Learn about each of them. Tsveti Georgieva on Feb 4, 2010 There are many web hosting offers on the market but actually more or less all of them can be classified into one of the following four categories: shared hosting, dedicated hosting, virtual private server (VPS) hosting, and reseller hosting. This article is a very brief overview of each of these four types, each of which is reviewed in more details into a separate article. In other words, many accounts and many sites per account can be hosted on one server independently of one another. The main advantage of shared hosting is that it is cheap. For many small and midsized sites a shared hosting package is the best deal but for a large site with heavy traffic shared hosting is generally insufficient. Dedicated Hosting Dedicated hosting is this type of a web hosting plan when a webmaster rents a whole server for his or her sites only. The prices of dedicated servers are very high (hundreds of dollars a month) and because of this dedicated servers are worth considering only when a site is a large one and there is a lot of traffic to it. One more benefit of dedicated hosting is that a webmaster has more freedom to choose the hardware, the operating system, and the other applications for the host. This is especially true for unmanaged web hosting because with this type of hosting the webmaster is the only one who administers the server. The second variety of a dedicated hosting package is managed hosting. Managed dedicated hosting means less freedom in administration for the webmaster because it is the hosting company who plays the main part in administering the server. VPS (Virtual Private Server) Hosting VPS hosting emerged recently when virtualization technologies made it possible to deploy multiple logical servers on one physical machine. With VPS each user has his or her virtual server, which is similar to dedicated hosting minus the price tag, but the virtual servers of many users reside on the same physical server, which bears some similarity to shared hosting. VPS hosting can be regarded as a cheaper surrogate of dedicated hosting or the more expensive (and powerful) counterpart of shared hosting. Reseller Hosting The fourth common type of web hosting plans, which is also the least popular, is reseller hosting . Reseller hosting can be regarded as a variety of dedicated hosting because when a webmaster signs up for a reseller hosting plan, he or she gets a dedicated server. However, the difference from dedicated hosting is that the webmaster can resell space on the server to third parties and make money in the process. The four types of web hosting plans are applicable in different situations. All of them can be used for business web hosting and it is mainly the size of the site (and the budget), which matter the most in the process of selection of one type of web hosting plan over the others. +
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Small stars host droves of life-friendly worlds
Courtney Dressing, an astronomer at Harvard University in Cambridge, Massachusetts, announced the results on 8 January at a meeting of the American Astronomical Society in Long Beach, California 1 . This is terrific, says Natalie Batalha, an astronomer at San Jose State University in California and deputy leader of the Kepler science team. Batalha chaired the meeting session at which Dressing presented the findings; at the end of the talk, Batalha was so stunned that she momentarily forgot to ask the audience for questions. The sweet spot Dressings study, done in collaboration with Harvard colleague David Charbonneau, focuses on the occurrence of planets that are Earth-sized which they define as having a radius between half and twice that of Earth and orbit so-called M dwarfs. These are cool, low-mass stars that account for about 75% of the stars in our Galaxy. In particular, the team looked for planets within the habitable zone, that is, whose orbits put them at the right distance from the star for water to exist in liquid state on their surfaces. Keplers main mission is to find the telltale dimming of larger, Sun-like stars caused when an orbiting planet crosses in front of or transits its star. However, the telescope also monitors stars of other types in its field of view. M dwarfs are relatively faint, so they are visible less often than other stars, despite their abundance. Among the roughly 150,000 stars that Kepler can observe and track, only 5,000 or so are M dwarfs. Kepler does not yet have enough data to estimate the occurrence of Earth-sized planets in the habitable zones of bright Sun-like stars. But Dressing realized that she could make such a calculation for M dwarfs, based on two facts. First, M dwarfs are relatively cool, so their habitable zones lie close to the star just less than Mercurys distance from the Sun. Planets with such narrow orbits make between five and seven transits each Earth year rather than the one of a planet in the habitable zone of a Sun-like star. The more-frequent transits provide more data for researchers. Second, because M dwarfs are relatively small, each transit blocks a greater proportion of their light, making the dimmings easier to detect. But before Dressing could perform her statistical analysis, she had to painstakingly review the radius and temperature of each M dwarf in the Kepler field of view. Previous, less accurate, estimates had been based on extrapolations from the study of Sun-like stars. Dressing and Charbonneau studied 3,609 M dwarfs out of the 5,000 in Keplers field of view and calculated that each of those has an 87% chance of harbouring an Earth-sized planet in an orbit of 50 days or less. That range includes planets in the habitable zone but also those that are closer to their star and therefore too hot. Their estimate is consistent with an independent calculation by John Johnson, an astronomer at the California Institute of Technology in Pasadena, and his colleagues, who also concluded that the Milky Way may contain as many as 100 billion planets in total. Johnson reported that result at the meeting on 7 January 2 . Near neighbours The Harvard astronomers estimate that 6% of the M dwarfs in Keplers field of view harbour Earth-sized planets in the habitable zone. That may not sound like much, notes Dressing, but given the preponderance of M dwarfs in the Galaxy, there should be at least one potentially habitable Earth-sized planet around an M dwarf within 20 light years of the Solar System. I hope that [Dressings] results garner a lot of attention at this meeting, because they are very profound and exciting, says Johnson. A different statistical analysis of Kepler data, reported on 7 January at the meeting 3 , considered the abundance of Earth-sized planets orbiting all stars not just M dwarfs with periods of 85 days or less. Francois Fressin, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, and his colleagues found that the Milky Way should contain about 17 billion Earth-sized planets, but not all of those would lie in the habitable zone. Charbonneau emphasizes that his team's findings are preliminary, and the researchers declined to discuss them in detail. But early last year, when the study had just begun, Charbonneau said that the final results could have an enormous impact on the study of exoplanets. If Earth-sized planets in the habitable zone are abundant in the nearby reaches of the Galaxy, they should be easily found by relatively small ground-based telescopes, such as the array that Charbonneaus team is now assembling at the Cerro Tololo Inter-American Observatory in Chile. Such planets would then be ideal candidates for study by NASA's James Webb Space Telescope, planned for launch in 2018.
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