K-Developers

How To Set up OpenVPN in Ubuntu

As noted above, some providers have dedicated VPN clients for Ubuntu (or Linux), but others simply supply manual configuration guides for setting up Ubuntu’s native Network Manager (which absolutely fine, as Network Manager is a great VPN client.)<br/><br/>Even when providers do not have Ubuntu (or even Linux) specific setup instructions on their websites, OpenVPN is easy to setup. This means that any OpenVPN service can be used with Ubuntu, regardless of what support available for this from your provider.<br/><br/>1. Download and install the Ubuntu OpenVPN packages for Network Manager by opening a Terminal window and typing:<br/><pre class="lang:default decode:true ">sudo apt-get install network-manager-openvpn openvpn</pre><br/>Note that Network manager should already be installed. If for some reason it is not, install it by entering:<br/><pre class="lang:default decode:true ">sudo apt-get install openvpn network-manager-openvpn network-manager-openvpn-gnome</pre><br/>2. Restart the Network Manager. This can be done by restarting Ubuntu or logging out and in again, but the easiest way is to enter the following at the Terminal command prompt:<br/><pre class="lang:default decode:true ">sudo restart network-manager</pre><br/>3. Download the VPN provider’s OpenVPN configuration files (.ovpn and .crt), and Extract them to a convenient location.<br/><br/><a href="http://k-developers.com/wp-content/uploads/2016/01/ubuntu.png"><img alt="ubuntu" class="size-full wp-image-179 aligncenter" height="548" src="http://k-developers.com/wp-content/uploads/2016/01/ubuntu.png" width="606" /></a><br/><br/>4. Open Network Manager and click VPN Connections -> Configure VPN…<br/><br/><a href="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-vpn-connections.png"><img alt="ubuntu-vpn-connections" class="size-full wp-image-180 aligncenter" height="233" src="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-vpn-connections.png" width="423" /></a><br/><br/>5. Click on ‘Add’.<br/><br/><a href="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-network-connections.png"><img alt="ubuntu-network-connections" class="size-full wp-image-181 aligncenter" height="173" src="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-network-connections.png" width="411" /></a><br/><br/>6. Select ‘OpenVPN’ from the drop-down menu and click ‘Create…’<br/><br/><a href="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-connection-type.png"><img alt="ubuntu-connection-type" class="size-full wp-image-182 aligncenter" height="434" src="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-connection-type.png" width="736" /></a><br/><br/>7. Ensure the ‘VPN’ tab is selected, and enter the VPN server address supplied by your provider in the ‘Gateway’ field. Under ‘Authentication’, select ‘Password’ from the dropdown ‘Type’ menu, and enter your account details.<br/><br/>Then Click on the ‘CA Certificate Field’ and navigate to the .crt file at the location you unzipped the OpenVPN config files to in Step 2. Click on ‘Advanced’…<br/><br/><a href="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-openvpn-settings.png"><img alt="ubuntu-openvpn-settings" class="size-full wp-image-183 aligncenter" height="619" src="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-openvpn-settings.png" width="647" /></a><br/><br/>8. Check ‘Use LZO data compression’. Note that is step may not be required, or may require different settings depending on your VPN provider. Click ‘OK’ and ‘Save’, and setup is complete!<br/><br/><a href="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-openvpn-advanced.png"><img alt="ubuntu-openvpn-advanced" class="size-full wp-image-184 aligncenter" height="429" src="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-openvpn-advanced.png" width="556" /></a><br/><br/>9. To start the VPN connection, simply go to Network Manager -> VPN Connections -> your connection<br/><br/><a href="http://k-developers.com/wp-content/uploads/2016/01/ununtu-connections-2.png"><img alt="ununtu-connections-2" class="size-full wp-image-185 aligncenter" height="233" src="http://k-developers.com/wp-content/uploads/2016/01/ununtu-connections-2.png" width="423" /></a><br/><br/>You are now connected! Notice that the Network Manager taskbar icon now has a tiny padlock on the bottom right, to let you know the VPN connection is active.<br/><br/><a href="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-vpn-log.png"><img alt="ubuntu-vpn-log" class="size-full wp-image-186 aligncenter" height="233" src="http://k-developers.com/wp-content/uploads/2016/01/ubuntu-vpn-log.png" width="378" /></a><br/><br/>Hurray! you are good to go. :)<br/><h2></h2>

Linux OpenVPN Ubuntu How To Set up OpenVPN in Ubuntu

Top 10 Websites To Learn Programming Online For Free 2015

If you are new to the world of programming and web development, it makes sense to start by using all the free resources available online and mastering the techniques without leaving your room. The days are past us when only those who enrolled in top computer science institutes and colleges mastered the art of programming, and later got to dominate the computer world. Today everyone has the same potential, and even better chance to learn and master programming languages without spending too much and waiting in the long queues.<br/><br/>If you want to take the computer world by storm like Bill Gates and Mark Zuckerberg, you need to have a very strong background in computers and programming since very young age. To make things easier and help you in the pursuit of success, I will show you 10 interactive websites that will guide you through your new path into programming world!<br/><br/><hr /><br/><br/> <br/><h4>1) <a href="http://www.codecademy.com/" target="_blank">Codecademy</a></h4><br/>Codeacademy is the place to go if you aren’t quite sure where to start. It is indisputably the most famous website to teach you to code interactively, thanks to its helpful interface and well-structured courses. Upon visiting the main page, you can already start tasting the programming right away, with its motivating on-screen console. Pick a course that Codecademy offers from Web Fundamentals, PHP, JavaScript, jQuery, Python, Ruby and APIs.<br/><br/>Inside each lesson is a panel that explains necessary code and instruction. Another panel allows you to get your hands dirty by writing acceptable code, then checking if you are doing the right thing. Don’t worry about making mistakes, as both instruction and code panels will warn you of errors, and provide hints. It is as if there’s a kind teacher right beside you.<br/><br/><hr /><br/><br/> <br/><h4>2) <a href="http://www.codeavengers.com/" target="_blank">Code Avengers</a></h4><br/>Code Avengers is designed to make you love programming. Though it only offers HTML5, CSS3 and JavaScript course for now, each of the courses is carefully designed to truly entertain you while levelling your programming skills painlessly. At the end of each lesson you also get to play a mini game to release your cumulated stress, and keep you going for longer.<br/><br/>Code Avengers has a gradual approach to interactive learning. It does not explain too much knowledge that isn’t essential for beginners, just a bit of code and playful instruction, making things very easy to digest. You also get to play with the code, then see the impact of the changes immediately. It is carefully crafted with the beginner’s comfort in mind.<br/><br/><hr /><br/><br/> <br/><h4>3) <a href="http://w3schools.com/" target="_blank">W3Schools.com</a></h4><br/>W3Schools.com is one of the common and the world’s largest web development site. The site is best for both beginners and the experts. W3Schools.com is optimized for learning, testing and training. The site delivers 1000+ examples of different codes like JavaScript Examples, HTML DOM Examples, jQuery, jQuery Mobile Examples, AJAX Examples, PHP Examples, ASP Examples, SVG Examples, ADO Examples, XSL Examples, RSS Examples, .NET Examples and more. These examples must be solved to improve your coding knowledge and basic understanding.<br/><br/>Here you will get varieties of reference and tutorials too, to sharpen your knowledge and make code more familiar to you. This site is the most beloved by college students because of its chapter wise interactive learning manner which students ever like.<br/><br/><hr /><br/><br/> <br/><h4>4) <a href="http://www.codeschool.com/" target="_blank">Code School</a></h4><br/>Code School is the next quality website you should land on. Unlike most interactive learning sites, Code School offers more in-depth courses to train and turn you into an expert with the industry’s best practices.<br/><br/>Almost all courses are aggressively polished with impressive design and informative screencasts, though the challenges after the screencast might bit a bit hard for amateurs. Luckily, there are hints and answers to refer to. While most of the offered courses are free, certain ones will require you to spend $25/month to access the entire course including all screencasts and challenges, and also all other courses in Code School.<br/><br/><hr /><br/><br/> <br/><h4>5) <a href="http://teamtreehouse.com/" target="_blank">Treehouse</a></h4><br/>Treehouse is a must visit site for novice programmers with a sense of purpose. It's courses are more project-oriented than language-oriented, so they are perfect for novice programmer with a planned purpose, such as building a website, or an application. For example, the Websites course is all about building a responsive website, interactive website or even WordPress theme – a very practical and efficient way to master related languages. Nonetheless, they have released a plethora of foundation courses with a video-then-quiz approach.<br/><br/>For Treehouse, every course is divided into different stages or modules, and beyond every first stage the learner will be invited to pay a monthly subscription fee of $25 to access all courses with 650+ videos, and an exclusive Treehouse Members Forum as a bonus. If you are serious about your programming future, you could subscribe the $49 monthly plan to obtain in-depth interviews with leading industry pros and cutting-edge workshops.<br/><br/> <br/><br/><hr /><br/><br/><em>Before we move on take a look at <a href="http://k-developers.com/webdesign/top-10-free-text-editors-for-developers-2015/" target="_blank">Top 10 Text Editors for Developers.</a> also known as source code editors, that are specifically designed for programmers or developers for writing  and experimenting with the source code.</em><br/><br/><hr /><br/><br/> <br/><h4>6) <a href="http://www.learnstreet.com/" target="_blank">LearnStreet</a></h4><br/>LearnStreet is truly friendly and enjoyable, and most importantly, free. If you are that kind of personnel who do not fancy playful design and prefer to deal with cold hard codes, LearnStreet is probably your thing. It currently offers JavaScript, Python and Ruby courses at beginner level. With a click on the ‘Start Course’ button you will start the lesson with an exercise, a code interpreter and a glossary panel (for new programming terms).<br/><br/>LearnStreet adopts command prompt-styled code interpreters with human language to explain function and encourage you whenever possible, the kind of command prompt you want for your own local machine. However, the code interpreter could be as rude as standard command prompt, as most of the times it requires you to type in the absolute same code and content it asks for.<br/><br/><hr /><br/><br/> <br/><h4>7) <a href="https://www.udacity.com/" target="_blank">Udacity</a></h4><br/>Udacity is the unification of insightful video lectures and improved quizzes to achieve the interactive feel for students, so it’s ideal for those who don’t like to read but rather get explanations from industry professionals such as Google employees. Udacity is probably not your starting point, but a virtual university to further your study.<br/><br/>You will be given a screencast from pros discussing the topics and instructions, then you will take either logic or programming quizzes to strengthen your understanding or forge it into a skill. The good thing about Udacity is it provides more videos than any other site, and the instructors are either real-life professors or industry veterans.<br/><br/><hr /><br/><br/> <br/><h4>8) <a href="http://beta.scratch.mit.edu/" target="_blank">Scratch 2.0</a></h4><br/>Scratch is something even easier to understand. Previously an offline software that allow kids to create, upload and share their projects proudly, Scratch is now fully online with its 2.0 successor.<br/><br/>It’s not about programming though, but a combination of visual blocks of commands that tell assigned objects how to behave, such as telling the cat to move 10 steps, or yell ‘meow’ when it touches the owner’s leg. By using this visual programming method, the young programmers will form a habit of breaking a problem into smaller blocks, and solve them one by one logically.<br/><br/><hr /><br/><br/> <br/><h4>9) <a href="http://www.codehs.com/" target="_blank">CodeHS</a></h4><br/>At this point all websites you read here are mainly dedicated to web development and computer science, but CodeHS is one with simple and fun game programming lessons that involve problem solving, JavaScript, animation, data structures, game design and puzzle challenges.<br/><br/>The advantage of CodeHS is it teaches you to think, and solve a problem like a programmer with its first course, Programming with Karel. The lessons are fun as you will learn how to use the code to move the dog, Karel to complete given tasks and puzzles like picking up ball and building a towel. It plants a solid concept of programming and the way it solves the problem systematically in your mind.<br/><br/><hr /><br/><br/> <br/><h4>10) <a href="http://www.khanacademy.org/cs" target="_blank">Khan Academy</a></h4><br/>Although Khan Academy’s courses are not as structured as CodeHS, it serves as an open playground for both novice and amateurs particularly interested in learning drawing, animation and user interaction with code. It does not preach any specific programming language, but the code pattern it adopts can be applied anywhere, as a majority of languages share the similar programming pattern.<br/><br/><hr /><br/><br/> <br/><h2>Conclusion</h2><br/>As we all know that the world is changing and utilizing the new technologies. Taking advantage of all the free resources listed above is definitely the way to go and develop a skill set to dominate in the computer world. These websites are the best options to learn programming by saving your time as well as money.

Dev Tools Learn Coding Online Programming Web Design Top 10 Websites To Learn Programming Online For Free 2015

Top 10 free text editors for Developers 2015

<h3 class="crosshead"></h3><br/><strong>First things first,</strong> choosing a text editor can be tricky if you are new to programming. Although there are too many of them available in the market, each packed with unique set of features and flavour, but if you have very particular requirements you may find this list very helpful. We present you the list of top 10 text editors with plenty of features, free of cost and used by top developers worldwide.<br/><h3 class="crosshead">01. <a href="http://www.techradar.com/downloads/notepad" target="_blank">Notepad++</a></h3><br/><figure class="captioned-image"></figure><br/><ul><br/>	<li><strong>Platform</strong>: Windows</li><br/></ul><br/>We admit there's a whiff of nostalgia about this entry, given that Notepad++ was one of the earliest text editors we used on Windows. But the app deserves its place on this list, because it can still compete with the best of them. For no money whatsoever, you get a capable (if sometimes workmanlike) editor with plenty of features, and you can also mess about with the interface to make it better suit your requirements.<br/><h3 class="crosshead">02. <a href="https://atom.io/" target="_blank">Atom</a></h3><br/><figure class="captioned-image"></figure><br/><ul><br/>	<li><strong>Platform</strong>: OSX 10.8 or later, Windows 7 & 8, Linux</li><br/></ul><br/>Launched in 2008, GitHub has become the code storage and development site of choice worldwide, and so any tool it releases is going to cause a big stir.<br/><br/>That's certainly been the case with Atom. Dubbed "a hackable text editor for the 21st Century", it's designed to be simple to use out of the box, but also easily expandable using hundreds of packages.<br/><br/>Since launching in invite-only private beta early last year, it's now fully open source and available to download for free.<br/><h3 class="crosshead">03. <a href="http://brackets.io/" target="_blank">Brackets</a></h3><br/><figure class="captioned-image"></figure><br/><ul><br/>	<li><strong>Platform</strong>: Windows/OS X/Linux</li><br/></ul><br/>Adobe's open-source text editor is created from the code that builds the web, and the developers note that if you can code <em>in </em>Brackets, then you can code <em>on </em>Brackets. In other words, although you initially get a simple, usable editor, seasoned programmers should be able to hack it to their liking.<br/><h3 class="crosshead">04. <a href="http://www.vim.org/">Vim</a></h3><br/><figure class="captioned-image"></figure><br/><ul><br/>	<li><strong>Platform</strong>: Windows/OS X/Linux/Android/iOS</li><br/></ul><br/>Vim is essentially the text editor people flock to when they look at the others on this list and consider them toys for newbies. There's a pretty steep learning curve, due to its overtly techie nature; but if you can cling on or are just looking for something more powerful to work with, you'll find plenty to like in Vim's flexible tools, customisation and macros, and efficiency-oriented commands.<br/><h3 class="crosshead">05. <a href="https://www.gnu.org/software/emacs/">Emacs</a></h3><br/><figure class="captioned-image"></figure><br/><ul><br/>	<li><strong>Platform</strong>: Windows/OS X/Linux</li><br/></ul><br/>There are various incarnations of Emacs but one of the most often-used is <a href="https://www.gnu.org/software/emacs/">GNU Emacs</a>; a free, extensible, customisable text editor. It's one of the most powerful editors out there and as such takes a while to learn your way around, but if you have very particular requirements you may find this is the one for you.<br/><h3 class="crosshead">06. <a href="http://komodoide.com/komodo-edit/">Komodo Edit</a></h3><br/><figure class="captioned-image"></figure><br/><ul><br/>	<li><strong>Platform</strong>: Windows/OS X/Linux</li><br/></ul><br/>If you don't need all the features of a full IDE, you can get the text editor from Komodo IDE for free. Komodo Edit is a multi-language editor that does multiple selections, auto-complete, tracks changes and has a Markdown viewer.<br/><h3 class="crosshead">07. <a href="http://icecoder.net/" target="_blank">ICEcoder</a></h3><br/><figure class="captioned-image"></figure><br/><ul><br/>	<li><strong>Platform</strong>: Windows/OS X/Linux</li><br/></ul><br/>ICEcoder is an open-source code editor that lets you work directly within the browser, whether you’re online or offline. Very lightweight, you can install it and start using it almost instantly. Despite its size, it contains many great features you'd expect from a code editor, including broken tag indicators, highlighting themes and secure login.<br/><h3 class="crosshead">08. <a href="http://www.coffeecup.com/html-editor/">CoffeeCup Free HTML Editor</a></h3><br/><figure class="captioned-image"></figure><br/><ul><br/>	<li><strong>Platform</strong>: Windows</li><br/></ul><br/>Here's another great choice for beginners looking for a simple, free text editor. CoffeeCup Free HTML Editor is the free version of the <a href="http://www.coffeecup.com/html-editor/" target="_blank">full version</a>, and so missing a few tools (CSS menu design, FTP upload) but there are plenty of powerful editing tools, a local Help file to walk you through the more complicated parts, and you can also upload your page to CoffeeCup's S-Drive platform, where it will host it for free.<br/><h3 class="crosshead">09. <a href="http://bluefish.openoffice.nl/">Bluefish</a></h3><br/><figure class="captioned-image"></figure><br/><ul><br/>	<li><strong>Platform</strong>: Windows, OS X, Linux</li><br/></ul><br/>Bluefish is a text editor with plenty of designer-friendly tools and options. Among the goodies on offer are syntax highlighting (ASP.NET, CSS, HTML, JavaScript, PHP and more are supported), code folding, powerful find and search and replace tools and autocompletion. Bluefish also supports document templates; has wizards to add CSS, forms, tables, forms, audio and video objects; and quick tag editing and easy previewing of the current document.<br/><h3 class="crosshead">10. <a href="http://www.actiprosoftware.com/products/apps/codewriter" target="_blank">Code Writer</a></h3><br/><figure class="captioned-image"></figure><br/><ul><br/>	<li><strong>Platform</strong>: Windows 8</li><br/></ul><br/>Windows tablets hardly look set to blaze past Android and iPads, and the app ecosystem is therefore relatively limited. We're therefore delighted Code Writer exists. The editor boasts a sleek interface that's perfectly suited to the UI formerly known as Metro, and the app provides advanced features such as code outlining, syntax-error flagging, text formatting, and auto-correct. Handily, snapped view is also supported, so you can code while 'researching' things on the likes of Twitter.

Dev Tools Notepad++ Text Editors Web Design Top 10 free text editors for Developers 2015

First things first, choosing a text editor can be tricky if you are new to programming. Although there are too many of them available in the market, each packed with unique set of features and flavour, but if you have very particular requirements you…

Interrupts and Exceptions

<b style="font-size: large; font-family: Verdana; line-height: 1.5;">Introduction</b><br/><br/>Much of the functionality embedded inside a personal computer is implemented by hardware devices other than the processor. For example, serial communication is handled by an Intel 8251A chip (or a 16550AF in newer computers), which is located on the computer's motherboard (usually inside an ASIC) while the keyboard is controlled by a 8042A microprocessor.<br/><br/>Since each device operates at its own pace, a method is needed for synchronizing the operation of the processor with these devices. One solution is for the processor to sit in a tight loop, asking each device about its current state (a method known as polling). When data is available in one of the devices, the processor can then read and process the incoming bytes. While this method works, it has many disadvantages. First, it is very wasteful in terms of processing power, since the processor is constantly busy reading the status of the attached devices instead of executing some useful code. And second, when the rate of data transfer is extremely high, the processor might lose data bytes arriving from the hardware devices.<br/><br/>So, a different approach was devised. Instead of polling hardware devices to wait for their response, each device is responsible for notifying the processor about its current state. When a hardware device needs the processor's attention, it simply sends an electrical signal (hardware interrupt) through a dedicated pin in the interrupt controller chip (located on the computer's motherboard).<br/><br/>The interrupt controller serves as an intermediate between the hardware devices and the processor. Its responsibility is to alert the processor when one of the hardware devices needs its immediate attention. In this case, the processor stops its current activity and jumps to execute a function (interrupt handler) which was previously associated with the calling device (or more accurately, associated with the interrupt vector of the device).<br/><br/>While hardware interrupts have a significant importance, software interrupts also play a major role in the normal operation of the PC. These interrupts are synchronous rather than asynchronous, since they are generated by the processor itself when it encounters an INT instruction inside the code stream. Software interrupts are usually used by the operating system to publish its internal functions, thereby allowing applications to take advantage of these services.<br/><br/>Exceptions belong to a special type of software interrupts. They are generated by the processor itself whenever some unexpected critical event occurs. For instance, a page fault exception (interrupt 14) is triggered when the processor attempts to access a page, which is marked as not-present. The exception handler can then reload the page from disk (virtual memory) and restart the instruction which generated the exception.<br/><br/>Three types of exceptions can be generated by the processor: faults, traps and aborts. When a fault exception occurs, the CS and (E)IP registers which are pushed on the stack, point to the address of the instruction, which generated the exception. This gives the exception handler a chance to fix the condition which caused the exception to occur, before restarting the faulting instruction. Traps are similar to interrupts in the sense that they make the processor push the address of the next instruction to the stack, while aborts neglect to specify the location of the faulting instruction, since they are usually used to indicate severe errors (such as hardware errors or illegal system tables) which are not recoverable.<br/><br/><hr /><br/><br/> <br/><br/><span style="font-family: Verdana; font-size: small;"><span style="font-size: large;"><b>Real-Mode</b></span></span><br/><br/><span style="font-size: medium;"><b>Software Interrupts</b></span><br/><br/>If you've ever programmed for DOS, you probably know that the INT 21h interface has a salient importance in linking applications with operating system services. For instance, calling an operating system function for opening a file, simply requires issuing an INT 21h interrupt with the correct parameters set in the processor registers.<br/><br/>The BIOS (Basic Input Output System) uses a similar software communication mechanism. The INT 10h, 13h and 16h are all interfaces to internal BIOS functions, which control the screen, the disk controller and the keyboard. Instead of accessing hardware devices directly, DOS uses the BIOS services to control the operation of the system. Modern operating systems such as Windows NT drop their reliance upon the BIOS in favor of faster mechanisms (device drivers) for accessing the PC's hardware.<br/><br/>When the processor bumps into an INT instruction, it pushes the address of the next instruction (CS and IP registers) and the contents of its flags register to the stack and then jumps to execute the interrupt handler. This ensures that when the handler code ends, the processor returns automatically to the original code stream (the code which was executing before the interrupt occured).<br/><br/>Here are the precise steps taken by the processor when it encounters an INT instruction:<br/><ol><br/>	<li>Push Flags, CS and IP to the stack (in this order).</li><br/>	<li>Multiply interrupt number by 4 and use the resulting number as an offset into the interrupt table (located at the beginning of the physical address space).</li><br/>	<li>Get far address (CS and IP) of the interrupt handler from the table entry.</li><br/>	<li>Disable interrupts (note that if you wish hardware interrupts to be serviced even when the processor executes inside an interrupt handler, you must issue a STI instruction at the beginning of the handler code).</li><br/>	<li>Jump to execute the handler.</li><br/>	<li>When the handler code ends (an IRET instruction is executed), pop CS, IP and the flags from the stack so that control returns to the currently active application.</li><br/></ol><br/>Many applications (especially TSRs - Terminate and Stay Resident programs) hook software interrupts to supply additional services on top of those offered by DOS and the BIOS. One good example is Netware 3.1, which hooks INT 21h in order to add support for network file operations (such as reading a file located on a remote computer). Other pieces of code (mostly device drivers) hook hardware interrupts to monitor various devices and ensure their proper operation.<br/><br/>To hook an interrupt, a program need only to replace a specific interrupt table entry with the address of its own interrupt handler. Whenever this interrupt occurs, the handler is automatically invoked by the processor. A good programming practice is to place a call to the previous handler inside the interrupt handling function. This ensures that all previously installed hooks will get a chance to handle the incoming interrupt.<br/><br/>Note that when loading an application which uses software interrupts to call operating system services, there is no need to patch the application code with the actual memory addresses of the OS services. Therefore, the operating system can freely relocate its services in memory by simply updating the corresponding interrupt table entries with the new addresses.<br/><br/><span style="font-family: Verdana; font-size: small;"><span style="font-size: medium;"><b>Hardware Interrupts</b></span></span><br/><br/>Hardware interrupts are not very different in behavior. But still, when considering the path traveled by a hardware interrupt from the instant it leaves the hardware device until it reaches the processor, you must take into account the actions taken by the interrupt controller (or the 8259A if you prefer).<br/><br/>When the processor executes an INT instruction, it retrieves the interrupt code from the opcode itself. This code is later used by the processor to index the <b>IVT</b> (interrupt vector table) and find the address of the interrupt handler. On the other hand, when a hardware interrupt is detected, the interrupt controller sends the interrupt code to the processor via the data bus. When the code is finally acquired by the processor (either from the INT opcode or from the interrupt controller) the steps taken are equivalent to those discussed earlier.<br/><br/>Table 1 presents the interrupt vectors occupied by the interrupt controller chips under different operating systems:<br/><table border="0" width="50%" cellspacing="1" cellpadding="4" bgcolor="#A3D9F5"><br/><tbody><br/><tr><br/><th bgcolor="#8FB6DF"><span style="font-family: Verdana; font-size: small;"><i>OS</i></span></th><br/><th bgcolor="#8FB6DF"><span style="font-family: Verdana; font-size: small;"><i>Vectors occupied by the master 8259A</i></span></th><br/><th bgcolor="#8FB6DF"><span style="font-family: Verdana; font-size: small;"><i>Vectors occupied by the slave 8259A</i></span></th><br/></tr><br/><tr><br/><td><center>DOS</center></td><br/><td><center>8h - Fh</center></td><br/><td><center>70h - 77h</center></td><br/></tr><br/><tr><br/><td><center>Windows 95 / 98</center></td><br/><td><center>50h - 57h</center></td><br/><td><center>58h - 5Fh</center></td><br/></tr><br/><tr><br/><td><center>Windows NT</center></td><br/><td><center>30h - 37h</center></td><br/><td><center>38h - 3Fh</center></td><br/></tr><br/></tbody><br/></table><br/><span style="font-family: Verdana; font-size: small;"><span style="font-size: xx-small;">Table 1 - Interrupt vectors occupied by the 8259A chips</span></span><br/><br/><hr /><br/><br/> <br/><br/><span style="font-family: Verdana; font-size: small;"><span style="font-size: medium;"><b>Exceptions</b></span></span><br/><br/>When executing in real-mode, the following exceptions are supported:<br/><table border="0" width="50%" cellspacing="1" cellpadding="4" bgcolor="#A3D9F5"><br/><tbody><br/><tr><br/><th bgcolor="#8FB6DF"><span style="font-family: Verdana; font-size: small;"><i>Exception</i></span></th><br/><th bgcolor="#8FB6DF"><span style="font-family: Verdana; font-size: small;"><i>Vector</i></span></th><br/><th bgcolor="#8FB6DF"><span style="font-family: Verdana; font-size: small;"><i>Condition</i></span></th><br/></tr><br/><tr><br/><td><center>Division by Zero</center></td><br/><td><center>0</center></td><br/><td><span style="font-family: Verdana; font-size: small;">Attempting to execute a DIV or an IDIV instruction with a divisor which equals zero.</span></td><br/></tr><br/><tr><br/><td><center>Debug / Single Step</center></td><br/><td><center>1</center></td><br/><td><span style="font-family: Verdana; font-size: small;">Used in conjunction with the debug registers to indicate a breakpoint hit. The processor also issues this interrupt after executing every instruction when the TRAP flag is set.</span></td><br/></tr><br/><tr><br/><td><center>Breakpoint</center></td><br/><td><center>3</center></td><br/><td><span style="font-family: Verdana; font-size: small;">The INT 3 instruction generates this exception. Since the opcode of this instruction is only one byte long, it is often used by debuggers to set a breakpoint in application code. The debugger needs only to replace the first byte of the instruction with the INT 3 opcode (11001100b) and wait for the breakpoint exception to occur. After the exception handler resumes execution and before returning to the debugged application, the debugger sets the INT 3 opcode to the previously overwritten byte and issues an IRET (interrupt return) instruction.</span></td><br/></tr><br/><tr><br/><td><center>Overflow</center></td><br/><td><center>4</center></td><br/><td><span style="font-family: Verdana; font-size: small;">When performing arithmetic instructions with signed operands, the processor set the OF flag to indicate an overflow. The INTO instruction tests this flag and if it is set - generates an exception.</span></td><br/></tr><br/><tr><br/><td><center>Bounds Check</center></td><br/><td><center>5</center></td><br/><td><span style="font-family: Verdana; font-size: small;">The BOUND instruction is used to verify that an array index does not exceed a certain limit. If the limit is exceeded, an exception is generated.</span></td><br/></tr><br/><tr><br/><td><center>Invalid Opcode</center></td><br/><td><center>6</center></td><br/><td><span style="font-family: Verdana; font-size: small;">Occurs when the processor executes one of the reserved opcodes or uses the LOCK prefix improperly. Can also indicate an invalid operand following an opcode.</span></td><br/></tr><br/><tr><br/><td><center>Device Not Available</center></td><br/><td><center>7</center></td><br/><td><span style="font-family: Verdana; font-size: small;">Attempting to execute a floating-point instruction when there is no coprocessor installed. The EM bit of the CR0 register can be cleared to disable this exception.</span></td><br/></tr><br/><tr><br/><td><center>Double Fault</center></td><br/><td><center>8</center></td><br/><td><span style="font-family: Verdana; font-size: small;">An interrupt occurs which has no corresponding entry in the IVT or a second exception is generated while the processor is executing a previously activated exception handler.</span></td><br/></tr><br/><tr><br/><td><center>Stack Exception</center></td><br/><td><center>12</center></td><br/><td><span style="font-family: Verdana; font-size: small;">Stack operation exceeds offset FFFFh or a selector pointing to a non-present segment is loaded intoS.</span></td><br/></tr><br/><tr><br/><td><center>CS, DS, ES, FS, GS Segment Overrun</center></td><br/><td><center>13</center></td><br/><td><span style="font-family: Verdana; font-size: small;">Word memory access at offset FFFFh or an attempt to execute past the end of the code segment.</span></td><br/></tr><br/><tr><br/><td><center>Floating-Point Error</center></td><br/><td><center>16</center></td><br/><td><span style="font-family: Verdana; font-size: small;">An error with the numeric coprocessor (Divide-by-Zero, Underflow, Overflow...).</span></td><br/></tr><br/></tbody><br/></table><br/><span style="font-family: Verdana; font-size: small;"><span style="font-size: xx-small;">Table 2 - Real-Mode exceptions</span></span><br/><br/>Other exceptions exist only in <b>Virtual 8086 Mode</b>:<br/><table border="0" width="50%" cellspacing="1" cellpadding="4" bgcolor="#A3D9F5"><br/><tbody><br/><tr><br/><th bgcolor="#8FB6DF"><span style="font-family: Verdana; font-size: small;"><i>Exception</i></span></th><br/><th bgcolor="#8FB6DF"><span style="font-family: Verdana; font-size: small;"><i>Vector</i></span></th><br/><th bgcolor="#8FB6DF"><span style="font-family: Verdana; font-size: small;"><i>Condition</i></span></th><br/></tr><br/><tr><br/><td><center>Invalid Task State Segment</center></td><br/><td><center>10</center></td><br/><td><span style="font-family: Verdana; font-size: small;">Indicates that one of the checks made during a task switch failed.</span></td><br/></tr><br/><tr><br/><td><center>Segment Not Present</center></td><br/><td><center>11</center></td><br/><td><span style="font-family: Verdana; font-size: small;">Loading one of the segment registers with a selector to a segment marked as not-present.</span></td><br/></tr><br/><tr><br/><td><center>Page Fault</center></td><br/><td><center>14</center></td><br/><td><span style="font-family: Verdana; font-size: small;">Accessing a supervisor page from user privileged code or attempting to access a page which is marked as not-present.</span></td><br/></tr><br/><tr><br/><td><center>Alignment Check</center></td><br/><td><center>17</center></td><br/><td><span style="font-family: Verdana; font-size: small;">Memory access to an unaligned memory location (can only occur while executing ring 3 code).</span></td><br/></tr><br/></tbody><br/></table><br/><span style="font-family: Verdana; font-size: small;"><span style="font-size: xx-small;">Table 3 - Virtual-Mode exceptions</span></span><br/><br/><hr /><br/><br/> <br/><br/><span style="font-family: Verdana; font-size: small;"><span style="font-size: large;"><b>Protected-Mode</b></span></span><br/><br/>Handling interrupts in protected-mode requires setting up a table in memory known as the <b>IDT </b>(Interrupt Descriptor Table). The IDT is somewhat different from the interrupt vector table that exists in real-mode. Instead of being "stuck" at physical address 0, the protected-mode IDT can float around in the linear address space with absolute freedom (although it is possible to change the address of the IVT while in real-mode, it is incompatible with the implementation of the 8086 processor). The linear address of the IDT is determined by a value set into the IDTR register using the LIDT instruction. Each entry in the IDT is 8 bytes long (as opposed to the 4 bytes entries of the IVT) and can contain one of three gate descriptors:<br/><ul><br/>	<li>A task gate - Causes a task switch to occur.</li><br/>	<li>An interrupt gate - Control is transferred to the interrupt handler with interrupts disabled.</li><br/>	<li>A trap gate - Control is transferred to the interrupt handler (the interrupt flag remains unchanged).</li><br/></ul><br/>The following figure presents the internal structure of a trap gate entry:<br/><br/><img alt="" src="http://www.internals.com/articles/protmode/trapgate.gif" /><br/><span style="font-size: xx-small;">Figure 1 - Structure of a trap gate entry</span><br/><br/>Trap and interrupt gates have much in common since they are both used for control transfers between different privilege levels. The selector and offset fields specified in these gate descriptors are used to locate and execute the interrupt handler code. A control transfer is only permitted to a code residing in the same or a higher privilege level but never to a lower privileged one.<br/><br/><span style="font-family: Verdana; font-size: small;"><span style="font-size: medium;"><b>Software Interrupts</b></span></span><br/><br/>Software interrupts are still widely used by protected-mode operating systems in order to publish their internal services to the external world. However, most of these interfaces are now wrapped by functions and cannot be accessed directly (although it's possible, it's not recommended). For instance, Windows NT uses the undocumented interrupt 2Eh to allow control transfers between its user mode and kernel mode components. Whenever a non-privileged Windows application issues a call to an API function, the system routes the call until it reaches an INT 2Eh instruction. The IDT gate corresponding to this interrupt points to a handler inside ntoskrnl, which performs the required privileged operations on behalf of the application. Windows 95 and 98 use a similar technique to hop between user and kernel mode, but rely upon INT 30h instead of using INT 2Eh.<br/><br/><span style="font-family: Verdana; font-size: small;"><span style="font-size: medium;"><b>Hardware Interrupts</b></span></span><br/><br/>Hardware interrupts in protected-mode behave in the same manner as described in the real-mode section. The only major difference is that when executing in protected-mode, the processor consults its IDT rather than searching the real-mode IVT for the address of the interrupt handler.<br/><br/><span style="font-family: Verdana; font-size: small;"><span style="font-size: medium;"><b>Exceptions</b></span></span><br/><br/>Most of the information which was presented in the previous sections, applies to protected-mode as well. However, exception 13 (General Protection Fault) has a wider meaning in protected-mode and can indicate additional conditions than those defined for real-mode.<br/><br/>That's it. More information about the implementation of interrupts and exceptions in protected-mode can be obtained from the "Pentium Processor.<br/><br/>

Computer Organisation Interrupts and Exceptions

IntroductionMuch of the functionality embedded inside a personal computer is implemented by hardware devices other than the processor. For example, serial communication is handled by an Intel 8251A chip (or a 16550AF in newer computers), which is loc…

Ripple Carry Adder

<h3>Ripple Carry Adder</h3><br/>Multiple full adder circuits can be cascaded in parallel to add an N-bit number. For an N- bit parallel adder, there must be N number of full adder circuits. A ripple carry adder is a logic circuit in which the carry-out of each full adder is the carry in of the succeeding next most significant full adder. It is called a ripple carry adder because each carry bit gets rippled into the next  stage. In a ripple carry adder the sum and carry out bits of any half adder stage is not valid until the carry in of that stage occurs.Propagation delays inside the logic circuitry is the reason behind this. Propagation delay is time elapsed between the application of an input and occurance of the corresponding output. Consider a NOT gate, When the input is “0” the output will be “1” and vice versa. The time taken for the NOT gate’s output to become “0” after the application of logic “1” to the NOT gate’s input is the propagation delay here. Similarly the carry propagation delay is the time elapsed between the application of the carry in signal and the occurance of the carry out (Cout) signal. Circuit diagram of a 4-bit ripple carry adder is shown below.<br/><br/><a href="http://k-developers.com/wp-content/uploads/2015/12/ripple-carry-adder.png"><img alt="ripple-carry-adder" class="size-full wp-image-126 aligncenter" height="325" src="http://k-developers.com/wp-content/uploads/2015/12/ripple-carry-adder.png" width="694" /></a><br/><br/> <br/><br/>Sum out S0 and carry out Cout of the Full Adder 1 is valid only after the propagation delay of Full Adder 1. In the same way, Sum out S3 of the Full Adder 4 is valid only after the joint propagation delays of Full Adder 1 to Full Adder 4. In simple words, the final result of the ripple carry adder is valid only after the joint propogation delays of all full adder circuits inside it.<br/><h4>Full Adder</h4><br/>To understand the working of a ripple carry adder completely, you need to have a look at the full adder too. Full adder is a logic circuit that adds two input operand bits plus a Carry in bit and outputs a Carry out bit and a sum bit.. The Sum out  (Sout) of a full adder is the XOR of input operand bits A, B and the Carry in (Cin) bit.  Truth table and schematic of a 1 bit Full adder is shown below<br/><br/>There is a simple trick to find results of a full adder. Consider the second last row of the truth table, here the operands are 1, 1, 0 ie  (A, B, Cin). Add them together ie 1+1+0 = 10 . In binary system,  the number order is 0, 1, 10, 11……. and so the result of 1+1+0 is 10 just like we get 1+1+0 =2 in decimal system. 2 in the decimal system corresponds to 10 in the binary system. Swapping the result “10” will give S=0 and Cout = 1 and the second last row is justified. This can be applied to any row in the table.<br/><br/><a href="http://k-developers.com/wp-content/uploads/2015/12/i-bit-fill-adder-truth-table.png"><img alt="i-bit-fill-adder-truth-table" class="size-full wp-image-127 aligncenter" height="329" src="http://k-developers.com/wp-content/uploads/2015/12/i-bit-fill-adder-truth-table.png" width="582" /></a><br/><br/> <br/><br/>A Full adder can be made by combining two half adder circuits together <em>(a half adder is a circuit that adds two input bits and outputs a sum bit and a carry bit).  <a href="http://k-developers.com/wp-content/uploads/2015/12/half-adder-full-adder-circuit.png"><img alt="half-adder-full-adder-circuit" class="size-full wp-image-128 aligncenter" height="179" src="http://k-developers.com/wp-content/uploads/2015/12/half-adder-full-adder-circuit.png" width="559" /></a></em><br/><br/> <br/><h4>Full Adder using NAND or NOR logic</h4><br/>Alternatively the full adder can be made using NAND or NOR logic. These schemes are universally accepted and their circuit diagrams are shown below.<br/><br/><a href="http://k-developers.com/wp-content/uploads/2015/12/full-adder-using-NAND-logic.png"><img alt="full-adder-using-NAND-logic" class="size-full wp-image-129 aligncenter" height="294" src="http://k-developers.com/wp-content/uploads/2015/12/full-adder-using-NAND-logic.png" width="504" /></a><br/><br/><a href="http://k-developers.com/wp-content/uploads/2015/12/full-adder-using-NOR-logic.png"><img alt="full-adder-using-NOR-logic" class="size-full wp-image-130 aligncenter" height="279" src="http://k-developers.com/wp-content/uploads/2015/12/full-adder-using-NOR-logic.png" width="504" /></a>

Digital Design Digital Electronics Logic Gates Ripple Carry Adder

Ripple Carry AdderMultiple full adder circuits can be cascaded in parallel to add an N-bit number. For an N- bit parallel adder, there must be N number of full adder circuits. A ripple carry adder is a logic circuit in which the carry-out of each ful…

Advanced Database Concepts [PPT]

<h2>Advanced Database Concepts</h2><br/>A <b>database</b> is an organized collection of data. It is the collection of schemas, tables, queries, reports, views and other objects. The data is typically organized to model aspects of reality in a way that supports processes requiring information.<br/><br/>A <b>database management system</b> (<b>DBMS</b>) is a computer software application that interacts with the user, other applications, and the database itself to capture and analyse data. A general-purpose DBMS is designed to allow the definition, creation, querying, update, and administration of databases. Well-known DBMSs include <a title="MySQL" href="https://en.wikipedia.org/wiki/MySQL">MySQL</a>, <a title="PostgreSQL" href="https://en.wikipedia.org/wiki/PostgreSQL">PostgreSQL</a>,<a title="Microsoft SQL Server" href="https://en.wikipedia.org/wiki/Microsoft_SQL_Server">Microsoft SQL Server</a>, <a title="Oracle Database" href="https://en.wikipedia.org/wiki/Oracle_Database">Oracle</a>, <a title="Sybase" href="https://en.wikipedia.org/wiki/Sybase">Sybase</a> and <a title="IBM DB2" href="https://en.wikipedia.org/wiki/IBM_DB2">IBM DB2</a>.<br/><br/>Following are some MS Powerpoint presentations covering some advanced DBMS concepts.<br/><br/>1) <a href="http://k-developers.com/wp-content/uploads/2015/12/Transaction-Processing-Concepts.pptx">Transaction Processing Concepts</a><br/><br/>2) <a href="http://k-developers.com/wp-content/uploads/2015/12/Indexing-and-Hashing.pptx">Indexing and Hashing</a><br/><br/>3) <a href="http://k-developers.com/wp-content/uploads/2015/12/Query-Processing-and-Optimization.pptx">Query Processing and Optimization</a><br/><br/>4) <a href="http://k-developers.com/wp-content/uploads/2015/12/Storage-in-Database.ppt">Data Storage in Database</a><br/><br/>5) <a href="http://k-developers.com/wp-content/uploads/2015/12/Database-Concurrency-Control-and-Recovery.ppt">Database Concurrency Control and Recovery</a>

Database Management DBMS Indexing and Hashing Advanced Database Concepts [PPT]

Advanced Database ConceptsA database is an organized collection of data. It is the collection of schemas, tables, queries, reports, views and other objects. The data is typically organized to model aspects of reality in a way that supports processes …

Input Output organisation

<h1><span class="Apple-style-span"><strong>Accessing I/O Devices:-</strong></span></h1><br/><ul><br/>	<li>Most modern computers use single bus arrangement for connecting I/O devices to CPU & Memory.</li><br/>	<li>The bus enables all the devices connected to it to exchange information.</li><br/>	<li>Bus consists of 3 set of lines : Address, Data & Control Lines.</li><br/>	<li>Processor places a particular address (unique for an I/O Device) on address lines.</li><br/>	<li>Device which recognizes this address responds to the commands issued on the Control lines.</li><br/>	<li>Processor requests for either Read/Write.</li><br/>	<li>The data will be placed on Data lines</li><br/></ul><br/><h1><span class="Apple-style-span"><strong>I/O INTERFACE:-</strong></span><strong><a href="http://k-developers.com/wp-content/uploads/2015/12/iointerface.png"><img alt="iointerface" class="size-full wp-image-100 aligncenter" height="377" src="http://k-developers.com/wp-content/uploads/2015/12/iointerface.png" width="851" /></a></strong></h1><br/><div>1) It is a special hardware used to connect the I/O device to the bus , i.e, I/O interface.</div><br/><div>2)The I/O module has following sections:-</div><br/><ul><br/>	<li><strong>Address decoder:-</strong> It enables the device to recognize its address when this address appears on the address lines.</li><br/>	<li><strong>Data register:-</strong> The data register holds the data being transferred to or from the processor.</li><br/></ul><br/><div>3) The status register contains information relevant to the operation of the I/O module.</div><br/><div>* Both the data and status register are connected to the data bus.</div><br/><div><a href="http://k-developers.com/wp-content/uploads/2015/12/iomodule.png"><img alt="iomodule" class="size-full wp-image-101 aligncenter" height="331" src="http://k-developers.com/wp-content/uploads/2015/12/iomodule.png" width="692" /></a></div><br/><div></div><br/><h2><strong>MODES OF DATA TRANSFER:-</strong></h2><br/><div><strong>1.Programmed I/O Mode:-</strong></div><br/><div>1) In programmed I/O mode data are exchanged between the processor and the I/O module.  When a processor is executing a program and encounters an instruction relating to I/O, it executes that instruction by issuing a command to that appropriate I/O module. With programmed I/O the I/O module will perform the requested action and then set the appropriate bit in the I/O status register.</div><br/><div>2) The I/O module takes no further action to alert the processor (it doesn't interrupt the processor).</div><br/><div>3) The I/O commands issued by the processor to the I/O module</div><br/><ul><br/>	<li>Test</li><br/>	<li>Control</li><br/>	<li>Read</li><br/>	<li>Write</li><br/></ul><br/><div><strong>2.Memory Mapped I/O:-</strong></div><br/><div>1) There is a single address space for memory location and I/O devices.( the address space is shared)</div><br/><div>2) With memory mapped I/O a single read line a single write line are needed on the bus. The bus may be equipped with memory read and write plus Input and output command lines.</div><br/><div>3) Now the command lines specifies whether the address refers to memory location or an I/O device.</div><br/><div>4) Most CPU uses memory mapped I/O.</div><br/><div>5) Always CPU assigns address to memory some of memory space is stolen and assigned to I/O device.</div><br/><div>6) It deals with fewer address lines.</div><br/><div><a href="http://k-developers.com/wp-content/uploads/2015/12/MEMORYMAPED.png"><img alt="MEMORYMAPED" class="size-full wp-image-102 aligncenter" height="318" src="http://k-developers.com/wp-content/uploads/2015/12/MEMORYMAPED.png" width="709" /></a></div><br/><div></div><br/><div><strong>3.Interrupt Driven I/O:-</strong></div><br/><div>1) In this method the program issues an I/O command and than continues to execute until it is interrupted by the I/O hardware to signal the end of I/O operation.</div><br/><div>2) Here the program enters a wait loop in which it repeatedly checks the device status. During this process the processor is not performing any useful computation.</div><br/><div>3) There are many situations where tasks can be performed while waiting for an I/O device to be ready, to allow this the I/O device should alert the processor when it becomes ready. It can be done by sending a hardware signal called an <strong>interrupt.</strong></div><br/><div>4) The routine executed in response to an interrupt request is called<strong> Interrupt Service Routine </strong>(ISR).</div><br/><div>5) The processor first completes execution of instruction then it loads the program counter(pc) with the address of first instruction of ISR.</div><br/><h3><strong>4.Direct Memory Access:-</strong></h3><br/><div>1) In this method the input and output devices read/write information from the main memory without interference of the CPU through the system bus.</div><br/><div>2) For I/O transfer, processor determines the status of I/O by:</div><br/><ul><br/>	<li>Polling</li><br/>	<li>Waiting for interrupt signal.</li><br/></ul><br/><div>3) Considerable Overhead is incurred in above I/O transfer processing.</div><br/><div>4) By DMA approach , large blocks of data at high speed can be sent between external device and main memory.</div><br/><div><strong>DMA CONTROLLER:-</strong></div><br/><div>1) It allows the data transfer between I/O device and memory.</div><br/><div>2) DMA controllers acts a processor but it is controlled by the CPU. To initiate the transfer of a block of words, the processor sends the following data to controller</div><br/><ul><br/>	<li>Starting address of memory block</li><br/>	<li>The word count</li><br/>	<li>Control to specify the mode of transfer such as read or write.</li><br/>	<li>A control to start the DMA transfer.</li><br/></ul><br/><div>3) The DMA controller performs the required I/O operation and send a interrupt to the processor upon completion.</div><br/><div></div><br/><div> <a href="http://k-developers.com/wp-content/uploads/2015/12/DMA.png"><img alt="DMA" class="size-full wp-image-103 aligncenter" height="377" src="http://k-developers.com/wp-content/uploads/2015/12/DMA.png" width="662" /></a></div><br/><h2><strong><span class="Apple-style-span">Use Of DMA controller in Computer System</span></strong></h2><br/><div><span class="Apple-style-span">1) DMA device have higher priority then processor over BUS control.</span></div><br/><div>2) Types of DMA Transfer:-</div><br/><ul><br/>	<li>Cycle stealing</li><br/>	<li>Burst mode</li><br/></ul><br/><div><strong>Cycle Stealing:-</strong></div><br/><div>DMA controller ‘steals’ memory cycles from the processor though processor originates most memory access.</div><br/><div><b>Burst</b><strong> mode:- </strong></div><br/><div>The DMA controller may be given exclusive access to the main memory to transfer a block of data without interruption.</div><br/><div><strong>Conflicts Of DMA</strong>:-</div><br/><ul><br/>	<li>Conflict between processor and DMA</li><br/>	<li>Two DMA Controller try to access the BUS at same time to access the main memory.</li><br/></ul><br/><br/><hr /><br/><br/>

Computer Organisation I/O Organisation Input Output organisation

Accessing I/O Devices:- Most modern computers use single bus arrangement for connecting I/O devices to CPU & Memory. The bus enables all the devices connected to it to exchange information. Bus consists of 3 set of lines : Address, Data & Control Lin…