Computer + Internet + Memory

What is a proxy server?

A proxy server provides a gateway between users and the internet. It is a server, referred to as an "intermediary" because it goes between end-users and the web pages they visit online. It can have various functionalities and advantages such as filtering, logging, and hiding the user's IP address.

What is a router?

A router is the most intelligent and complex of the three network connection devices. Rather than just forwarding data packets to other devices in a single network, routers are designed to forward data packets between two or more networks, as well as direct traffic between them. They are typically located at gateways and can be programmed to understand, direct, and manipulate network traffic. Many modern routers are designed to integrate the capabilities of a switch and hub router all in a single device. Depending on the application, routers range in size from small broadband devices to large industrial wireless routers.

What is an ISP?

An Internet Service Provider (ISP) is the industry term for the company that is able to provide you with access to the Internet, typically from a computer.

How is computer software stored on the computer?

Computer software consists of both programs and data. Programs consist of instructions for the processor. Data can be any information that a program needs: character data, numerical data, image data, audio data, and countless other types. Both programs and data are saved in computer memory in the same way. The electronics of computer memory (both main memory and secondary memory) make no distinction between programs and data. Computer systems use memory for either programs or data, as needed.

What are cookies?

Cookies are text files with small pieces of data — like a username and password — that are used to identify your computer as you use a computer network. Specific cookies known as HTTP cookies are used to identify specific users and improve your web browsing experience. Data stored in a cookie is created by the server upon your connection. This data is labeled with an ID unique to you and your computer. When the cookie is exchanged between your computer and the network server, the server reads the ID and knows what information to specifically serve to you.

What is encryption?

Encryption is a way to conceal information by altering it so that it appears to be random data. Encryption is essential for security on the Internet.

What is XHR?

XMLHttpRequest (XHR) is an API in the form of an object whose methods transfer data between a web browser and a web server. The object is provided by the browser's JavaScript environment.

What is the difference between a process and a thread?

1. A program in execution is often referred as process. A thread is a subset (part) of the process. 2. A process consists of multiple threads. A thread is a smallest part of the process that can execute concurrently with other parts (threads) of the process. 3. A process is sometime referred as task. A thread is often referred as lightweight process. 4. A process has its own address space. A thread uses the process's address space and share it with the other threads of that process.

What are the different layers that the TCP/IP protocol goes through?

1. Datalink layer: (also called the link layer, network interface layer, or physical layer) handles the physical parts of sending and receiving data using the Ethernet cable, wireless network, network interface card, device driver in the computer, and so on. 2. Internet layer: (also called the network layer) controls the movement of packets around the network. 3. Transport layer: provides a reliable data connection between two devices. It divides the data in packets, acknowledges the packets that it has received from the other device, and makes sure that the other device acknowledges the packets it receives. 4. Application layer: the group of applications that require network communication. This is what the user typically interacts with, such as email and messaging. Because the lower layers handle the details of communication, the applications don't need to concern themselves with this.

What are cookies used for?

1. Session management. For example, cookies let websites recognize users and recall their individual login information and preferences, such as sports news versus politics. 2. Personalization. Customized advertising is the main way cookies are used to personalize your sessions. You may view certain items or parts of a site, and cookies use this data to help build targeted ads that you might enjoy. 3. Tracking. Shopping sites use cookies to track items users previously viewed, allowing the sites to suggest other goods they might like and keep items in shopping carts while they continue shopping.

What is a URL?

A URL (Uniform Resource Locator) is a specific type of URI (Universal Resource Identifier). A URL normally locates an existing resource on the Internet. A URL is used when a web client makes a request to a server for a resource.

What are the different components of a URL and what are they responsible for?

A URL for HTTP (or HTTPS) is normally made up of three or four components: 1. A scheme. The scheme identifies the protocol to be used to access the resource on the Internet. It can be HTTP (without SSL) or HTTPS (with SSL). 2. A host. The host name identifies the host that holds the resource. For example, www.example.com. A server provides services in the name of the host, but hosts and servers do not have a one-to-one mapping. Host names can also be followed by a port number. Well-known port numbers for a service are normally omitted from the URL. Most servers use the well-known port numbers for HTTP and HTTPS , so most HTTP URLs omit the port number. 3. A path. The path identifies the specific resource in the host that the web client wants to access. For example, /software/htp/cics/index.html. 4. A query string. If a query string is used, it follows the path component, and provides a string of information that the resource can use for some purpose (for example, as parameters for a search or as data to be processed). The query string is usually a string of name and value pairs; for example, term=bluebird. Name and value pairs are separated from each other by an ampersand (&); for example, term=bluebird&source=browser-search.

What is a network? What is a node?

A computer network is a group of computers that use a set of common communication protocols over digital interconnections for the purpose of sharing resources located on or provided by the network nodes. A node is any physical device within a network of other tools that's able to send, receive, or forward information. A personal computer is the most common node. It's called the computer node or internet node. Modems, switches, hubs, bridges, servers, and printers are also nodes, as are other devices that connect over Wi-Fi or Ethernet. For example, a network connecting three computers and one printer, along with two more wireless devices, has six total nodes. Nodes within a computer network must have some form of identification, like an IP address or MAC address, for other network devices to recognize it. A node without this information, or one that's offline, no longer functions as a node.

What is a firewall?

A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. A firewall typically establishes a barrier between a trusted network and an untrusted network, such as the Internet.

What is a hub?

A hub is a type of device that's commonly used as a connection point for various devices in a Local Area Network (LAN). It works by receiving packets that arrive at one of its multiple ports, copying the packets, and sending them to its other ports so that all LAN segments can see the data. When a single port in the hub responds, all other ports will also receive the response. The hub does not have any capability to distinguish which port it should send a data packet to. As such, all connected devices will receive the response and must determine whether they should accept it or not.In comparison to routers and switches, a hub is the least complex and least expensive device. While they have often been used as a quick and easy way to connect a small network, they are becoming increasingly replaced by switches.

What is a LAN?

A local area network (LAN) is a collection of devices connected together in one physical location, such as a building, office, or home. A LAN can be small or large, ranging from a home network with one user to an enterprise network with thousands of users and devices in an office or school. Regardless of size, a LAN's single defining characteristic is that it connects devices that are in a single, limited area. In contrast, a wide area network (WAN) or metropolitan area network (MAN) covers larger geographic areas. Some WANs and MANs connect many LANs together.

What is a protocol?

A network protocol is an established set of rules that determine how data is transmitted between different devices in the same network. Essentially, it allows connected devices to communicate with each other, regardless of any differences in their internal processes, structure or design.

What is a switch?

A networking switch is a type of hardware that uses packet switching to receive and forward data to its intended destination within a network. Essentially, a switch is a more efficient, more intelligent version of a hub. Perhaps the biggest difference between a hub and a switch is the way that it delivers data packets. Rather than blindly passing along data to all devices in a network, a switch records the addresses of the connected devices. In doing so, it learns which devices are connected to which ports. Then, when a port receives a data packet, the switch reads its destination address and sends it directly to the intended device in the network instead of every single port. As a result, a switch can greatly improve the speed of networks that receive a lot of traffic.

What is an HTTP cookie?

HTTP cookies, or internet cookies, are built specifically for Internet web browsers to track, personalize, and save information about each user's session. A "session" just refers to the time you spend on a site. Cookies are created to identify you when you visit a new website. The web server — which stores the website's data — sends a short stream of identifying info to your web browser. Browser cookies are identified and read by "name-value" pairs. These tell cookies where to be sent and what data to recall. The server only sends the cookie when it wants the web browser to save it. The web browser will store it locally to remember the "name-value pair" that identifies you. If a user returns to that site in the future, the web browser returns that data to the web server in the form of a cookie. This is when your browser will send it back to the server to recall data from your previous sessions. Can be thought of as a coat check where whenever you visit a website a cookie is used as an identifier (like the coat check ticket) to grab the relevant information from the browser.

What is HTTP?

HTTP refers to the Hypertext Transfer Protocol which is is an application layer protocol which allows the fetching of resources, such as HTML documents. It is the foundation of any data exchange on the Web and it is a client-server protocol, which means requests are initiated by the recipient, usually the Web browser. A complete document is reconstructed from the different sub-documents fetched, for instance text, layout description, images, videos, scripts, and more. Communication between clients and servers is done by requests and responses: 1. A client (a browser) sends an HTTP request to the web 2. A web server receives the request 3. The server runs an application to process the request The server returns an HTTP response (output) to the browser 4. The client (the browser) receives the response

What hardware components exist within a computer system?

Hardware components include: the bus, hard disk, USB drives, main memory, processor, monitor (+ video card), and keyboard as well as controllers between the various bits of hardware and the bus. The bus is a group of wires on the main circuit board of the computer. It is a pathway for data flowing between components. Most devices are connected to the bus through a controller which coordinates the activities of the device with the bus.

What is HTTPS?

Hypertext Transfer Protocol Secure is an extension of the Hypertext Transfer Protocol. It is used for secure communication over a computer network, and is widely used on the Internet. In HTTPS, the communication protocol is encrypted using Transport Layer Security or, formerly, Secure Sockets Layer.

What are input and output devices? Name some examples of each.

Input and output devices allow the computer system to interact with the outside world by moving data into and out of the system. An input device is used to bring data into the system. Some input devices are: - Keyboard - Mouse - Microphone - Bar code reader - Graphics tablet An output device is used to send data out of the system. Some output devices are: - Monitor - Printer - Speaker A network interface acts as both input and output. Data flows from the network into the computer, and out of the computer into the network.

How does main memory work?

Main memory is where programs and data are kept when the processor is actively using them. When programs and data become active, they are copied from secondary memory into main memory where the processor can interact with them. A copy remains in secondary memory. Main memory is intimately connected to the processor, so moving instructions and data into and out of the processor is very fast. Main memory is sometimes called RAM. RAM stands for Random Access Memory. "Random" means that the memory cells can be accessed in any order. However, properly speaking, "RAM" means the type of silicon chip used to implement main memory. When people say that a computer has "512 megabytes of RAM" they are talking about how big its main memory is. One megabyte of memory is enough to hold approximately one million (106) characters of a word processing document. Nothing permanent is kept in main memory. Sometimes data are placed in main memory for just a few seconds, only as long as they are needed.

How does secondary memory work?

Secondary memory is where programs and data are kept on a long-term basis. Common secondary storage devices are the hard disk and optical disks. - The hard disk has enormous storage capacity compared to main memory. - The hard disk is usually contained inside the case of a computer. - The hard disk is used for long-term storage of programs and data. - Data and programs on the hard disk are organized into files. - A file is a collection of data on the disk that has a name. A hard disk might have a storage capacity of 500 gigabytes (room for about 500 x 109 characters). This is about 100 times the capacity of main memory. A hard disk is slow compared to main memory. If the disk were the only type of memory the computer system would slow down to a crawl. The reason for having two types of storage is this difference in speed and capacity. Large blocks of data are copied from disk into main memory. The operation is slow, but lots of data is copied. Then the processor can quickly read and write small sections of that data in main memory. When it is done, a large block of data is written to disk. Often, while the processor is computing with one block of data in main memory, the next block of data from disk is read into another section of main memory and made ready for the processor. One of the jobs of an operating system is to manage main storage and disks this way.

What is the TCP/IP model?

TCP/IP stands for Transmission Control Protocol/Internet Protocol. TCP/IP is a set of standardized rules that allow computers to communicate on a network such as the internet. TCP and IP are two separate computer network protocols. IP is the part that obtains the address to which data is sent. TCP is responsible for data delivery once that IP address has been found. The TCP/IP protocol is responsible for breaking information down into packets. It also divides the different communications tasks into layers. Each layer has a different function. Data goes through four individual layers before it is received on the other end. TCP/IP then goes through these layers in reverse order to reassemble the data and to present it to the recipient.

What is the internet?

The Internet is the backbone of the Web, the technical infrastructure that makes the Web possible. At its most basic, the Internet is a large network of computers which communicate all together.

What is UDP?

The User Datagram Protocol, or UDP, is a communication protocol used across the Internet for especially time-sensitive transmissions such as video playback or DNS lookups. It speeds up communications by not formally establishing a connection before data is transferred. This allows data to be transferred very quickly, but it can also cause packets to become lost in transit — and create opportunities for exploitation in the form of DDoS attacks.

What is the World Wide Web?

The World Wide Web, commonly known as the Web, is an information system where documents and other web resources are identified by Uniform Resource Locators (URLs), which may be interlinked by hyperlinks, and are accessible over the Internet.

Explain FTP.

The file transfer protocol or FTP is a widely used network protocol for transferring files between computers over a TCP/IP-based network, such as the Internet. FTP lets people and applications exchange and share data within their offices and across the Internet. FTP was one of the first technologies developed to solve this common need, and it remains, with several generations of enhancements, the second most popular protocol used today (after HTTP or the "World Wide Web").

How does the internet work?

The internet is made up of physical wires (optical fiber cables) that are buried in the ground that different servers can connect to. Web pages are files on the servers' hard drives. Every server has a unique internet protocol (IP) address. IP addresses help computers find each other similar to a postal address. Since IP addresses aren't very human friendly, the servers are also given domain names (e.g. google.com). Domain names and IP addresses are managed by ICANN, an organization based in the US. The internet uses the DNS (domain name system) to get the IP address that corresponds with the given domain name. A computer is not a server since it isn't directly connected to the internet. Computers are called clients because they connect to the internet indirectly through an internet service provider (ISP). When any type of data or information travels across the internet, computers break the data up into small pieces called packets which are basically just small chunks of binary (6 bits per packet). Packets also have a sequence number and hold onto the IP address of the destination. Packets aren't necessarily all sent along the same path, they all just take the best route available at that time. When the packets reach their destination, they are reassembled in their original order using the sequence number. Protocols are used to set the rules for packet conversion, attachment of the source and destination addresses, and the rules for routers. Different protocols are used for different applications. Any place that two or more parts of the internet intersect, there is a router. Routers direct packets around the internet.

What are the main components of a computer system?

The major hardware components of a computer system are: 1. Processor 2. Main memory 3. Secondary memory 4. Input devices 5. Output devices For typical desktop computers, the processor, main memory, secondary memory, power supply, and supporting hardware are housed in a metal case. Many of the components are connected to the main circuit board of the computer, called the motherboard. The power supply supplies power for most of the components. Various input devices (such as the keyboard) and output devices (such as the monitor) are attached through connectors at the rear of the case.

What is an operating system?

The most important systems program is the operating system. The operating system is always present when a computer is running. It coordinates the operation of the other hardware and software components of the computer system. The operating system is responsible for starting up application programs, running them, and managing the resources that they need. When an application program is running, the operating system manages the details of the hardware for it. For example, when you type characters on the keyboard, the operating system determines which application program they are intended for and does the work of getting them there.

Explain polymorphism.

The polymorphism is a core concept of an object-oriented paradigm that provides a way to perform a single action in different forms. It provides an ability to call the same method on different JavaScript objects.

What does the processor do?

The processor is an electronic device about a one inch square, covered in plastic. Inside the square is an even smaller square of silicon containing millions of tiny electrical parts. A modern processor may contain billions of transistors. It does the fundamental computing within the system, and directly or indirectly controls all the other components. The processor is sometimes called the Central Processing Unit or CPU. A particular computer will have a particular type of processor, such as a Pentium processor or a SPARC processor. The processor performs all the fundamental computation of the computer system. Other components contribute to the computation by doing such things as storing data or moving data into and out of the processor. But the processor is where the fundamental action takes place.

What are the two types of programs that can be run on a computer?

There are two categories of programs. Application programs (usually called just "applications") are programs that people use to get their work done. Computers exist because people want to run these programs. Systems programs keep the hardware and software running together smoothly. The difference between "application program" and "system program" is fuzzy. Often it is more a matter of marketing than of logic.