Norma Arm

The Norma Arm is a minor spiral arm of the Milky Way extending from and around its central hub region. The inner portion of the Arm is called Norma Arm in narrow meaning. The outer part of it is identified either with Cygnus Arm, which lies outside the Perseus Arm, or Outer Arm, which is located further away from the center of the Galaxy than Cygnus Arm. Norma Arm has a radius of 15.5 ± 2.8 kpc. It is named for the Norma constellation, through which the Arm as seen from Earth passes.

Like many other galaxies of similar type, the Milky Way consists of a large mass of stars shaped into the form of a relatively flat disc by gravity. The disc is rotating, with the dense central body of stars moving at greater speeds than those towards the rim of the disc. As a result, the pattern of stars within the Galaxy as viewed from directly above or below the disc has formed into a spiral.

Because of localised gravitational variations, the spiral pattern has itself formed several distinct 'spiral arms', where particularly large numbers of stars can be found.

Norma

Norma may refer to:

In science and technology:

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Other uses:

Norma (constellation)

Norma is a small constellation in the Southern Celestial Hemisphere between Scorpius and Centaurus, one of twelve drawn up in the 18th century by French astronomer Nicolas Louis de Lacaille and one of several depicting scientific instruments. Its name is Latin for normal, referring to a right angle, and is variously considered to represent a rule, a carpenter's square, a set square or a level.

Four of Norma's brighter stars—Gamma, Delta, Epsilon and Eta—make up a square in the field of faint stars. Gamma² Normae is the brightest star with an apparent magnitude of 4.0. Mu Normae is one of the most luminous stars known, with a luminosity half- to one million times that of the Sun. Four star systems are known to harbour planets. The Milky Way passes through Norma, and the constellation contains eight open clusters visible to observers with binoculars. The constellation also hosts Abell 3627, also called the Norma Cluster, one of the most massive galaxy clusters known.

History

Norma, Lazio

Norma is a comune (municipality) in the Province of Latina in the Italian region Lazio, located about 50 kilometres (31 mi) southeast of Rome and about 14 kilometres (9 mi) northeast of Latina in the Monti Lepini range.

Its territory houses the Gardens of Ninfa. A summer camp was held there once.

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External links

Tor (anonymity network)

Tor is free software for enabling anonymous communication. The name is an acronym derived from the original software project name The Onion Router, however the correct spelling is "Tor", capitalizing only the first letter. Tor directs Internet traffic through a free, worldwide, volunteer network consisting of more than seven thousand relays to conceal a user's location and usage from anyone conducting network surveillance or traffic analysis. Using Tor makes it more difficult for Internet activity to be traced back to the user: this includes "visits to Web sites, online posts, instant messages, and other communication forms". Tor's use is intended to protect the personal privacy of users, as well as their freedom and ability to conduct confidential communication by keeping their Internet activities from being monitored.

Onion routing is implemented by encryption in the application layer of a communication protocol stack, nested like the layers of an onion. Tor encrypts the data, including the destination IP address, multiple times and sends it through a virtual circuit comprising successive, randomly selected Tor relays. Each relay decrypts a layer of encryption to reveal only the next relay in the circuit in order to pass the remaining encrypted data on to it. The final relay decrypts the innermost layer of encryption and sends the original data to its destination without revealing, or even knowing, the source IP address. Because the routing of the communication is partly concealed at every hop in the Tor circuit, this method eliminates any single point at which the communicating peers can be determined through network surveillance that relies upon knowing its source and destination.

ARM9

ARM9 is a group of older 32-bit RISC ARM processor cores licensed by ARM Holdings.

Overview

With this design generation, ARM moved from a von Neumann architecture (Princeton architecture) to a Harvard architecture with separate instruction and data buses (and caches), significantly increasing its potential speed. Most silicon chips integrating these cores will package them as modified Harvard architecture chips, combining the two address buses on the other side of separated CPU caches and tightly coupled memories.

There are two subfamilies, implementing different ARM architecture versions.

Differences from ARM7 cores

Key improvements over ARM7 cores, enabled by spending more transistors, include:

List of ARM microarchitectures

This is a list of microarchitectures based on the ARM family of instruction sets designed by ARM Holdings and 3rd parties, sorted by version of the ARM instruction set, release and name. ARM provides a summary of the numerous vendors who implement ARM cores in their design.Keil also provides a somewhat newer summary of vendors of ARM based processors. ARM further provides a chart displaying an overview of the ARM processor lineup with performance and functionality versus capabilities for the more recent ARM core families.

ARM cores

Designed by ARM

Designed by third parties

These cores implement the ARM instruction set, and were developed independently by companies with an architectural license from ARM.

ARM core timeline

The following table lists each core by the year it was announced.

See also

References

Further reading