback function.
6. HTML and CSS data is displayed on the browser.

5.     Question: Explain with examples: candidate key, foreign key and horizontal scaling.

Candidate Key - The candidate keys in a table are defined as the set of keys that is minimal and can uniquely identify any data row in the table.

Foreign Key - A foreign key is an attribute value in a table that acts as the primary key in another another. Hence, the foreign key is useful in linking together two tables. Data should be entered in the foreign key column with great care, as wrongly entered data can invalidate the relationship between the two tables.

6.     Question: Explain  the components of data center.

The major components of a data center can be broken down into a few categories: power, cooling, security, fail safe measures and room for growth.

Power: Next to cooling equipment, power is perhaps the most important detail of a data center. All of your web hosting servers and colocation equipment run off of dedicated power source, power is the holy grail of every data center. More to the point, beyond simply being able to provide power to colocation equipment through PDU’s, every data center worth its salt needs to have redundant/backup power sources to ensure server and overall service uptime. Without redundant power supplies, i.e. backup power generators, a data center is only as good as the local city grid it operates off of. As we know, those city grids fail often. 

Cooling: Just as important as power, proper cooling in a data center allows your colocation servers, networking gear and other general web hosting equipment to function properly without overheating. A good way to think about how critical cooling is to data center operations, is to think about the old 1997 Dell laptop you used to own. When you let it rest on your lap, it would heat up to the point of being uncomfortable. This happened because the laptop didn’t have proper ventilation and the fan running inside of it designed to keep the system cool, wasn’t strong enough. The same happens in a data center. Without proper ventilation – raised floors to evenly spread cooling, hot/cold isles – your server would burn up and cease to function. It is important to note, just as power supplies within a data center need to be redundant, cooling also needs to be redundant.

Security: Beyond physical colocation servers and dedicated web servers, data centers function with a high level of security needs. Why? All of the servers, be they Cloud hosting servers or shared hosting accounts, house critical client data. Due to that, the security systems of a data center need to function around the clock. A good data center maintains 24/7/365 security staff, closed loop surveillance cameras, finger print access and visitor log books. Moreover, data center security is a matter of physical security, i.e. being out of harm’s way. Physical data center security means building a data center outside of noted flood zones, outside of fault lines and outside of noted tornado alleys/hurricane paths.

Fail Safe Measures: Another major component of data centers is fail safe measures for all data stored within that data center. This means all data center hosts need to maintain and operate a backup data center wherein all data is replicated and stored. It is highly important for data center providers to supply consumers with a backup geo-diverse redundant data center facility in case of main point of operations downtime.

Room For Growth: This one is pretty self-explanatory. Investing in colocation or dedicated servers is a long term investment. As a long term investment, your investment needs to be able to grow with your demands as your company expands. All data center providers need to supply clients with the room they need to grow.