Computation is any type of calculation that includes both arithmetical and non-arithmetical steps and follows a well-defined model, for example an algorithm.
e-mail clientmail user agente-mail
When sending mail, users can only control encryption at the first hop from a client to its configured outgoing mail server. At any further hop, messages may be transmitted with or without encryption, depending solely on the general configuration of the transmitting server and the capabilities of the receiving one. Encrypted mail sessions deliver messages in their original format, i.e. plain text or encrypted body, on a user's local mailbox and on the destination server's. The latter server is operated by an email hosting service provider, possibly a different entity than the Internet access provider currently at hand.
Most high-end microprocessors (in desktop, laptop, server computers) have a memory management unit, translating logical addresses into physical RAM addresses, providing memory protection and paging abilities, useful for virtual memory. Simpler processors, especially microcontrollers, usually don't include an MMU. A CPU cache is a hardware cache used by the central processing unit (CPU) of a computer to reduce the average cost (time or energy) to access data from the main memory. A cache is a smaller, faster memory, closer to a processor core, which stores copies of the data from frequently used main memory locations.
Commonly reoccurring problems in the design and implementation of communication protocols can be addressed by patterns from several different pattern languages: Pattern Language for Application-level Communication Protocols ( CommDP), Service Design Patterns, Patterns of Enterprise Application Architecture, Pattern-Oriented Software Architecture: A Pattern Language for Distributed Computing. The first of these pattern languages focuses on the design of protocols and not their implementations. The others address issues in either both areas or just the latter.
For example, File Explorer (formerly Windows Explorer) is commonly used in Microsoft Windows operating systems, and Nautilus is common under several distributions of Linux. * Create a new file. Change the access permissions and attributes of a file. Open a file, which makes the file contents available to the program. Read data from a file. Write data to a file. Close a file, terminating the association between it and the program. The computer itself shutting down unexpectedly (for example, due to a power loss) with open files, or files in the process of being saved. A download being interrupted before it was completed. Due to a bad sector on the hard drive.
However, the similarly critical systems for actuating the brakes under driver control are inherently less robust, generally using a cable (can rust, stretch, jam, snap) or hydraulic fluid (can leak, boil and develop bubbles, absorb water and thus lose effectiveness).
virtual communitiesInternet communityonline community
The input box is where users can type their text-based message to be sent to the providing server. The server will then transmit the message to the computers of anyone in the chat room so that it can be displayed in the message window. The message window allows the conversation to be tracked and usually places a time stamp once the message is posted. There is usually a list of the users who are currently in the room, so that people can see who is in their virtual community. Users can communicate as if they are speaking to one another in real life.
financial crisis of 2007–2008global financial crisis2008 financial crisis
The distribution of household incomes in the United States has become more unequal during the post-2008 economic recovery, a first for the US but in line with the trend over the last ten economic recoveries since 1949. Income inequality in the United States has grown from 2005 to 2012 in more than 2 out of 3 metropolitan areas. Median household wealth fell 35% in the US, from $106,591 to $68,839 between 2005 and 2011.
computer scientistcomputer sciencescomputer scientists
When multiple computers are connected in a network while using concurrency, this is known as a distributed system. Computers within that distributed system have their own private memory, and information can be exchanged to achieve common goals. This branch of computer science aims to manage networks between computers worldwide. Computer security is a branch of computer technology with an objective of protecting information from unauthorized access, disruption, or modification while maintaining the accessibility and usability of the system for its intended users. Cryptography is the practice and study of hiding (encryption) and therefore deciphering (decryption) information.
Coase said that regardless of whether the judge ruled that the sweetmaker had to stop using his machinery, or that the doctor had to put up with it, they could strike a mutually beneficial bargain about who moves that reaches the same outcome of resource distribution. Only the existence of transaction costs may prevent this. So the law ought to pre-empt what would happen, and be guided by the most efficient solution. The idea is that law and regulation are not as important or effective at helping people as lawyers and government planners believe.
Coming at the end of the classical tradition, John Stuart Mill (1848) parted company with the earlier classical economists on the inevitability of the distribution of income produced by the market system. Mill pointed to a distinct difference between the market's two roles: allocation of resources and distribution of income. The market might be efficient in allocating resources but not in distributing income, he wrote, making it necessary for society to intervene. Value theory was important in classical theory. Smith wrote that the "real price of every thing ... is the toil and trouble of acquiring it".
After World War II, it was illegal in the US to sell or distribute encryption technology overseas; in fact, encryption was designated as auxiliary military equipment and put on the United States Munitions List. Until the development of the personal computer, asymmetric key algorithms (i.e., public key techniques), and the Internet, this was not especially problematic. However, as the Internet grew and computers became more widely available, high-quality encryption techniques became well known around the globe. In the 1990s, there were several challenges to US export regulation of cryptography.
public keypublic key cryptographyprivate key
Some certificate authority – usually a purpose-built program running on a server computer – vouches for the identities assigned to specific private keys by producing a digital certificate. Public key digital certificates are typically valid for several years at a time, so the associated private keys must be held securely over that time. When a private key used for certificate creation higher in the PKI server hierarchy is compromised, or accidentally disclosed, then a "man-in-the-middle attack" is possible, making any subordinate certificate wholly insecure.
It provides support for the development, promotion and distribution of European works within Europe and beyond. * * Official: Overviews and data: * News and interviews: * Der Spiegel interview with Helmut Schmidt and Valery Giscard d'Estaing Educational resources: * European Studies Hub – interactive learning tools and resources to help students and researchers better understand and engage with the European Union and its politics. the European Council, which sets the general political directions and priorities of the Union by gathering together its member states' heads of state/government (elected chief executives).
data backupback upbacked up
Backups provide a simple form of disaster recovery; however not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server. A backup system contains at least one copy of all data considered worth saving. The data storage requirements can be large. An information repository model may be used to provide structure to this storage. There are different types of data storage devices used for copying backups of data that is already in secondary storage onto archive files.
hardwarepersonal computer hardwaredevice
It can hold and store information both temporarily and permanently, and can be internal or external to a computer, server or any similar computing device. Data storage is a core function and fundamental component of computers. Data is stored by a computer using a variety of media. Hard disk drives are found in virtually all older computers, due to their high capacity and low cost, but solid-state drives are faster and more power efficient, although currently more expensive than hard drives in terms of dollar per gigabyte, so are often found in personal computers built post-2007. Some systems may use a disk array controller for greater performance or reliability.
open sourceopen-sourceopen source software
Some of the "more prominent organizations" involved in OSS development include the Apache Software Foundation, creators of the Apache web server; the Linux Foundation, a nonprofit which employed Linus Torvalds, the creator of the Linux operating system kernel; the Eclipse Foundation, home of the Eclipse software development platform; the Debian Project, creators of the influential Debian GNU/Linux distribution; the Mozilla Foundation, home of the Firefox web browser; and OW2, European-born community developing open source middleware. New organizations tend to have a more sophisticated governance model and their membership is often formed by legal entity members.
Roemer attempts to reformulate Marxist analysis to accommodate normative principles of distributive justice, shifting the argument for socialism away from purely technical and materialist reasons to one of distributive justice. Roemer argues that according to the principle of distributive justice, the traditional definition of socialism based on the principle that individual compensation be proportional to the value of the labour one expends in production is inadequate. Roemer concludes that egalitarians must reject socialism as it is classically defined in order for equality to be realized.
Sir Tim Berners-LeeTim Berners LeeTimothy Berners-Lee
His software also functioned as an editor (called WorldWideWeb, running on the NeXTSTEP operating system), and the first Web server, CERN HTTPd (short for Hypertext Transfer Protocol daemon). The first website was built at CERN. Despite this being an international organisation hosted by Switzerland, the office that Berners-Lee used was just across the border in France. The website was put online on 6 August 1991 for the first time: It provided an explanation of what the World Wide Web was, and how people could use a browser and set up a web server, as well as how to get started with your own website.
free and open-sourcefree and open source softwareFOSS
In the 1970s and early 1980s, some parts of the software industry began using technical measures (such as distributing only binary copies of computer programs) to prevent computer users from being able to use reverse engineering techniques to study and customize software they had paid for. In 1980, the copyright law was extended to computer programs in the United States —previously, computer programs could be considered ideas, procedures, methods, systems, and processes, which are not copyrightable. Early on, closed-source software was uncommon until the mid-1970s to the 1980s, when IBM implemented in 1983 an "object code only" policy, no longer distributing source code.
GossipGossip protocolsGossip-based membership protocol
Building low-diameter P2P networks. G. Pandurangan, P. Raghavan, Eli Upfal. In Proceedings of the 42nd Symposium on Foundations of Computer Science (FOCS), 2001. Astrolabe: A Robust and Scalable Technology for Distributed System Monitoring, Management, and Data Mining. Robbert van Renesse, Kenneth Birman and Werner Vogels. ACM Transactions on Computer Systems (TOCS) 21:2, May 2003. Exploiting Semantic Proximity in Peer-to-peer Content Searching. S. Voulgaris, A.-M. Kermarrec, L. Massoulie, M. van Steen. Proc. 10th Int'l Workshop on Future Trends in Distributed Computing Systems (FTDCS 2004), Suzhou, China, May 2004.
race conditionsdata racerace
In networking, consider a distributed chat network like IRC, where a user who starts a channel automatically acquires channel-operator privileges. If two users on different servers, on different ends of the same network, try to start the same-named channel at the same time, each user's respective server will grant channel-operator privileges to each user, since neither server will yet have received the other server's signal that it has allocated that channel. (This problem has been largely solved by various IRC server implementations.)
DNSresource recordDNS record
The Domain Name System is maintained by a distributed database system, which uses the client–server model. The nodes of this database are the name servers. Each domain has at least one authoritative DNS server that publishes information about that domain and the name servers of any domains subordinate to it. The top of the hierarchy is served by the root name servers, the servers to query when looking up (resolving) a TLD.
SkypingSkype PreviewJosh Silverman
Part of the Skype technology relies on the Global Index P2P protocol belonging to the Joltid Ltd. corporation. The main difference between Skype and standard VoIP clients is that Skype operates on a peer-to-peer model (originally based on the Kazaa software ), rather than the more usual client–server model (note that the very popular Session Initiation Protocol (SIP) model of VoIP is also peer-to-peer, but implementation generally requires registration with a server, as does Skype). On 20 June 2014, Microsoft announced the deprecation of the old Skype protocol.