Learn.... Share.... Repeat....
SOME STEPS TO STAY SECURE
1. U may avoid using Internet Explorer(old versions) and make the switch to Opera, it's more secure, plain and simple.2. Get Spybot Search and Destroy or Spyware Doctor and immediately update it.3. Get Adaware SE and immediately update it.(Use both as a 1-2 punch on infected client computers and between the two there's not much they won't kill)4. Update your anti virus,5. Boot into safe mode and run all three scans (once in a month)6. While the scans are going check your registry (Click start --> Run and type regedit to get intot he registry) and look in HKEY_CurrentUser/software/microsoft/windows/currentversion/run & HKEY_Local_Machine/software/microsoft/windows/currentversion/run. Verify that all programs listed are legitimate and wanted.7. If or when your antivirus scan comes across anything, search for that file name in your registry and delete it, at least quarantine it.8. Use explorer to go to the windows/system32 folder and sort by date. If you haven't already done so, make sure you can see the entire file names. click Tools --> Folder Options and unclick the box labeled "Hide extensions for known file types" and under Hidden files and folders click "Show hidden files and folders." However, make sure you choose "Hide protected operating system files" so you don't accidentally remove anything that would cripple your computer.. You are looking for recent files with names ending with .exe and .dll that look suspicious. Major culprits will have gibberish names such as alkjdlkjfa.exe.9. Once you can get clean scans in safe mode, reboot in normal mode and scan all over again. If you can't get a clean scan in regular mode then you have something more persistant that could take more research.10. Make sure your firewall doesn't have strange exceptions.11. If you suspect anything that is going wrong with your computer is the action of a stalker, on a more secure system change all your major passwords, mostly bu using a virtual keyboard(to prevent keyloggers).12. If your system has been specifically targeted and hacked you can never be 100% sure that your system is no longer compromised so start with 11, make backups of personal files on the infected system and format and re-install Windows.
India Approves Satyam Stake Sale to Tech Mahindra
April 16 (Bloomberg) -- India’s Company Law Board approved Satyam Computer Services Ltd.’s sale of a 31 percent stake to Tech Mahindra Ltd. for 17.6 billion rupees ($355 million).
Tech Mahindra on April 13 won the bidding for control of Satyam, the software exporter at the center of India’s biggest fraud inquiry, beating U.S. billionaire Wilbur Ross and Larsen & Toubro Ltd. with a $579 million offer. The sale needed the law panel’s approval after the government took control of the company in January in the wake of its founder Ramalinga Raju’s admission that he’d inflated assets by more than $1 billion.
The approval allows Tech Mahindra to make a mandatory open offer for a 20 percent stake from shareholders and nominate its executives to Satyam’s board. Pune-based Tech Mahindra can take charge of a business serving clients including Cisco Systems Inc. and Nestle SA and almost triple its workforce, boosting its ability to compete with larger rivals Tata Consultancy Services Ltd. and Infosys Technologies Ltd.
Tech Mahindra can nominate “not more than four of its nominees” as directors on Satyam’s board, S. Balasubramanian, the law panel’s chairman, said in the order. These nominees can function “without apprehension of being subjected to civil, criminal or punitive actions” while the fraud probe is in progress. Satyam’s six state-appointed directors will also stay on until further orders, he said.
Satyam also gets time until Dec. 31 to restate its accounts, according to the order.
Set up as a venture between BT Group and India’s largest utility-vehicle maker, Mahindra & Mahindra Ltd., in 1986, Tech Mahindra counts the British telecommunications company as its largest client and mainly serves phone companies in Europe. The software exporter had 25,429 employees at the end of December, about half of Satyam’s workforce of 48,000.
Satyam fell 4.4 percent to 45.45 rupees at 2:50 p.m. in Mumbai trading, while Tech Mahindra declined 3 percent to 357.55 rupees. The benchmark Sensitive Index lost 1.3 percent.
Tech Mahindra on April 13 won the bidding for control of Satyam, the software exporter at the center of India’s biggest fraud inquiry, beating U.S. billionaire Wilbur Ross and Larsen & Toubro Ltd. with a $579 million offer. The sale needed the law panel’s approval after the government took control of the company in January in the wake of its founder Ramalinga Raju’s admission that he’d inflated assets by more than $1 billion.
The approval allows Tech Mahindra to make a mandatory open offer for a 20 percent stake from shareholders and nominate its executives to Satyam’s board. Pune-based Tech Mahindra can take charge of a business serving clients including Cisco Systems Inc. and Nestle SA and almost triple its workforce, boosting its ability to compete with larger rivals Tata Consultancy Services Ltd. and Infosys Technologies Ltd.
Tech Mahindra can nominate “not more than four of its nominees” as directors on Satyam’s board, S. Balasubramanian, the law panel’s chairman, said in the order. These nominees can function “without apprehension of being subjected to civil, criminal or punitive actions” while the fraud probe is in progress. Satyam’s six state-appointed directors will also stay on until further orders, he said.
Satyam also gets time until Dec. 31 to restate its accounts, according to the order.
Set up as a venture between BT Group and India’s largest utility-vehicle maker, Mahindra & Mahindra Ltd., in 1986, Tech Mahindra counts the British telecommunications company as its largest client and mainly serves phone companies in Europe. The software exporter had 25,429 employees at the end of December, about half of Satyam’s workforce of 48,000.
Satyam fell 4.4 percent to 45.45 rupees at 2:50 p.m. in Mumbai trading, while Tech Mahindra declined 3 percent to 357.55 rupees. The benchmark Sensitive Index lost 1.3 percent.
HACKING HISTORY
Nowadays, different people have different views on the hacking scene. Often times people of similar skill level have similar opinions. There is no official definition of a hacker, rather a vague idea amongst the masses. In addition, the media loves to add false information to draw audiences' attention across the nation, for the pure sake of money.It all began in the 1960s at MIT, origin of the term "hacker", where extremely skilled individuals practiced hardcore programming in FORTRAN and other older languages. Some may ignorantly dub them "nerds" or "geeks" but these individuals were, by far, the most intelligent, individual, and intellectually advanced people who happen to be the pioneers and forefathers of the talented individuals that are today the true hackers. The true hackers amongst our societies have an unquenchable thirst for knowledge. Boredom is never an object of challenge for hackers. They have an almost anomalous ability to absorb, retain, and exert vast amounts of knowledge with regard to intricate details. In 1969, Bell Labs employee Ken Thompson invented UNIX and permanently changed the future of the computer industry. Then in the very early 1970s, Dennis Ritchie invented the computer programming language "C" which was specifically invented to be used with UNIX. Programmers ceased to use assembler, while developing an appreciation for the portability of "C."Hackers used to be viewed as people who sat locked in a room all day programming nonstop, hours on end. No one seemed to mind hackers back in the 1960s when this was the most widely excepted reputation. In fact, most people had no idea what hacking was. The term hacker was accepted as a positive label slapped onto computer gurus who could push computer systems beyond the defined limits. Hackers emerged out of the artificial intelligence labs at MIT in the 1960s. A network known as ARPANET was founded by the Department of Defense as a means to link government offices. In time, ARPANET evolved into what is today known as the Internet.In the 1970s, "Captain Crunch" devised a way to make free long distance calls and groups of phone hackers, later dubbed "phreakers" emerged. Throughout the 1970s and halfway into the 1980s, XEROX's Palo Alto Research Center (PARC) spit out fresh new innovations such as the laser printer and LANs.During the early 1980s, the term "cyberspace" is coined from a novel called "Neuromancer." A group called the "414s" is one of the earliest hacker groups to ever get raided by the FBI and they get charged with 60 computer intrusions. Usenets began to pop up around the nation at this time and hackers exchanged thoughts using their UNIX based machines. While all of this was going on, the Secret Service was granted jurisdiction over credit card and computer fraud. During the 1980s, hacking was not known amongst the masses as it is presently. To be a hacker was to be a part of a very exclusive and secluded group. The infamous hacker groups the "Legion of Doom," based in the USA and the "Chaos Computer Club," based in Germany, were founded and are still two of the most widely recognized and respected hacker groups ever founded. Another significant foundation is that of "2600: The Hacker Quarterly," an old school hacker magazine or "zine." 2600 Magazine still continues to play a role in today's hacker community. As the end of the decade approached, Kevin Mitnick was arrested and sentenced to a year in prison on convictions of stealing software and damaging computers. In addition, federal officials raided Atlanta, where some members of the Legion of Doom were residing, at the time. The LOD, CCC, and 2600 Magazine have become known as old school hackers and are still widely respected and recognized.During the 1990s, Kevin Mitnick is arrested after being tracked down by Tsutomu Shimomura. The trials of Kevin Mitnick were of the most publicized hacker trials in hacker history.As hackers and time progressed, hackers found ways to exploit holes in operating systems of local and remote machines.Hackers have developed methods to exploit security holes in various computer systems. As protocols become updated, hackers probe them on a neverending mission to make computing more secure. In fact, due to the tendency hackers have of exploiting society, there have been spinoff categories such as "cracking" which deals with cracking software, "phreaking" which deals with exploiting phone systems, and "social engineering" which is the practice of exploiting human resources. When hacking first originated, the urge to hack into computer systems was based purely on curiosity. Curiosity of what the system did, how the system could be used, HOW the system did what did, and WHY it did what it did.Some modern day hackers archive exploit upon exploit on their machines, but archiving and using exploits is definitely not what modern hackers do. All too often, media figures and the general public mistake those who deface webpages, steal credit card numbers and/or money, and otherwise constantly wreak havoc upon the masses as hackers. You must be thinking, "Well, isn't that what hackers DO? They gain unauthorized access to computers," and technically you would be correct.HOWEVER, that's not all they do. Hackers find and release the vulnerabilities in computer systems which, if not found, could remain secret and one day lead to the downfall of our increasingly computer dependant civilization. In a way, hackers are the regulators of electronic communication. Hackers come up with useful new computer systems and solutions to make life easier for all of humanity. Whether you know it or not, I know from personal experience that ANYBODY you know could very well lead an unexposed life as a hacker. Hackers live amongst us all. They work in all of our major corporations, as well as in many small companies. Some choose to use their skills and help our government, others choose to use their skills in a more malicious and negative way. If you look around you, ANY INDIVIDUAL you see is a potential hacker. Often, it's the people who you would suspect the least that are the hackers in our society.People in our modern day society tend to stereotype hackers as well. All hackers aren't 31337lbs, 5'5, wearing glasses and suspenders, scrawny, pale skinned, with a comical Steve Urkel resemblance and no social life. If you think this, you are WRONG. Hackers are black, white, asian, european, tall, short, socially active (and not), cool, nerdy, and a bunch of other miscellaneous categories. Just like you can't make an assumption that if someone is from "Clique X" than they must be really [whatever], you can't apply a stereotype to genres of hackers. Although there are people running around saying, "Look, I defaced a website, I did it, and therefore I'm a hacker," doesn't mean that they're a hacker. Nevertheless, nor does it mean that ALL people claiming to be hackers are fakes and wannabes. It's the same in the digital underground as it is with any other realm of society.Currently, we see the commercialization of hacking. If you were to take a trip to a respectable bookstore with a good selection of books, you would find books with flat out hacking techniques. Whether these techniques can truly be classified as hacking by the classic definition of hacking is debatable. They claim to teach you hacking methods, how to become a hacker, and supposedly reveal hacker tricks to the common man.Another common misconception is that people who distribute and deal with illegal software, which is commonly known as "warez" are hackers. "Warez kings," as they are commonly known, are not necessarily hackers, however that doesn't mean that they are NOT hackers. You cannot determine the intellectual content of people by what they say or have. Moreover, hackers are not people who go around using programs in Windows such as "WinNuke" and various ICMP bombers and other miscellaneous Denial of Service programs designed to crash remote party's machines. Hackers don't distribute remote administration tools and use them as trojan horse viruses to wreak havoc on the general public and make other people's lives miserable. Real hackers want to know as much as they can and are more helpful than wreckless. While it is true that there ARE hackers that DO commit malicious acts against users, they are not to be used as a model of the norm of hackers.
Book Tata Nano Car online
Book Tata Nano Car online
Tata Nano booking is started online. You can book a Tata Nano car by filling an online booking form which costs Rs.200. But it is not refundable. Credits and Debit cards will not be accepted for online payment. Cost of application form and booking amount will have to be paid through net banking for the online booking process. Tata authorized 28 banks for Booking through net banking which are listed on Tata Nano website. Booking open from 9th April 2009 to 25th April 2009.
Tata Nano booking is started online. You can book a Tata Nano car by filling an online booking form which costs Rs.200. But it is not refundable. Credits and Debit cards will not be accepted for online payment. Cost of application form and booking amount will have to be paid through net banking for the online booking process. Tata authorized 28 banks for Booking through net banking which are listed on Tata Nano website. Booking open from 9th April 2009 to 25th April 2009.
How to promote your blog?
How to promote your blog?
Social NetworkingAre you familiar with Orkut like social networking websites? You can use these websites to promote you blog. You just add your blog address(URL) on your profile page. Your friends and new guests will click on this link and visit your blog too.If you are serious in blogging, you must build a big friendship group. TOP TEN SOCIAL NETWORKING WEBSITES IN INDIA1. Orkut 2. Facebook 3. Bharatstudent4. hi5 5. ibibo6. Myspace7. LinkedIn8. PerfSpot9. BigAdda10.Fropper
Social NetworkingAre you familiar with Orkut like social networking websites? You can use these websites to promote you blog. You just add your blog address(URL) on your profile page. Your friends and new guests will click on this link and visit your blog too.If you are serious in blogging, you must build a big friendship group. TOP TEN SOCIAL NETWORKING WEBSITES IN INDIA1. Orkut 2. Facebook 3. Bharatstudent4. hi5 5. ibibo6. Myspace7. LinkedIn8. PerfSpot9. BigAdda10.Fropper
Fastest Streaming bollywood Music Online
Fastest Streaming bollywood Music Online
Whenever a music album released in India, it's piracy version goes online. Youngsters are very intended to download these kind of piracy music, most of them in mp3 or real format. But the dangerous thing behind this illegal act is that Virus and malicious software are spreading trough the downloading. It will harm your computer. So that I prefer in.com to listen music. It is fast and legal. You will not face hassles of downloading the streaming music. It is from my personal experience. Can you say any better online music website for bollywood music?
Whenever a music album released in India, it's piracy version goes online. Youngsters are very intended to download these kind of piracy music, most of them in mp3 or real format. But the dangerous thing behind this illegal act is that Virus and malicious software are spreading trough the downloading. It will harm your computer. So that I prefer in.com to listen music. It is fast and legal. You will not face hassles of downloading the streaming music. It is from my personal experience. Can you say any better online music website for bollywood music?
How to download YouTube video in mobilephone video format
How to download YouTube video in mobilephone video format
Do you know how to download YouTube videos and convert into a mobilephone video format? Here is a simple way to download a Youtube video and convert into a 3gp or MP4 without using gprs.HOW TO1. Copy the URL of the YouTube you want to download.2. Go to Mediaconverter.org 3. Click on ENTER A LINK button in conversion wizard.4. Paste the YouTube url there.5. Click on OK button6. Click on GO TO THE NEXT BUTTON7. Select an output file (3gp or mp4 for mobilevideo format)8. Click OK 9. Click START and keep wait to download the file10. After downloading transfer the file to your mobilephone.
Do you know how to download YouTube videos and convert into a mobilephone video format? Here is a simple way to download a Youtube video and convert into a 3gp or MP4 without using gprs.HOW TO1. Copy the URL of the YouTube you want to download.2. Go to Mediaconverter.org 3. Click on ENTER A LINK button in conversion wizard.4. Paste the YouTube url there.5. Click on OK button6. Click on GO TO THE NEXT BUTTON7. Select an output file (3gp or mp4 for mobilevideo format)8. Click OK 9. Click START and keep wait to download the file10. After downloading transfer the file to your mobilephone.
Nokia Launches E75 in India
Nokia Launches E75 in India
Nokia launches its latest E-Series handset E75 in India. Nokia E75 will be available for Rs. 26, 299 in two colours - silver black and red.
Nokia E75 Key Features Form: Side slider with Full QWERTY keyboard S60 3rd Edition Dimensions: 111.8 x 50/80 x 14.4 mm Weight: 139 g Full keyboard + number keys High quality QVGA display Size: 2.4" Resolution: 320 x 240 pixels (QVGA) TFT active matrix (QVGA) Easy email set-up and Support for email attachments 3.2 megapixel camera (2048 x 1536 pixels) 8X digital zoom Autofocus LED flash Integrated A-GPS
Nokia launches its latest E-Series handset E75 in India. Nokia E75 will be available for Rs. 26, 299 in two colours - silver black and red.
Nokia E75 Key Features Form: Side slider with Full QWERTY keyboard S60 3rd Edition Dimensions: 111.8 x 50/80 x 14.4 mm Weight: 139 g Full keyboard + number keys High quality QVGA display Size: 2.4" Resolution: 320 x 240 pixels (QVGA) TFT active matrix (QVGA) Easy email set-up and Support for email attachments 3.2 megapixel camera (2048 x 1536 pixels) 8X digital zoom Autofocus LED flash Integrated A-GPS
magazines
Go to the link to get a varity of magzines to make ur self chill out..
http://www.area51warez.info/magazines/15684-3dcreative-magazine-issue-038-october-08.html
COMPUTERS WHAT ARE THEY ????
A general purpose computer has four main components: the arithmetic and logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by busses, often made of groups of wires.
The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these) are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.
Control unit
Main articles: CPU design and Control unit
The control unit (often called a control system or central controller) manages the computer's various components; it reads and interprets (decodes) the program instructions, transforming them into a series of control signals which activate other parts of the computer.[19] Control systems in advanced computers may change the order of some instructions so as to improve performance.
A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from.[20]
Diagram showing how a particular MIPS architecture instruction would be decoded by the control system.
The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:
Read the code for the next instruction from the cell indicated by the program counter.
Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
Increment the program counter so it points to the next instruction.
Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
Provide the necessary data to an ALU or register.
If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
Write the result from the ALU back to a memory location or to a register or perhaps an output device.
Jump back to step (1).
Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. Instructions that modify the program counter are often known as "jumps" and allow for loops (instructions that are repeated by the computer) and often conditional instruction execution (both examples of control flow).
It is noticeable that the sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program—and indeed, in some more complex CPU designs, there is another yet smaller computer called a microsequencer that runs a microcode program that causes all of these events to happen.
Arithmetic/logic unit (ALU)
Main article: Arithmetic logic unit
The ALU is capable of performing two classes of operations: arithmetic and logic.[21]
The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc) and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers—albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?").
Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing boolean logic.
Superscalar computers may contain multiple ALUs so that they can process several instructions at the same time.[22] Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices.
Memory
Main article: Computer storage
Magnetic core memory was the computer memory of choice throughout the 1960s, until it was replaced by semiconductor memory.
A computer's memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered "address" and can store a single number. The computer can be instructed to "put the number 123 into the cell numbered 1357" or to "add the number that is in cell 1357 to the number that is in cell 2468 and put the answer into cell 1595". The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. Since the CPU does not differentiate between different types of information, it is the software's responsibility to give significance to what the memory sees as nothing but a series of numbers.
In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers (2^8 = 256); either from 0 to 255 or -128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two's complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory if it can be represented numerically. Modern computers have billions or even trillions of bytes of memory.
The CPU contains a special set of memory cells called registers that can be read and written to much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. As data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer's speed.
Computer main memory comes in two principal varieties: random access memory or RAM and read-only memory or ROM. RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM are erased when the power to the computer is turned off, but ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the required software may be stored in ROM. Software stored in ROM is often called firmware, because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. It is typically much slower than conventional ROM and RAM however, so its use is restricted to applications where high speed is unnecessary.[23]
In more sophisticated computers there may be one or more RAM cache memories which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.
Input/output (I/O)
Main article: Input/output
Hard disks are common I/O devices used with computers.
I/O is the means by which a computer exchanges information with the outside world.[24] Devices that provide input or output to the computer are called peripherals.[25] On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O.
Often, I/O devices are complex computers in their own right with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics[citation needed]. Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O.
Multitasking
Main article: Computer multitasking
While a computer may be viewed as running one gigantic program stored in its main memory, in some systems it is necessary to give the appearance of running several programs simultaneously. This is achieved by multitasking i.e. having the computer switch rapidly between running each program in turn.[26]
One means by which this is done is with a special signal called an interrupt which can periodically cause the computer to stop executing instructions where it was and do something else instead. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running "at the same time", then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time even though only one is ever executing in any given instant. This method of multitasking is sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn.[27]
Before the era of cheap computers, the principle use for multitasking was to allow many people to share the same computer.
Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly - in direct proportion to the number of programs it is running. However, most programs spend much of their time waiting for slow input/output devices to complete their tasks. If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a "time slice" until the event it is waiting for has occurred. This frees up time for other programs to execute so that many programs may be run at the same time without unacceptable speed loss.
Multiprocessing
Main article: Multiprocessing
Cray designed many supercomputers that used multiprocessing heavily.
Some computers are designed to distribute their work across several CPUs in a multiprocessing configuration, a technique once employed only in large and powerful machines such as supercomputers, mainframe computers and servers. Multiprocessor and multi-core (multiple CPUs on a single integrated circuit) personal and laptop computers are now widely available, and are being increasingly used in lower-end markets as a result.
Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers.[28] They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful only for specialized tasks due to the large scale of program organization required to successfully utilize most of the available resources at once. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel" tasks.
Networking and the Internet
Main articles: Computer networking and Internet
Visualization of a portion of the routes on the Internet.
Computers have been used to coordinate information between multiple locations since the 1950s. The U.S. military's SAGE system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems like Sabre.[29]
In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. This effort was funded by ARPA (now DARPA), and the computer network that it produced was called the ARPANET.[30] The technologies that made the Arpanet possible spread and evolved.
In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become almost ubiquitous. In fact, the number of computers that are networked is growing phenomenally. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. "Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments.
The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these) are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.
Control unit
Main articles: CPU design and Control unit
The control unit (often called a control system or central controller) manages the computer's various components; it reads and interprets (decodes) the program instructions, transforming them into a series of control signals which activate other parts of the computer.[19] Control systems in advanced computers may change the order of some instructions so as to improve performance.
A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from.[20]
Diagram showing how a particular MIPS architecture instruction would be decoded by the control system.
The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:
Read the code for the next instruction from the cell indicated by the program counter.
Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.
Increment the program counter so it points to the next instruction.
Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.
Provide the necessary data to an ALU or register.
If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.
Write the result from the ALU back to a memory location or to a register or perhaps an output device.
Jump back to step (1).
Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. Instructions that modify the program counter are often known as "jumps" and allow for loops (instructions that are repeated by the computer) and often conditional instruction execution (both examples of control flow).
It is noticeable that the sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program—and indeed, in some more complex CPU designs, there is another yet smaller computer called a microsequencer that runs a microcode program that causes all of these events to happen.
Arithmetic/logic unit (ALU)
Main article: Arithmetic logic unit
The ALU is capable of performing two classes of operations: arithmetic and logic.[21]
The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc) and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers—albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?").
Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing boolean logic.
Superscalar computers may contain multiple ALUs so that they can process several instructions at the same time.[22] Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices.
Memory
Main article: Computer storage
Magnetic core memory was the computer memory of choice throughout the 1960s, until it was replaced by semiconductor memory.
A computer's memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered "address" and can store a single number. The computer can be instructed to "put the number 123 into the cell numbered 1357" or to "add the number that is in cell 1357 to the number that is in cell 2468 and put the answer into cell 1595". The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. Since the CPU does not differentiate between different types of information, it is the software's responsibility to give significance to what the memory sees as nothing but a series of numbers.
In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers (2^8 = 256); either from 0 to 255 or -128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two's complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory if it can be represented numerically. Modern computers have billions or even trillions of bytes of memory.
The CPU contains a special set of memory cells called registers that can be read and written to much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. As data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer's speed.
Computer main memory comes in two principal varieties: random access memory or RAM and read-only memory or ROM. RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM are erased when the power to the computer is turned off, but ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the required software may be stored in ROM. Software stored in ROM is often called firmware, because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. It is typically much slower than conventional ROM and RAM however, so its use is restricted to applications where high speed is unnecessary.[23]
In more sophisticated computers there may be one or more RAM cache memories which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.
Input/output (I/O)
Main article: Input/output
Hard disks are common I/O devices used with computers.
I/O is the means by which a computer exchanges information with the outside world.[24] Devices that provide input or output to the computer are called peripherals.[25] On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O.
Often, I/O devices are complex computers in their own right with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics[citation needed]. Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O.
Multitasking
Main article: Computer multitasking
While a computer may be viewed as running one gigantic program stored in its main memory, in some systems it is necessary to give the appearance of running several programs simultaneously. This is achieved by multitasking i.e. having the computer switch rapidly between running each program in turn.[26]
One means by which this is done is with a special signal called an interrupt which can periodically cause the computer to stop executing instructions where it was and do something else instead. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running "at the same time", then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time even though only one is ever executing in any given instant. This method of multitasking is sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn.[27]
Before the era of cheap computers, the principle use for multitasking was to allow many people to share the same computer.
Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly - in direct proportion to the number of programs it is running. However, most programs spend much of their time waiting for slow input/output devices to complete their tasks. If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a "time slice" until the event it is waiting for has occurred. This frees up time for other programs to execute so that many programs may be run at the same time without unacceptable speed loss.
Multiprocessing
Main article: Multiprocessing
Cray designed many supercomputers that used multiprocessing heavily.
Some computers are designed to distribute their work across several CPUs in a multiprocessing configuration, a technique once employed only in large and powerful machines such as supercomputers, mainframe computers and servers. Multiprocessor and multi-core (multiple CPUs on a single integrated circuit) personal and laptop computers are now widely available, and are being increasingly used in lower-end markets as a result.
Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers.[28] They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful only for specialized tasks due to the large scale of program organization required to successfully utilize most of the available resources at once. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel" tasks.
Networking and the Internet
Main articles: Computer networking and Internet
Visualization of a portion of the routes on the Internet.
Computers have been used to coordinate information between multiple locations since the 1950s. The U.S. military's SAGE system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems like Sabre.[29]
In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. This effort was funded by ARPA (now DARPA), and the computer network that it produced was called the ARPANET.[30] The technologies that made the Arpanet possible spread and evolved.
In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become almost ubiquitous. In fact, the number of computers that are networked is growing phenomenally. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. "Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments.
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