Notes on Computer Networks v 3. Network layer Climbing up one level above data link layer is the network (or internet) layer. This layer conveys a.
Introduction of Internet Hindi Notes • 1. Only Introduction of Internet & Websites rock_siraj@ymail.com Page 1 • Only Introduction of Internet & Websites rock_siraj@ymail.com Page 2 Internet Internet inter connection network network, computers (resource) Internet internet networks network USNL/BSNL Power Outlet Server PC TL 2qure cable Client PC Switch Client PC Internet Terminology:- 1.
MODEM:- (Modulate or Demodulate) Modem devise computer data telephone line computer information digital store information telephone line analog modem 2. Network:- Network computer information share 3. Client:- Client computer program computer program I S P Modem LAB 1 LAB 2 PC • Only Introduction of Internet & Websites rock_siraj@ymail.com Page 3 4. Server:- Server computer program computer 5. Internet Service Provider:- Internet Service Provider ISP ISP company user internet 6.
Baud rat:- Baud rat modem speed data transfer signal or pluses computer one second Baud rat modem 7. TCP/IP:- Transmission Control Protocol/Internet Protocol protocols network computer network computer Protocol computer follow 8. HTTP://:- Hypertext transfer protocol protocol web server web client HTTP 9.
URL:- Uniform Resource Locater www internet web address or internet address 10. IP Address:- internet Protocol Address IP address unique numeric network computer specify IP address octs period 192. Octs.4 0 to 255 IP Address – 192.168.1.10 Subnet maze – 255.255.255.0 Default Laneway – 192.168.1.1 TCP/IP.4 – IP Class Class A – 10.0.0.0 Class B – 127.0.0.0 Class C – 192.0.0.0 11. Domain Name:- Domain Name internet computer Domain Name A Second unique internet organization domain name Domain name two type URL – http: - Web Server Address • Only Introduction of Internet & Websites rock_siraj@ymail.com Page 4 www – Host Name JCS – Server Name Com – Organization Name www.jcs.com – FQDN (Fully Qualified Domain Name) i. Organizational Domain:-.Com - Commercial Organization.edu - Educational Organization.gov - Nonmilitary government Organization.int - International Organization.mil - Military Organization.net - Network Service Provider Organization.org - Non legal Profit Organization.info - Any Users.museum - Museum Organization ii. Geographical Domain:-.au - Australia.ch - Switzerland.ge - Germany.dk - Denmark.fr - France.in - India.jp - Japan.pl - Poland.pk - Pakistan.us - United State Domain name System ICANN (Internet Corporation for Assigned name & Number) Domain name.aero.coop.home.pro Network:- computer geographical area according basically network three type distributes LAN – 0 to 1km MAN – 1km to 100km • Only Introduction of Internet & Websites rock_siraj@ymail.com Page 5 WAM – more than 100km 1. LAN (Local Area Network):- network use office building computer network use 1km 2.
MAN (Metro Politian Area Network):- 1km to 100km branches MAN use 3. WAN (Wide Area Network):- worldwide country or District computer country District or Village computer information receive Network Topologies:- computer connection layout topologies Eg. Start Topologies Ring Topologies Bus Topologies Hybrid Topologies Mass Topologies Type of Internet Communication:- Internet 1. E-mail in short massaging 2. Social networking 3.
Block & Quiz Spam Blockers:- Stand massaging Services:- 1. Red if boll instant messenger 2. MSN Messenger 3.
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Www.twiter.com 7. Www.linkdin.com 8. Www.meetup.com www.wikipedia:- online Topic Related information upload read Search Engine:- 1. Www.ask.com 2.
Www.google.com 3. Www.MSN.com 4. Www.yahoo.com 5. Www.excite.com 6. Www.rediff.com 7. Www.altavista.com 8. Www.infoseek.com 9.
Www.lyfoseek.com 10. Www.webcrawler.com 11. Www.mckinley.com 12. Www.galaxy.com Mata Search Engine:- 1. Www.hindustan.net 2. Www.indiabook.com 3. Www.khoj.com Special Search Engine:- • Only Introduction of Internet & Websites rock_siraj@ymail.com Page 7 1.
Www.eco-web.com Environment 2. Www.infomat.com Faction 3. Www.historynet.com History 4. Www.lowcrawler.com Law 5. Www.medsite.com Law Electronic Commerce:- 1. Www.shopping.com Comparison of Product 2. Www.overstock.com Search of Places 3.
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Www.auctions.overstock.com Electronic Cash Providers:- 1. Www.ecash.com E-Cash 2. Www.checkout.google.com Google 3. Www.internetcash.com Internet Cash 4.
Www.paypal.com PayPal Audio Songs:- 1. Www.Songspk.com 2. Www.pksongs.com Video Songs:- 1. Www.freshmaza.com 2. Www.youtube.com Movies:- 1. Www.fzmovies.com 2.
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Www.clipart.com 3. Www.graphicofactory.com 4.
Www.officemicrosoft.com/clipart 5. Www.istockphoto.com 6. Www.flicker.com/creatinecommns • Only Introduction of Internet & Websites rock_siraj@ymail.com Page 9 Main E-mails Program:- 1. Ms-outlook express 2. Www.gmail.com 3.
Www.yahoomail.com 4. Www.rediffmail.com 5. Www.hotmail.com 6. Www.loutsmail.com 7. Www.linemail.com Basic Requirement of the Outlook Configuration:- 1. Incoming mail server. Outgoing mail server.
SMTP,IMAP,HTTP POP3 = Post Office Protocol Version 3 SMTP = Simple Mail Transfer Protocol IMAP = Internet Mail Access Protocol HTTP = Hyper Text Transfer Protocol Web utilities Software:- 1. E-mail:- E-mail massage application help computer computer transfer 2. G-mail:- G-mail E-mail service provider massage (E-mail) computer computer transfer help E-mail Client:- 1. Outlook Express 2. Outlook Live 3. Windows Mail 4.
Yahoo Mail 6. Rediff Mail 8. Thunder Bird 9. Apps Live.etc.
Application Service Provider (ISP) File Transfer Protocol (FTP) • Only Introduction of Internet & Websites rock_siraj@ymail.com Page 10 Secured File Transfer Protocol (SFTP) Plugs in Sites:- 1. Adobe Acrobat:- PDF format save form print 2. Windows Media Player from Microsoft:- Audio files, video files files play 3. Apples a Quick Time:- Audio files, video files files play 4. Real Player of Real Networks:- Audio files, video files files play 5. Adobe a Soft view:- Web games play animation 6.
Win naps:- Audio files, video files files play 7. VLC Media Player from VLC:- Audio files, video files files play Players Software:- 1. Www.adobe.com 2. Www.microsoft.com 3.
Www.apple.com 4. Www.service.real.com 5. Www.winnapsplayer.com 6. Www.VLCmediaplayer.com Software:- 1. Www.Client.com 2. Www.cnet.com 3. Www.microsoft.com Video Calling Software:- 1.
Www.skype.com Scripting Language’s Programs:- 1. Www.school.com (Microsoft Development Environment [Design] Downloading:- other server file computer Downloading • Only Introduction of Internet & Websites rock_siraj@ymail.com Page 11 Uploading:- computer file, Photo, Audio, Video network server Uploading YouTube Direct Video Download Steps Follow 1. URL web server YouTube ss enter press download link (Save Net Helper and Java Script) Install 2.
YouTube Download Software YouTube Download manager Install Adobe a Flash Player (Software):- YouTube Video Player Adobe Flash Player Version Install Image Viewer Software Image viewer Picasa Online Shopping = Use in Google.
Computers and computing devices from different eras A computer is a device that can be to carry out arbitrary sequences of or operations automatically. The ability of computers to follow generalized sets of operations, called, enables them to perform an extremely wide range of tasks. Such computers are used as for a very wide variety of and. This includes simple special purpose devices like and, factory devices such as and, but also in general purpose devices like and such as. The is run on computers and it connects millions of other computers.
Since ancient times, simple manual devices like the aided people in doing calculations. Early in the, some mechanical devices were built to automate long tedious tasks, such as guiding patterns for. More sophisticated electrical did specialized calculations in the early 20th century. The first electronic calculating machines were developed during.
The speed, power, and versatility of computers has increased continuously and dramatically since then. Conventionally, a modern computer consists of at least one, typically a (CPU), and some form of. The processing element carries out arithmetic and logical operations, and a sequencing and control unit can change the order of operations in response to stored.
Devices include input devices (keyboards, mice, joystick, etc.), output devices (monitor screens, printers, etc.), and input/output devices that perform both functions (e.g., the 2000s-era ). Peripheral devices allow information to be retrieved from an external source and they enable the result of operations to be saved and retrieved. Contents • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Etymology According to the Oxford English Dictionary, the first known use of the word 'computer' was in 1613 in a book called The Yong Mans Gleanings by English writer Richard Braithwait: 'I haue [sic] read the truest computer of Times, and the best Arithmetician that euer [sic] breathed, and he reduceth thy dayes into a short number.'
This usage of the term referred to a person who carried out calculations or computations. The word continued with the same meaning until the middle of the 20th century. From the end of the 19th century the word began to take on its more familiar meaning, a machine that carries out computations.
The Online Etymology Dictionary gives the first attested use of 'computer' in the '1640s, [meaning] 'one who calculates,'; this is an '. agent noun from compute (v.)'. The Online Etymology Dictionary states that the use of the term to mean 'calculating machine' (of any type) is from 1897.' The Online Etymology Dictionary indicates that the 'modern use' of the term, to mean 'programmable digital electronic computer' dates from '. 1945 under this name; [in a] theoretical [sense] from 1937, as '. The -designed, dating between 150 and 100 BC, is the world's oldest analog computer.
The is believed to be the earliest mechanical analog 'computer', according to. It was designed to calculate astronomical positions. It was discovered in 1901 in the off the Greek island of, between and, and has been dated to circa 100 BC. Devices of a level of complexity comparable to that of the Antikythera mechanism would not reappear until a thousand years later. Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use. The was a invented by Abū Rayhān al-Bīrūnī in the early 11th century.
The was invented in the in either the 1st or 2nd centuries BC and is often attributed to. A combination of the planisphere and, the astrolabe was effectively an analog computer capable of working out several different kinds of problems in. An astrolabe incorporating a mechanical computer and -wheels was invented by Abi Bakr of, in 1235. Invented the first mechanical geared astrolabe, an early fixed- knowledge processing with a and gear-wheels, circa 1000 AD. The, a calculating instrument used for solving problems in proportion, trigonometry, multiplication and division, and for various functions, such as squares and cube roots, was developed in the late 16th century and found application in gunnery, surveying and navigation. The was a manual instrument to calculate the area of a closed figure by tracing over it with a mechanical linkage.
A portion of., an English mechanical engineer and, originated the concept of a programmable computer. Considered the ', he conceptualized and invented the first in the early 19th century. After working on his revolutionary, designed to aid in navigational calculations, in 1833 he realized that a much more general design, an, was possible. Donizetti Concertino Pdf Download.
The input of programs and data was to be provided to the machine via, a method being used at the time to direct mechanical such as the. For output, the machine would have a printer, a curve plotter and a bell. The machine would also be able to punch numbers onto cards to be read in later. The Engine incorporated an, in the form of and, and integrated, making it the first design for a general-purpose computer that could be described in modern terms as. The machine was about a century ahead of its time. All the parts for his machine had to be made by hand — this was a major problem for a device with thousands of parts. Eventually, the project was dissolved with the decision of the to cease funding.
Babbage's failure to complete the analytical engine can be chiefly attributed to difficulties not only of politics and financing, but also to his desire to develop an increasingly sophisticated computer and to move ahead faster than anyone else could follow. Nevertheless, his son, Henry Babbage, completed a simplified version of the analytical engine's computing unit (the mill) in 1888. He gave a successful demonstration of its use in computing tables in 1906. Analog computers.
's third tide-predicting machine design, 1879–81 During the first half of the 20th century, many scientific needs were met by increasingly sophisticated, which used a direct mechanical or electrical model of the problem as a basis for. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers. The first modern analog computer was a, invented by in 1872.
The, a mechanical analog computer designed to solve differential equations by integration using wheel-and-disc mechanisms, was conceptualized in 1876 by, the brother of the more famous Lord Kelvin. The art of mechanical analog computing reached its zenith with the, built by H. Hazen and at starting in 1927. This built on the mechanical integrators of and the torque amplifiers invented by H. A dozen of these devices were built before their obsolescence became obvious. By the 1950s the success of digital electronic computers had spelled the end for most analog computing machines, but analog computers remained in use during the 1950s in some specialized applications such as education () and aircraft (). Digital computers.
Replica of 's, the first fully automatic, digital (electromechanical) computer. Early digital computers were electromechanical; electric switches drove mechanical relays to perform the calculation.
These devices had a low operating speed and were eventually superseded by much faster all-electric computers, originally using. The, created by German engineer in 1939, was one of the earliest examples of an electromechanical relay computer. In 1941, Zuse followed his earlier machine up with the, the world's first working, fully automatic digital computer. The Z3 was built with 2000, implementing a 22 that operated at a of about 5–10. Program code was supplied on punched while data could be stored in 64 words of memory or supplied from the keyboard.
It was quite similar to modern machines in some respects, pioneering numerous advances such as. Rather than the harder-to-implement decimal system (used in 's earlier design), using a system meant that Zuse's machines were easier to build and potentially more reliable, given the technologies available at that time.
Vacuum tubes and digital electronic circuits Purely elements soon replaced their mechanical and electromechanical equivalents, at the same time that digital calculation replaced analog. The engineer, working at the in in the 1930s, began to explore the possible use of electronics for the. Experimental equipment that he built in 1934 went into operation five years later, converting a portion of the network into an electronic data processing system, using thousands of. In the US, and of Iowa State University developed and tested the (ABC) in 1942, the first 'automatic electronic digital computer'.
This design was also all-electronic and used about 300 vacuum tubes, with capacitors fixed in a mechanically rotating drum for memory. Was the first computing device, and was used to break German ciphers during World War II. During World War II, the British at achieved a number of successes at breaking encrypted German military communications. The German encryption machine,, was first attacked with the help of the electro-mechanical.
To crack the more sophisticated German machine, used for high-level Army communications, and his colleagues commissioned Flowers to build the. He spent eleven months from early February 1943 designing and building the first Colossus. After a functional test in December 1943, Colossus was shipped to Bletchley Park, where it was delivered on 18 January 1944 and attacked its first message on 5 February. Colossus was the world's first computer. It used a large number of valves (vacuum tubes). It had paper-tape input and was capable of being configured to perform a variety of operations on its data, but it was not.
Nine Mk II Colossi were built (The Mk I was converted to a Mk II making ten machines in total). Colossus Mark I contained 1,500 thermionic valves (tubes), but Mark II with 2,400 valves, was both 5 times faster and simpler to operate than Mark I, greatly speeding the decoding process. Was the first electronic, Turing-complete device, and performed ballistics trajectory calculations for the. The U.S.-built (Electronic Numerical Integrator and Computer) was the first electronic programmable computer built in the US. Although the ENIAC was similar to the Colossus, it was much faster, more flexible, and it was. Like the Colossus, a 'program' on the ENIAC was defined by the states of its patch cables and switches, a far cry from the electronic machines that came later.
Once a program was written, it had to be mechanically set into the machine with manual resetting of plugs and switches. It combined the high speed of electronics with the ability to be programmed for many complex problems. It could add or subtract 5000 times a second, a thousand times faster than any other machine. It also had modules to multiply, divide, and square root. High speed memory was limited to 20 words (about 80 bytes). Built under the direction of and at the University of Pennsylvania, ENIAC's development and construction lasted from 1943 to full operation at the end of 1945. The machine was huge, weighing 30 tons, using 200 kilowatts of electric power and contained over 18,000 vacuum tubes, 1,500 relays, and hundreds of thousands of resistors, capacitors, and inductors.
Modern computers Concept of modern computer The principle of the modern computer was proposed by in his seminal 1936 paper, On Computable Numbers. Turing proposed a simple device that he called 'Universal Computing machine' and that is now known as a. He proved that such a machine is capable of computing anything that is computable by executing instructions (program) stored on tape, allowing the machine to be programmable.
The fundamental concept of Turing's design is the, where all the instructions for computing are stored in memory. Acknowledged that the central concept of the modern computer was due to this paper. Turing machines are to this day a central object of study in. Except for the limitations imposed by their finite memory stores, modern computers are said to be, which is to say, they have execution capability equivalent to a universal Turing machine. Stored programs.
A section of the, the first stored-program computer. Early computing machines had fixed programs. Changing its function required the re-wiring and re-structuring of the machine. With the proposal of the stored-program computer this changed. A stored-program computer includes by design an and can store in memory a set of instructions (a ) that details the.
The theoretical basis for the stored-program computer was laid by in his 1936 paper. In 1945 Turing joined the and began work on developing an electronic stored-program digital computer. His 1945 report 'Proposed Electronic Calculator' was the first specification for such a device. John von Neumann at the also circulated his in 1945. The Manchester Small-Scale Experimental Machine, nicknamed Baby, was the world's first. It was built at the by, and, and ran its first program on 21 June 1948. It was designed as a for the, the first digital storage device.
Although the computer was considered 'small and primitive' by the standards of its time, it was the first working machine to contain all of the elements essential to a modern electronic computer. As soon as the SSEM had demonstrated the feasibility of its design, a project was initiated at the university to develop it into a more usable computer, the. The Mark 1 in turn quickly became the prototype for the, the world's first commercially available general-purpose computer. Built by, it was delivered to the in February 1951.
At least seven of these later machines were delivered between 1953 and 1957, one of them to labs in. In October 1947, the directors of British catering company decided to take an active role in promoting the commercial development of computers. The computer became operational in April 1951 and ran the world's first regular routine office computer. A The bipolar was invented in 1947.
From 1955 onwards transistors replaced in computer designs, giving rise to the 'second generation' of computers. Compared to vacuum tubes, transistors have many advantages: they are smaller, and require less power than vacuum tubes, so give off less heat. Silicon junction transistors were much more reliable than vacuum tubes and had longer, indefinite, service life.
Transistorized computers could contain tens of thousands of binary logic circuits in a relatively compact space. At the, a team under the leadership of designed and built a machine using the newly developed instead of valves. Their first and the first in the world, was, and a second version was completed there in April 1955. However, the machine did make use of valves to generate its 125 kHz clock waveforms and in the circuitry to read and write on its magnetic, so it was not the first completely transistorized computer.
That distinction goes to the of 1955, built by the electronics division of the. Integrated circuits The next great advance in computing power came with the advent of the. The idea of the integrated circuit was first conceived by a radar scientist working for the of the,. Dummer presented the first public description of an integrated circuit at the Symposium on Progress in Quality Electronic Components in on 7 May 1952.
The first practical ICs were invented by at and. Kilby recorded his initial ideas concerning the integrated circuit in July 1958, successfully demonstrating the first working integrated example on 12 September 1958. In his patent application of 6 February 1959, Kilby described his new device as 'a body of semiconductor material. Wherein all the components of the electronic circuit are completely integrated'. Noyce also came up with his own idea of an integrated circuit half a year later than Kilby. His chip solved many practical problems that Kilby's had not.
Produced at Fairchild Semiconductor, it was made of, whereas Kilby's chip was made of. This new development heralded an explosion in the commercial and personal use of computers and led to the invention of the. While the subject of exactly which device was the first microprocessor is contentious, partly due to lack of agreement on the exact definition of the term 'microprocessor', it is largely undisputed that the first single-chip microprocessor was the, designed and realized by,, and Stanley Mazor. Mobile computers become dominant With the continued miniaturization of computing resources, and advancements in portable battery life, grew in popularity in the 2000s. The same developments that spurred the growth of laptop computers and other portable computers allowed manufacturers to integrate computing resources into cellular phones. These so-called and run on a variety of operating systems and have become the dominant computing device on the market, with manufacturers reporting having shipped an estimated 237 million devices in 2Q 2013. Types Computers are typically classified based on their uses: Based on uses • • Digital computer • Based on sizes • • • • • • • Hardware.
Diagram showing how a particular instruction would be decoded by the control system 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 control signals that activate other parts of the computer. Control systems in advanced computers may change the order of execution of some instructions to improve performance. A key component common to all CPUs is the, a special memory cell (a ) that keeps track of which location in memory the next instruction is to be read from. 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 ). 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, which runs a program that causes all of these events to happen. Central processing unit (CPU) The control unit, ALU, and registers are collectively known as a (CPU).
Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single called a. Arithmetic logic unit (ALU). Main article: The ALU is capable of performing two classes of operations: arithmetic and logic. The set of arithmetic operations that a particular ALU supports may be limited to addition and subtraction, or might include multiplication, division, functions such as sine, cosine, etc., and. Some can only operate on whole numbers () whilst others use to represent, 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 (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:,,, and. These can be useful for creating complicated and processing.
Computers may contain multiple ALUs, allowing them to process several instructions simultaneously. And computers with and features often contain ALUs that can perform arithmetic on and. 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 in groups of eight bits (called a ). 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 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 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: • or RAM • or ROM RAM can be read and written to anytime the CPU commands it, but ROM is preloaded with data and software that never changes, therefore 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 that orchestrates loading the computer's from the hard disk drive into RAM whenever the computer is turned on or reset. In, which frequently do not have disk drives, all of the required software may be stored in ROM. Software stored in ROM is often called, because it is notionally more like hardware than software. 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. In more sophisticated computers there may be one or more RAM, 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). Are common storage devices used with computers. I/O is the means by which a computer exchanges information with the outside world. Devices that provide input or output to the computer are called. On a typical personal computer, peripherals include input devices like the keyboard and, and output devices such as the and., drives and serve as both input and output devices. Is another form of I/O.
I/O devices are often complex computers in their own right, with their own CPU and memory. A might contain fifty or more tiny computers that perform the calculations necessary to display. [ ] Modern contain many smaller computers that assist the main CPU in performing I/O. A 2016-era flat screen display contains its own computer circuitry. Main article: 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. One means by which this is done is with a special signal called an, 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. Before the era of inexpensive computers, the principal 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, but 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 simultaneously without unacceptable speed loss.
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, and. Multiprocessor and (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. 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,, and applications, as well as with other so-called ' tasks. Main article: Software refers to parts of the computer which do not have a material form, such as programs, data, protocols, etc. Software is that part of a computer system that consists of encoded information or computer instructions, in contrast to the physical from which the system is built. Computer software includes, and related non-executable, such as. Computer hardware and software require each other and neither can be realistically used on its own. When software is stored in hardware that cannot easily be modified, such as with in an computer, it is sometimes called 'firmware'.
Replica of the Small-Scale Experimental Machine (SSEM), the world's first, at the in Manchester, England This section applies to most common -based computers. In most cases, computer instructions are simple: add one number to another, move some data from one location to another, send a message to some external device, etc.
These instructions are read from the computer's and are generally carried out () in the order they were given. However, there are usually specialized instructions to tell the computer to jump ahead or backwards to some other place in the program and to carry on executing from there. These are called 'jump' instructions (or ). Furthermore, jump instructions may be made to happen so that different sequences of instructions may be used depending on the result of some previous calculation or some external event.
Many computers directly support by providing a type of jump that 'remembers' the location it jumped from and another instruction to return to the instruction following that jump instruction. Program execution might be likened to reading a book. While a person will normally read each word and line in sequence, they may at times jump back to an earlier place in the text or skip sections that are not of interest. Similarly, a computer may sometimes go back and repeat the instructions in some section of the program over and over again until some internal condition is met.
This is called the within the program and it is what allows the computer to perform tasks repeatedly without human intervention. Comparatively, a person using a pocket can perform a basic arithmetic operation such as adding two numbers with just a few button presses. But to add together all of the numbers from 1 to 1,000 would take thousands of button presses and a lot of time, with a near certainty of making a mistake.
On the other hand, a computer may be programmed to do this with just a few simple instructions. The following example is written in the. Begin: addi $8, $0, 0 # initialize sum to 0 addi $9, $0, 1 # set first number to add = 1 loop: slti $10, $9, 1000 # check if the number is less than 1000 beq $10, $0, finish # if odd number is greater than n then exit add $8, $8, $9 # update sum addi $9, $9, 1 # get next number j loop # repeat the summing process finish: add $2, $8, $0 # put sum in output register Once told to run this program, the computer will perform the repetitive addition task without further human intervention. It will almost never make a mistake and a modern PC can complete the task in a fraction of a second. Machine code In most computers, individual instructions are stored as with each instruction being given a unique number (its operation code or for short).
The command to add two numbers together would have one opcode; the command to multiply them would have a different opcode, and so on. The simplest computers are able to perform any of a handful of different instructions; the more complex computers have several hundred to choose from, each with a unique numerical code. Since the computer's memory is able to store numbers, it can also store the instruction codes.
This leads to the important fact that entire programs (which are just lists of these instructions) can be represented as lists of numbers and can themselves be manipulated inside the computer in the same way as numeric data. The fundamental concept of storing programs in the computer's memory alongside the data they operate on is the crux of the von Neumann, or stored program [ ], architecture. In some cases, a computer might store some or all of its program in memory that is kept separate from the data it operates on. This is called the after the computer. Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in. While it is possible to write computer programs as long lists of numbers () and while this technique was used with many early computers, it is extremely tedious and potentially error-prone to do so in practice, especially for complicated programs.
Instead, each basic instruction can be given a short name that is indicative of its function and easy to remember – a such as ADD, SUB, MULT or JUMP. These mnemonics are collectively known as a computer's. Converting programs written in assembly language into something the computer can actually understand (machine language) is usually done by a computer program called an assembler. Main article: Though considerably easier than in machine language, writing long programs in assembly language is often difficult and is also error prone. Therefore, most practical programs are written in more abstract that are able to express the needs of the more conveniently (and thereby help reduce programmer error). High level languages are usually 'compiled' into machine language (or sometimes into assembly language and then into machine language) using another computer program called a.
High level languages are less related to the workings of the target computer than assembly language, and more related to the language and structure of the problem(s) to be solved by the final program. It is therefore often possible to use different compilers to translate the same high level language program into the machine language of many different types of computer. This is part of the means by which software like video games may be made available for different computer architectures such as personal computers and various.
Fourth-generation languages. This section does not any. Unsourced material may be challenged and. (July 2012) () Program design of small programs is relatively simple and involves the analysis of the problem, collection of inputs, using the programming constructs within languages, devising or using established procedures and algorithms, providing data for output devices and solutions to the problem as applicable. As problems become larger and more complex, features such as subprograms, modules, formal documentation, and new paradigms such as object-oriented programming are encountered. Large programs involving thousands of line of code and more require formal software methodologies.
The task of developing large systems presents a significant intellectual challenge. Producing software with an acceptably high reliability within a predictable schedule and budget has historically been difficult; the academic and professional discipline of concentrates specifically on this challenge.
The actual first computer bug, a moth found trapped on a relay of the Harvard Mark II computer Errors in computer programs are called '. They may be benign and not affect the usefulness of the program, or have only subtle effects. But in some cases, they may cause the program or the entire system to ', becoming unresponsive to input such as clicks or keystrokes, to completely fail, or to. Otherwise benign bugs may sometimes be harnessed for malicious intent by an unscrupulous user writing an, code designed to take advantage of a bug and disrupt a computer's proper execution.
Bugs are usually not the fault of the computer. Since computers merely execute the instructions they are given, bugs are nearly always the result of programmer error or an oversight made in the program's design. Admiral, an American computer scientist and developer of the first, is credited for having first used the term 'bugs' in computing after a dead moth was found shorting a relay in the computer in September 1947.
Firmware Firmware is the technology which has the combination of both hardware and software such as BIOS chip inside a computer. This chip (hardware) is located on the motherboard and has the BIOS set up (software) stored in it. Networking and the Internet. Visualization of a portion of the on the Internet Computers have been used to coordinate information between multiple locations since the 1950s. Military's system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems such as. In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology.
The effort was funded by ARPA (now ), and the that resulted was called the. 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, combined with the development of cheap, fast networking technologies like and 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.
See also: A computer does not need to be, nor even have a, nor, nor even a. While popular usage of the word 'computer' is synonymous with a personal electronic computer, the modern definition of a computer is literally: ' A device that computes, especially a programmable [usually] electronic machine that performs high-speed mathematical or logical operations or that assembles, stores, correlates, or otherwise processes information.' Any device which processes information qualifies as a computer, especially if the processing is purposeful. [ ] Unconventional computing. Further information: Historically, computers evolved from and eventually from to. However, conceptually computational systems as as a personal computer can be built out of almost anything. For example, a computer can be made out of billiard balls (); an often quoted example.
[ ] More realistically, modern computers are made out of made of. Future There is active research to make computers out of many promising new types of technology, such as,,, and. Most computers are universal, and are able to calculate any, and are limited only by their memory capacity and operating speed. However different designs of computers can give very different performance for particular problems; for example quantum computers can potentially break some modern encryption algorithms (by ) very quickly. Computer architecture paradigms There are many types of: • vs. • (NUMA) computers • vs.
• Of all these, a quantum computer holds the most promise for revolutionizing computing. Are a common abstraction which can apply to most of the above or paradigms.
The ability to store and execute lists of instructions called makes computers extremely versatile, distinguishing them from. The is a mathematical statement of this versatility: any computer with a is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, any type of computer (,,, etc.) is able to perform the same computational tasks, given enough time and storage capacity. Artificial intelligence A computer will solve problems in exactly the way it is programmed to, without regard to efficiency, alternative solutions, possible shortcuts, or possible errors in the code.
Computer programs that learn and adapt are part of the emerging field of and. Artificial intelligence based products generally fall into two major categories: rule based systems and pattern recognition systems. Rule based systems attempt to represent the rules used by human experts and tend to be expensive to develop.
Pattern based systems use data about a problem to generate conclusions. Examples of pattern based systems include voice recognition, font recognition, translation and the emerging field of on-line marketing. Professions and organizations As the use of computers has spread throughout society, there are an increasing number of careers involving computers.
Hardware-related,,,,, Software-related,,,,,,,,, The need for computers to work well together and to be able to exchange information has spawned the need for many standards organizations, clubs and societies of both a formal and informal nature. Standards groups,,,,, Professional societies,,,, / groups,, See also.