The Virtual Memory Concept

Virtual Memory is a cost effective solution to slake the thirst of memory hungry applications for a seamless experience with your operating system. To understand the concept of virtual memory you need a little knowledge about the memory organization and working. There are basically two types of memory you need to know. Random Access Memory (RAM) is faster but costly. Memory like hard disk is slower but relatively cheaper. Virtual memory is a stratagem to utilize the hard drive memory to achieve enhanced performance from the random access memory.

Whenever you run multiple programs/applications in your desktop, you will be working on only a portion of a particular application at an instant. Therefore it is a waste of resource to load the entire memory required for a particular application into the limited size random access main memory. In a virtual memory environment each page of a process is brought to main memory only when it is needed on demand.

Virtual Memory Block Diagram Working

Data is stored in any memory in the form of binary digits. The operating system handles memory management in the form of chunks of memory called pages. A page is nothing but a contiguous block of memory. One process might require multiple pages of memory but only a few pages might be active at a time. Virtual memory uses a technique called demand paging to effectively use the available RAM memory. Every page has an address which may be a virtual or logical address. The main memory is divided into equal size chunks called page frames and each page frame has a unique physical address. So whenever a page needs to be accessed, the operating system has to translate the virtual address into a physical address and this is done by a Memory Management Unit (MMU) with the help of mapping in a page table. The virtual address corresponding to a page is mapped to a physical address corresponding to a page frame in main memory. Whenever a page is not in memory the operating system fetches the page from hard disk in response to a page fault exception. The operating system usually makes a prediction based on past history using intelligent algorithms regarding those pages that are least likely to be needed again and places them in the hard disk.

A-GPS for the Novice

Assisted GPS is an improved version of conventional GPS and it has revolutionized mobile navigation systems across the globe. The A-GPS system relies upon an assistance server to accurately resolve the location of a device. A-GPS system is commonly used in mobile phones to provide real time navigation services. The Global Positioning System works on the principle of trilateration to determine the coordinates of a point on earth. In this principle a satellite is considered to be at the center of a sphere and the mathematical treatment of three such spheres/satellites gives the intersections of the spheres which are used to determine the coordinates. By including one more sphere/satellite in the analysis the point can be located more precisely. The distance between the point on earth and the satellite is computed by transmitting a packet of data tagged with the sent time and by subtracting this from the time the packet was received, we get the time of transit. Assuming the packet traveled at the speed of light, we can estimate the distance of the satellite which serves as the radius of the sphere.
Assisted GPS Working Block Diagram
The standalone GPS system is susceptible to atmospheric conditions and multipath errors which tend to prolong the time to first fix. This is not appropriate for real time navigation and emergency applications. A-GPS offers a solution to this problem with an architecture that makes use of data connectivity to an Assistance server located at a place with strong signal connectivity with the satellites. There are two possibilities here.

  • The assistance server may transmit orbital parameters and atomic time information to the mobile phone via the network. The GPS receiver in the mobile phone correlates this data with the fragmentary data received directly from the satellites thereby increasing its sensitivity and resulting in a quicker time to first fix.
  • The mobile phone with limited processing capabilities can delegate the processing function to the more sophisticated assistance server by sending the weak fragmentary data to the processing server that has good satellite signal and receive the position information from the server through the network.

A-GPS is a feasible option to provide navigational services in an urban environment with tall buildings and high radio interference. On the flipside the service provider will charge the subscriber for network data traffic using GPRS/3G.

Linux Server Time Zone $TZ Problem - Yesterday Date Script

I encountered a peculiar problem in a shell script that was used to find the yesterday's and tomorrow's date using the environmental variable TZ. The script that was previously written to find yesterday's date on a server that was located in EDT time zone was

YesterdayDate=`TZ="EDT+24" date`

But unfortunately the code failed to give the correct date of yesterday and instead it gave today's date. I thought of digging deep into this issue and logged in to a linux server to investigate the matter. After some long manipulations I observed something.

Unix server time zone $TZ

BST is 1 hour ahead of UTC $ YesterdayDate=`TZ="BST+23" date`

The script "EDT+24" gave only GMT/UTC time and inorder to get the correct timezone I needed to add the offset value for the particular time zone. After I made the changes the script seems to be working fine.

EDT is 4 hours behind of UTC $ YesterdayDate=`TZ="EDT+28" date`

CDT is 5 hours behind of UTC $ YesterdayDate=`TZ="CDT+29" date`

MDT is 6 hours behind of UTC $ YesterdayDate=`TZ="MDT+30" date`

PDT is 7 hours behind of UTC $ YesterdayDate=`TZ="PDT+31" date`

I'm still a bit confused as to why the $TZ is behaving so unexpectedly.

Note: I'm just a novice and not an expert in Unix or Shell Scripting. I just wanted to share my experience with timezones on linux servers.

Nokia 5130 Express Music - Mobile Review

Nokia 5130 Xpress Music Colors

Last week I wanted to buy a mobile phone for my father and I was hunting for an economical music phone with camera and GPRS. Since I was buying it for my dad, I preferred Nokia because of the user friendly interface their phones have. When I inquired my friends, almost everyone suggested the Nokia 5130 Xpress music phone. I was convinced with the looks of the phone and bought it.


The Price of the phone is the crowd puller. With a 2.0 Megapixel Camera, 1GB microSD card storage, Bluetooth, GPRS and a sleek design, Nokia 5130 is a smart buy option.

I would give 9 out of 10 for the design and form factor. Everything is neatly packed, smoothly finished and custom fabricated with the buttons ideally located for a perfect music phone. The backlighting effect is appreciated.

I'm a person who prefers phones with a bigger display. Nokia 5130 display area is not the largest ever but definitely satisfying for a budget phone with compact design.

The music quality and stereo effects are good to hear in the headphone. The keypad is robust and comfortable to type.

Initially when the phone was introduced people complained about hanging problems and phone getting automatically restarted issues. Its been a week since I bought the phone and there are no issues till now.


The battery was a bit of a let down by Nokia. When I opened the back panel and found that the battery is the same old BL-5C that created a hullabaloo not long ago was psychologically disappointing.

The microUSB data cable that came along with the phone was incredibly short and there is absolutely no way I can place my phone on the table once I plugged it in the PC's USB slot.

Bluetooth is the only plausible data transfer option. The microUSB cable is short and there is no software CD in the package.

Inability to connect to Wi-Fi networks, lack of office tools, cheesy loud speakers at high volume, etc are desirable features missing on the phone.

What is a VPN?

Virtual private network is a cost effective solution for companies to extend network connectivity to its employees in every corner of the globe. Consider a company sends an employee to another country that is far away from the company headquarters on a secret mission. There must be some way for the employee to retort to the company and access the private network of the company in a secure way. The company cannot install a private network across countries because it would be expensive. Therefore they must find a way to communicate with the employee in a secure manner using the internet. This is were a virtual private network comes in to the picture. A VPN is a private network connection that is virtual in the sense that there is no dedicated private physical network connecting the entities. But the traffic is sent via the public internet that is vulnerable to attack in a secure manner. Private traffic is carried on the public network in a safe manner using several technologies like encryption, firewalls, authentication, IPsec, etc. VPN gives an organization the freedom to clandestinely communicate with its outbound employees in an economical fashion.

Solar Energized Housing Complex

A housing complex in Kolkata is designed to tap solar energy and utilize it for household applications. It is also possible to feedback energy to the grid when excess power is available. The residents will also get paid for the power returned to the grid. This project is the first of its kind in the country and is expected to inspire the nation. This photo voltaic technology is already in use in Europe and other developed nations. Photo voltaic technology basically involves materials that emit electrons when light is incident on them. Our former president Abdul Kalam had also urged the young students of our country to research on photovoltaic energy. The solar tiles embedded on top of the roof in this complex are able to generate 2KW of power. When there is a shortage of solar power the grid will supply power and when solar power is surplus the reverse process happens. Tapping solar energy will bring down the internal temperature of houses during summer. Power will be available even when there is a conventional power cut. The most crucial aspect of solar powering homes is that it will reduce the amount of carbon emission which will have an impact on global warming. Cost is a major constraint in implementing the system in countries like India but things are looking up for the future.

WaiverWire announces free Stimulus Package

WaiverWire - the leading NFL resource on the web has launched a free tool known as "The Stimulus Package" to let NFL fans join the fantasy football bandwagon. The 2009 NFL season promises a visual treat to the fans and gives a bird's eye view of the NFL action on the web. Those who cannot afford the premium packages can access the tools and statistics offered by WaiverWire free of cost by signing up for "The Stimulus Package". My love for fantasy football is undying and my favorite NFL player is Knowshon Moreno. The high flying running back is a class apart and I love him for his on field acrobatic adventures. I'm expecting a brilliant show by my man this season and hopefully Denver can make it to the top this time. But my money is on Nnamdi Asomugha and he might turn out to be the extraordinary performer this season. Throughout this season I'll be keeping an eye on player statistics and rankings delivered by WaiverWire in the hunt for the best player of NFL 2009. People at my office often talk about their favorite players and flaunt their NFL knowledge. Now that I have signed up with WaiverWire, I can make use of the player comparison feature and give an apt repartee to them.

Pasanga - Film review

Pasanga is an interesting film that touches the depths of childhood and school life. The film starts off in a wobbly manner with the kids being portrayed as naughty bugs and some of the scenes just fail to connect us to our own childhood. The director could have made a better attempt in depicting school life in my opinion. But the story settles down nicely interwoven with childhood egos and family sentiments. The love between Vimal and Vega is the most beautiful aspect of the movie. They are wacky yet passionate and capture our hearts with their sublime performance. The film has a strong message for parents. Parents must keep their own differences apart and encourage their children to succeed. The director has exhibited his true talent in the scene between the heads of both the families near a pond. The music is satisfactory with "Oru Vetkam Varuthe" and "Iraiva Iraiva" still lingering in my mind. Pasanga is a complete family entertainer and it is worth a watch.

Pen drive virus

Yesterday I got a pen drive from my friend and inserted it into my PC. The pen drive had some video clips and pdf books which my friend had put from his system. Unfortunately when I opened the pen drive on my system, my anti-virus software alerted me about some viruses and worms in the pen drive. So I selected the heal option and some of the viruses where quarantined. After cleaning up I again opened the pen drive. To my surprise all the folders and files were missing and the drive was empty. I was very much disappointed because it had important data and I was eager to access them. When I checked the properties, it showed that the drive is full. So I got an idea. I just right clicked on the pen drive icon and clicked on search option. Voila! All the files became visible in the search results. I copied them from the search window in to my own hard drive. What a misery with viruses and worms..!

Waiverwire Real Time Football Analysis Tools

Football is a challenging game for the people who work behind the scenes to help their teams win matches. They need real time alerts and information as soon as possible to stay ahead in the race. WaiverWire is the ultimate source of fantasy football rankings, analysis softwares, drafting tools, news and updates. They have introduced a new In- Season Pass for just $9.99 in order to get access to premium information and expert utilities for the entire 2009 season. The package includes real time player alerts and updates, fantasy football analysis, over 100 feeds from local beat writers, player projections and comparisons and access to Waiver Wire’s Fantasy Social Network and community forum. New graphically enhanced visual analysis tools and customized SOS by position are the added benefits. This is a special offer for the inaugural season and you can't afford to miss this opportunity. By signing up with waiverwire you become eligible for unlimited benefits to improve the performance of your team. Every successful team out there has a secret behind its success. The In- Season Pass could be your secret of success because no other website offers so much benefits as waiverwire. Waiverwire believes in the power of information and it doesn't miss even a single bit of information.

Bling Bling Techellery

Everyone loves to wear jewellery to augment their beauty and portray their fashion statement. Golden jewellery is the most common and affordable to the middle class. The rich might opt for diamonds, platinum, pearls... etc apart from gold. But the price of gold has increased enormously making it difficult for the middle class to buy. I guess it will be a good idea to wear techellery. Techellery is the fusion of technology and jewellery. It is the new fashion trend gaining popularity. If you wish to propose to a girl how about the idea of presenting her a USB heart pendant. Philips and Swarovski have come up with a plethora of wacky tech accesories for youngsters. Head phones are not only meant for hearing audio but they will also serve as colorful hair bands with studs for a glittering scalp. The most famous of them is the digital pendant which is available in the key chain and chain form. Jewellery will no longer be only a passive aesthetic structure but also serve multiple purposes in the form of techellery. Now it is time for you to grab your own piece of ornamental gizmo and make a style statement with these ubiquitous gadgets.

Haptics holds the key

Haptics is the science of sensing and maneuvering objects by touching. The field has made good progress and things are looking up. It is a fusion of virtual reality and communication mechanism by which you can feel remote objects in a 3D environment just by looking at your computer screen.

If haptics advances at this rate there is a possibility of performing remote surgeries on humans. A doctor can get the feel of the patients body and organs from a remote place and manipulate the movements of a robot to perform the surgery. A lot of work has to be done on this to ensure precision and prevent mishaps. Scientists believe remote surgery will be possible in the future. Haptics has already taken hold in several fields like teleoperators, gaming and several day to day applications. The user can get a feedback about the weight,dimensions and the hardness of the virtual objects. Research is going on to incorporate Peltier effect devices whose temperature can be controlled by applied voltage to get a feel of the temperature of the object. Also the texture of the objects can be felt from variations in friction. Haptic interfaces with sensors can help persons with impaired hands to get a feel of objects. The real challenge will be to get the technology ready to perform remote surgeries in order to save valuable human lives.

The other side of Engineering

Engineering graduates here in Tamilnadu who don't perform well in academics are forced to join BPOs and other lower paid jobs. Many companies have a minimum eligibility criterion in order to get placement. But most of the students in third class studying in third class engineering colleges which do not have campus placement struggle to get placed in an IT company. They end up in call centers where their co-workers are from the arts & science stream who have not spent too much for their degree. Experts say that it is always good to choose the domain for your wards that is most suitable for them. Students forced in to the engineering stream lack interest and don't get good marks in their exams. When they come out of college life they don't get better jobs. But if you allow your children to select what they desire to study they'll perform well.

Don't use Mobile Phones while driving

In recent years the number of accidents because of people talking on the phone while driving is high. The cause for this is now biologically proved. It is due to the interference between the two actions and the brain fails to multitask simultaneously.

A group of researchers have found that the act of speaking and thinking what to speak overloads the brain and puts excess demand on the resources of the brain. This is something similar to the CPU usage in our computers. They came to this conclusion based on two experiments. Some 50 people were tested and asked to detect various shapes on a screen while listening and responding on the phone. In the other experiment they were asked to track a fast moving object with the help of the mouse. The measurements revealed that the subjects were more diverted while preparing to reply or speaking than while listening. They seemed slightly at ease while listening. The experiments were conducted in a circular surround sound environment and the speakers were hidden from the subjects. There will be a significant drop in their concentration levels of a person while talking on the mobile phone during driving which could be fatal. Prevention is always better than cure....

Waiting for a turnaround

Life in recession is tricky and confusing. Nobody knows how it started and when it will end. It is hard to plan for the future in this gloomy situation and no one has a clue. Almost every industrial sector looks battered in this global economic downturn and it has spread across continents. The blame game never seems to cease and it is very unlikely to spot a silver lining. I always used to wonder where has all the money gone. People have mixed opinions about a recovery. For a guy like me who knows nothing about the markets or the economy there are no simple answers for all my stupid questions I guess. For the moment I'll keep my fingers crossed and wait for a revival.

Web Hosting Chronicles

Today almost everyone hooked to the internet is interested in owning a website to generate some kind of revenue that will augment their income. All that you need to do is search for free web hosting services to publish your website. Web hosting rating is an excellent place to start your web journey in order to know about the quality of services provided by major web hosting companies. Honest ratings and unbiased reviews are the trademark of where each and every web hosting provider's credentials are dissected for you to see. You will be able to find companies that provide services according to your budget and requirements. Make your decision only after browsing through all the information regarding web hosting at web hosting rating.

Naan Kadavul review

Naan Kadavul is a film that exposes some of the hardest truths of life. Arya and Pooja have come up with performances of their lifetime. The film is pragmatic yet sluggish and tends to gather momentum as time goes on. The suspense is intriguing and the audiences have to wait till the end to taste the extreme bitterness exploded by Bala at the climax. The climax sent shivers down my spine but it best fits the movie and made me stand up and applaud in silence after being petrified for a few minutes. Bala has tried to strike a balance between atheism and belief which has worked perfectly. The film is suitable for both believers and non-believers which is fascinating but it all depends on how you take it. Anyway overall the movie was good but certain things were forced on us by the director and we have to bear with them. The climax stands out and I loved it.


All those engineers who thought chemistry is a school boy thing think again, Nanotechnology could well be the next big thing. Modern day gadgets like iPods to even nano cars are the early outcomes of nanotechnology. But the field promises more and has applications in medicine, security, environment and many more domains.

Nanotechnology aims at miniaturization and involves redesign and manipulation of atoms which are the basic building blocks of all matter. It is a well known fact that diamond and graphite are allotropes of carbon and rearranging the atomic structure of one of them can result in the other one. Therefore by rearranging the atoms of a bulk material we can develop a nano material. Nanotechnology helps in developing tiny robots called nanobots which help in perfoming surgeries for replacing worn out tissues. Nano-coatings are known to be transparent, scratch proof and dirt repellant. Even Cancer tissues can be pictured by imaging in oncology using nanoparticles. In a few years time nanotechnology will have its roots spread in all industries.

In India the field is just sixteen years old and a few universities are offering the course in post graduate. Several companies are planning investments in this area considering future developments. I think its time to gear up for the nano revolution and good to learn about it.

Beware of wardrivers

A wardriver is someone who is on the move with a laptop or a smart phone in search of wireless networks with bad intentions. If he detects a WiFi network that is open and not password protected he could possibly unleash his vicious activities on the web. The wardriver can send anonymous emails, browse the web using the owner's IP and access secret information with almost no risk of being identified. A WiFi network has a range of 20-30m normally and this is enough for the wardrivers to make merry. It is virtually impossible to trace the wardriver through the web because the IP may point to the network owner. In the past several incidents have been reported to be triggered from unsafe wireless networks of educational institutions and public places. The process is not as difficult as hacking. A piece of software downloaded from the internet can do the job. If they are allowed to persist data theft will become common and there will be no room for privacy. Strict laws and creating awareness among the internet owners is the need of the hour.