Today, I want to discuss we all of you about COMPUTER.
First of all,what is Computer?For sure most of you what computer it is.Computer is something that can less human energy and something that easier for man kind to settle down their project or work.
If you use a desktop computer, you might already know that there isn't any single part called the "computer." A computer is really a system of many parts working together. The physical parts, which you can see and touch, are collectively called hardware. (Software, on the other hand, refers to the instructions, or programs, that tell the hardware what to do.)
The illustration below shows the most common hardware in a desktop computer system. Your system may look a little different, but it probably has most of these parts. A laptop computer has similar parts but combines them into a single notebook-sized package.
System Unit
The system unit is the core of a computer system. Usually it's a rectangular box placed on or underneath your desk. Inside this box are many electronic components that process information. The most important of these components is the central processing unit (CPU), or microprocessor, which acts as the "brain" of your computer. Another component israndom access memory (RAM), which temporarily stores information that the CPU uses while the computer is on. The information stored in RAM is erased when the computer is turned off.
Almost every other part of your computer connects to the system unit using cables. The cables plug into specific ports (openings), typically on the back of the system unit. Hardware that is not part of the system unit is sometimes called a peripheral device ordevice.
Keyboard
A keyboard is used mainly for typing text into your computer. Like the keyboard on a typewriter, it has keys for letters and numbers, but it also has special keys:
The function keys, found on the top row, perform different functions depending on where they are used.
The numeric keypad, located on the right side of most keyboards, allows you to enter numbers quickly.
The navigation keys, such as the arrow keys, allow you to move your position within a document or webpage.
Monitor
A monitor displays information in visual form, using text and graphics. The portion of the monitor that displays the information is called the screen. Like a television screen, a computer screen can show still or moving pictures.
There are two basic types of monitors: CRT (cathode ray tube) monitors and LCD (liquid crystal display) monitors. Both types produce sharp images, but LCD monitors have the advantage of being much thinner and lighter. CRT monitors, however, are generally more affordable.
Speakers
Speakers are used to play sound. They may be built into the system unit or connected with cables. Speakers allow you to listen to music and hear sound effects from your computer.
For your information,we have done with our second assignment which is Assesment in school that related to the network of the school.
Due to date,my group and I choose SMK Aminuddin Baki in order to complete this assignment.
Before that,let's me introduce my group.There are :
Nurul Ainina binti Kamid
Nursyidatul Najah binti Mohd Rawi
Syuhada Fatieha binti Bachik
Our assesment is on 19 April 2012.For your addition information,we choose school as our assesment because we want to related on what we have study and we want to look the real things that apply.Not just theory like what we study in the class.
The others point on what we do at the school will be presented at the lecture class.
Edinburgh University has developed a technique, which allows neurons to grow in fine, detailed patterns on the surface of tiny computer chips.
Neurons are the basic cells of the human nervous system.
The scientists said the development may eventually enable chips to replace damaged nerve or muscle fibres.
They also said the development could possibly be used in the development of prosthetics in the future.
During the chip manufacturing process, the scientists printed patterns on the smooth silicon surface.
' It is going towards the realms of science fiction - there is a definite Incredible Hulk feel about it '
Prof Alan Murray
Edinburgh University
The chip was then dipped in a patented mixture of proteins, and neurons grew along the patterns on the surface.
The technique also works with stem cells.
It is hoped the method will eventually enable any type of tissue to be grown on a tailor-made pathway and implanted as prosthetic tissue in the body.
Professor Alan Murray, head of Edinburgh University's School of Engineering and Electronics, who led the research, said: "This is a small but important step on the path towards the long-term goal of many scientists and medical experts - to develop surgical implants using silicon chips.
"We can now make silicon chips with circuitry as well as pathways where cells can grow in the body.
"One of the areas this could be used in is prosthetics - if we can cause cells from damaged tissues to grow where we want.
"It is going towards the realms of science fiction - there is a definite Incredible Hulk feel about it."
He added: "We also hope that, rather sooner than this, the technique will allow better methods of drug discovery and reduce the need for animal testing, as new medicines could be tested on chips rather than in live creatures."
The research was funded by the Engineering and Physical Sciences Research Council.
A web search engine is designed to search for information on the World Wide Web. The search results are generally presented in a list of results often referred to as search engine results pages (SERPs). The information may consist of web pages, images, information and other types of files. Some search engines also mine data available in databases or open directories. Unlike web directories, which are maintained only by human editors, search engines also maintain real-time information by running an algorithm on a web crawler.
Web search engines work by storing information about many web pages, which they retrieve from the HTML itself. These pages are retrieved by a Web crawler (sometimes also known as a spider) — an automated Web browser which follows every link on the site. Exclusions can be made by the use of robots.txt. The contents of each page are then analyzed to determine how it should be indexed (for example, words are extracted from the titles, headings, or special fields called meta tags). Data about web pages are stored in an index database for use in later queries. A query can be a single word. The purpose of an index is to allow information to be found as quickly as possible. Some search engines, such as Google, store all or part of the source page (referred to as a cache) as well as information about the web pages, whereas others, such as AltaVista, store every word of every page they find. This cached page always holds the actual search text since it is the one that was actually indexed, so it can be very useful when the content of the current page has been updated and the search terms are no longer in it. This problem might be considered to be a mild form of linkrot, and Google's handling of it increases usability by satisfying user expectations that the search terms will be on the returned webpage. This satisfies the principle of least astonishment since the user normally expects the search terms to be on the returned pages. Increased search relevance makes these cached pages very useful, even beyond the fact that they may contain data that may no longer be available elsewhere.
When a user enters a query into a search engine (typically by using keywords), the engine examines its index and provides a listing of best-matching web pages according to its criteria, usually with a short summary containing the document's title and sometimes parts of the text. The index is built from the information stored with the data and the method by which the information is indexed. Unfortunately, there are currently no known public search engines that allow documents to be searched by date. Most search engines support the use of the boolean operators AND, OR and NOT to further specify the search query. Boolean operators are for literal searches that allow the user to refine and extend the terms of the search. The engine looks for the words or phrases exactly as entered. Some search engines provide an advanced feature called proximity search which allows users to define the distance between keywords. There is also concept-based searching where the research involves using statistical analysis on pages containing the words or phrases you search for. As well, natural language queries allow the user to type a question in the same form one would ask it to a human. A site like this would be ask.com.
The usefulness of a search engine depends on the relevance of the result set it gives back. While there may be millions of web pages that include a particular word or phrase, some pages may be more relevant, popular, or authoritative than others. Most search engines employ methods to rank the results to provide the "best" results first. How a search engine decides which pages are the best matches, and what order the results should be shown in, varies widely from one engine to another. The methods also change over time as Internet usage changes and new techniques evolve. There are two main types of search engine that have evolved: one is a system of predefined and hierarchically ordered keywords that humans have programmed extensively. The other is a system that generates an "inverted index" by analyzing texts it locates. This second form relies much more heavily on the computer itself to do the bulk of the work.
Most Web search engines are commercial ventures supported by advertising revenue and, as a result, some employ the practice of allowing advertisers to pay money to have their listings ranked higher in search results. Those search engines which do not accept money for their search engine results make money by running search related ads alongside the regular search engine results. The search engines make money every time someone clicks on one of these ads.
ADVANTAGES AND DISADVANTAGES OF WEB SEARCHING
Some of advantages of web searching are :
Indexes for search engines can be very large because they are created by software.
They are very simple to search.
Some of disadvantages of web searching are :
Sites are randomly crawled and indexed for keywords by software. Not even the largest search engine can crawl all of the web, it is too vast.
Results are not evaluated for quality.
Searching can result in far too many results to check properly. Results may not be in the most relevant order.
More authorative sources maybe buried due to lack of popularity.
Computer networking devices are units that mediate data in a computer network.[1][2] Computer networking devices are also called network equipment, Intermediate Systems (IS)[citation needed] or InterWorking Unit (IWU).[citation needed] Units which are the last receiver or generate data are called hosts or data terminal equipment.[citation needed]
The most common kind of networking hardware today is copper-based Ethernetadapters, helped largely by its standard inclusion on most modern computer systems. Wireless networking has become increasingly popular, however, especially for portable and handheld devices.
Other diverse devices which may be considered networking hardware include mobile phones, PDAs and even modern coffee machines. As technology grows and IP-based networks are integrated into building infrastructure and household utilities, network hardware becomes an ambiguous statement owing to the increasing number of "network capable" endpoints.
Computer Networking Devices
File 0r Network Server
One or more network servers is a part of nearly every local area network.These are very fast computers with a large amount of RAM and storage space, along with a one or more fast network interface card(s). The network operating system provides tools to share server resources and information with network users. A sophisticated permissions-handling system is included, so that access to sensitive information can be carefully tailored to the needs of the users. For small networks, a singe network server may provide access control, file sharing, printer sharing, email, database, and other services.
The network server may be responding to requests from many network users simultaneously. For example, it may be asked to load a word processor program to one workstation, receive a database file from another workstation, and store an e-mail message during the same time period. This requires a computer that can store and quickly share large amounts of information. When configuring such a server, budget is usually the controlling factor. The following guidelines should be followed:
Fastest processor(s)
Large amount of RAM
multiple large, fast hard drives
Extra expansion slots
Fast network interface card(s)
Workstations
Computers that humans use are broadly categorized as workstations. A typical workstation is a computer that is configured with a network interface card, networking software, and the appropriate cables. Workstations do not necessarily need large storage hard drives, because files can be saved on the file server. Almost any computer can serve as a network workstation.
Network Interface Card
The network interface card (NIC) provides the physical connection between the network and the computer workstation. Most NICs are internal, and they are included in the purchase of most computers. Network interface cards are a major factor in determining the speed and performance of a network. It is a good idea to use the fastest network card available for the type of workstation you are using.
The most common network interface connections are Ethernet cards and wireless adapters.
Ethernet Card
Ethernet cards are usually included with a computer, although additional ethernet cards can be purchased and installed on most computers,. Ethernet cards can contain connections for either coaxial or twisted pair cables (or both) (See fig. 1). If it is designed for coaxial cable, the connection will be BNC. If it is designed for twisted pair, it will have a RJ-45 connection. Some Ethernet cards also contain an AUI connector. This can be used to attach coaxial, twisted pair, or fiber optics cable to an Ethernet card. When this method is used there is always an external transceiver attached to the workstation. Only the RJ-45 connector is found on most modern ethernet cards.
An ethernet switch is a device that provides a central connection point for cables from workstations, servers, and peripherals. In a star topology, twisted-pair wire is run from each workstation to a central switch/hub. Most switches are active, that is they electrically amplify the signal as it moves from one device to another. The predecessor of the switch was the hub, which broadcasted all inbound packets out all ports of the device, creating huge amounts of unnecessary network traffic. Modern switches build a port map of all IP address which respond on each port, and only broadcasts on all ports when it doesn't have a packet's target IP address already in its port map. Switches are:
Usually configured with 8, 12, or 24 RJ-45 ports
Often used in a star or tree topology
Available as "managed" or "unmanaged", with the later less expensive, but adequate for smaller networks
direct replacements for hubs, immediately reducing network traffic in most networks
Usually installed in a standardized metal rack that also may store network servers, bridges, or routers
An ethernet switch is a device that provides a central connection point for cables from workstations, servers, and peripherals. In a star topology, twisted-pair wire is run from each workstation to a central switch/hub. Most switches are active, that is they electrically amplify the signal as it moves from one device to another. The predecessor of the switch was the hub, which broadcasted all inbound packets out all ports of the device, creating huge amounts of unnecessary network traffic. Modern switches build a port map of all IP address which respond on each port, and only broadcasts on all ports when it doesn't have a packet's target IP address already in its port map. Switches are:
-Usually configured with 8, 12, or 24 RJ-45 ports
-Often used in a star or tree topology
-Available as "managed" or "unmanaged", with the later less expensive, but adequate for -smaller networks
-direct replacements for hubs, immediately reducing network traffic in most networks
-Usually installed in a standardized metal rack that also may store network servers, bridges, or routers Ethernet Card
Switches
An ethernet switch is a device that provides a central connection point for cables from workstations, servers, and peripherals. In a star topology, twisted-pair wire is run from each workstation to a central switch/hub. Most switches are active, that is they electrically amplify the signal as it moves from one device to another. The predecessor of the switch was the hub, which broadcasted all inbound packets out all ports of the device, creating huge amounts of unnecessary network traffic. Modern switches build a port map of all IP address which respond on each port, and only broadcasts on all ports when it doesn't have a packet's target IP address already in its port map. Switches are:
Usually configured with 8, 12, or 24 RJ-45 ports
Often used in a star or tree topology
Available as "managed" or "unmanaged", with the later less expensive, but adequate for smaller networks
direct replacements for hubs, immediately reducing network traffic in most networks
Since a signal loses strength as it passes along a cable, it is often necessary to boost the signal with a device called a repeater. The repeater electrically amplifies the signal it receives and rebroadcasts it. Repeaters can be separate devices or they can be incorporated into a concentrator. They are used when the total length of your network cable exceeds the standards set for the type of cable being used.
A good example of the use of repeaters would be in a local area network using a star topology with unshielded twisted-pair cabling. The length limit for unshielded twisted-pair cable is 100 meters. The most common configuration is for each workstation to be connected by twisted-pair cable to a multi-port active concentrator. The concentrator amplifies all the signals that pass through it allowing for the total length of cable on the network to exceed the 100 meter limit.
Repeaters
Bridges
A bridge is a device that allows you to segment a large network into two smaller, more efficient networks. If you are adding to an older wiring scheme and want the new network to be up-to-date, a bridge can connect the two.
A bridge monitors the information traffic on both sides of the network so that it can pass packets of information to the correct location. Most bridges can "listen" to the network and automatically figure out the address of each computer on both sides of the bridge. The bridge can inspect each message and, if necessary, broadcast it on the other side of the network.
The bridge manages the traffic to maintain optimum performance on both sides of the network. You might say that the bridge is like a traffic cop at a busy intersection during rush hour. It keeps information flowing on both sides of the network, but it does not allow unnecessary traffic through. Bridges can be used to connect different types of cabling, or physical topologies. They must, however, be used between networks with the same protocol.
Routers
Routers are the traffic directors of the global internet. All routers maintain complex routing tables which allow them to determine appropriate paths for packets destined for any address. Routers communicate with each other, and forward network packets out of or into a network. Here's an example:
You want to search for something on the internet using a search engine. You open a browser on your workstation. The browser opens to a blank page (not usually the default, but appropriate for this example). You type "http://www.google.com" into the URL (Universal Resource Locator) address line of the browser. The browser software packages up the URL you typed, and sends it with a request for an IP address to the DNS (Domain Name Server) that has been set in your network adapter's configuration. The domain server returns an IP, such as 74.125.67.103 (actual address returned by DNS for google.com on June 7th, 2011). The browser ships the request for that IP address off to the network card, which bundles the request into an ethernet packet, destined for 74.125.67.103. The network card sends the packet to the gateway of your network, which opens the header of the packet, and makes a determination that the packet is traveling out of your network, in search of 74.125.67.103. Your network's router has routing tables which it has been building from communicating with other routers, and potentially augmented with "static routes", which are specific paths added by your network's administrators to make the task of accessing certain networks easier, or faster, or in some cases, not possible. In this case, I find that my router knows about another router at my ISP(Internet Service Provider), which in turn has several more routers that are all on networks of which I am just a small node, much like finding an atom of a molecule of a piece of dust on a rock on a moon of a planet of a sun of a galaxy of the universe. In any case, the packet gets passed from router to router, each time moving out of the subnets of the packet sender, towards a router that will know where the desired server is. The packet finally reaches the router of the network at 74.125.67.103, which dutifully delivers the packet to the server at that IP address. The server carefully crafts a response, and sends a reply back, which follows the same process to get the response "Yes. Go ahead" back to the requester. Whew. And that's just the initial request.
While bridges know the addresses of all computers on each side of the network, routers know the addresses other routers which in turn know about their own networks. Routers can even "listen" to entire networks to determine which sections are busiest -- they can then redirect data around those sections until traffic congestion clears.
So, routers are network gateways. They move network packets from one network to another, and many can convert from one network protocol to another as necessary. Routers select the best path to route a message, based on the destination address of the packet. The router can direct traffic to prevent head-on collisions, and is smart enough to know when to direct traffic along back roads and shortcuts.
If you have a school LAN that you want to connect to the Internet, you will need to purchase a router. In this case, the router serves as the forwarder between the information on your LAN and the Internet. It also determines the best route to send the data over the Internet.
Synchronous and asynchronous transmissions are two different methods of transmissionsynchronization. Synchronous transmissions are synchronized by an external clock, while asynchronous transmissions are synchronized by special signals along the transmission medium.
The send, receive, and reply operations may be synchronous or asynchronous. A synchronous operation blocks a process till the operation completes. An asynchronous operation is non-blocking and only initiates the operation. The caller could discover completion by some other mechanism discussed later.
The notion of synchronous operations requires an understanding of what it means for an operation to complete. In the case of remote assignment, both the send and receive complete when the message has been delivered to the receiver. In the case of remote procedure call, the send, receive, and reply complete when the result has been delivered to the sender, assuming there is a return value. Otherwise, the send and receive complete when the procedure finishes execution. During the time the procedure is executing, the sender and receiver are in a rendezvous, as mentioned before.
Note that synchronous/asynchronous implies blocking/not blocking but not vice versa, that is, not every blocking operation is synchronous and not every non blocking operation is asynchronous. For instance, a send that blocks till the receiver machine has received the message is blocking but not synchronous since the receiver process may not have received it. Similarly, we will see later a Xinu receive that is non-blocking but is not asynchronous. These definitions of synchronous/asynchronous operations are similar but not identical to the ones given in your text books, which tend to equate synchronous with blocking.
Asynchronous message passing allows more parallelism. Since a process does not block, it can do some computation while the message is in transit. In the case of receive, this means a process can express its interest in receving messages on multiple ports simultaneously. (The select primitive discussed later provides this facility for synchronous receives). In a synchronous system, such parallelism can be achieved by forking a separate process for each concurrent operation, but this approach incurs the cost of extra process management. This cost is typically bearable with lwps but not hwps.
Asynchronous message passing introduces several problems. What happens if a message cannot be delivered? The sender may never wait for delivery of the message, and thus never hear about the error. Similarly, a mechanism is needed to notify an asynchronous receiver that a message has arrived. The operation invoker could learn about completion/errors by polling, getting a software interrupt, or by waiting explicitly for completion later using a special sycnhronous wait call. An asynchronous operation needs to return a call/transaction id if the application needs to be later notified about the operation. At notification time, this id would be placed in some global location or passed as an argument to a handler or wait call.
Another problem related to asynchronous message passing has to do with buffering. If messages sent asynchronously are buffered in a space managed by the OS, then a process may fill this space by flooding the system with a large number of messages.
This number is an exclusive number all information technology devices (printers, routers, modems, et al) use which identifies and allows them the ability to communicate with each other on a computer network. There is a standard of communication which is called an Internet Protocol standard. In laymans terms it is the same as your home address.
In order for you to receive snail mail at home the sending party must have your correct mailing address (IP address) in your town (network) or you do not receive bills, pizza coupons or your tax refund. The same is true for all equipment on the internet. Without this specific address, information cannot be received. IP addresses may either be assigned permanently for an Email server/Business server or a permanent home resident or temporarily, from a pool of available addresses (first come first serve) from your Internet Service Provider. A permanent number may not be available in all areas and may cost extra so be sure to ask your ISP.
DOMAIN NAME SYSTEM (DNS)
This allows the IP address to be translated to words. It is much easier for us to remember a word than a series of numbers. The same is true for email addresses.
For example, it is much easier for you to remember a web address name such as whatismyip.com than it is to remember 192.168.1.1 or in the case of email it is much easier to remember email@somedomain.com than email@192.168.1.1.
DYNAMIC IP ADDRESS
One that is not static and could change at any time. This type is issued to you from a pool of addresses allocated by your ISP or DHCP Server. This is for a large number of customers that do not require the same address all the time for a variety of reasons. Your computer will automatically get this number as it logs on to the network and saves you the trouble of having to know details regarding the specific network configurations. This number can be assigned to anyone using a dial-up connection, Wireless and High Speed Internet connections. If you need to run your own email server or web server, it would be best to have a static IP address.
STATIC IP ADDRESS
One that is fixed and never changes. This is in contrast to a dynamic IP address which may change at any time. Most ISP's can offer to assign a single static IP or a block of static IP's for a few extra bucks a month and may require you upgrading to a business account.
IPv4
Currently used by most network devices. However, with more and more computers accessing the internet, IPv4 IPs are running out quickly. Just like in a city, addresses have to be created for new neighborhoods but, if your neighborhood gets too large, you will have to come up with an entire new pool of addresses. IPv4 is limited to 4,294,967,296 IPs.
IPv5
This is an experimental protocol for UNIX based systems. In keeping with standard UNIX (a computer Operating System) release conventions, all odd-numbered versions are considered experimental. It was never intended to be used by the general public.
IPv6
The replacement for the aging IPv4. The estimated number of unique IPs for IPv6 is 340,282,366,920,938,463,463,374,607,431,768,211,456 or 2^128.
The old and current standard of IPs was this: 192.168.100.100 the new way can be written different ways but means the same and are all valid.
