Gigabit Ethernet
In computer networking, Gigabit Ethernet is the various technologies for transmitting Ethernet frames at a rate of a gigabit per second, as defined by the IEEE 802.3-2008 standard. It came into use beginning in 1999 supplanting Fast Ethernet in wired local networks, as a result of being faster; the cables and equipment are similar to previous standards and have been common and economical since 2010. Half-duplex gigabit links connected through repeater hubs were part of the IEEE specification, but the specification is not updated anymore and full-duplex operation with switches is used exclusively. Ethernet was the result of the research done at Xerox PARC in the early 1970s. Ethernet evolved into a implemented physical and link layer protocol. Fast Ethernet increased speed from 10 to 100 megabits per second. Gigabit Ethernet was the next iteration; the initial standard for Gigabit Ethernet was produced by the IEEE in June 1998 as IEEE 802.3z, required optical fiber. 802.3z is referred to as 1000BASE-X, where -X refers to either -CX, -SX, -LX, or -ZX.
For the history behind the "X" see Fast Ethernet. IEEE 802.3ab, ratified in 1999, defines Gigabit Ethernet transmission over unshielded twisted pair category 5, 5e or 6 cabling, became known as 1000BASE-T. With the ratification of 802.3ab, Gigabit Ethernet became a desktop technology as organizations could use their existing copper cabling infrastructure. IEEE 802.3ah, ratified in 2004 added two more gigabit fiber standards, 1000BASE-LX10 and 1000BASE-BX10. This was part of a larger group of protocols known as Ethernet in the First Mile. Gigabit Ethernet was deployed in high-capacity backbone network links. In 2000, Apple's Power Mac G4 and PowerBook G4 were the first mass-produced personal computers featuring the 1000BASE-T connection, it became a built-in feature in many other computers. There are five physical layer standards for Gigabit Ethernet using optical fiber, twisted pair cable, or shielded balanced copper cable; the IEEE 802.3z standard includes 1000BASE-SX for transmission over multi-mode fiber, 1000BASE-LX for transmission over single-mode fiber, the nearly obsolete 1000BASE-CX for transmission over shielded balanced copper cabling.
These standards use 8b/10b encoding, which inflates the line rate by 25%, from 1000 Mbit/s to 1250 Mbit/s, to ensure a DC balanced signal. The symbols are sent using NRZ. Optical fiber transceivers are most implemented as user-swappable modules in SFP form or GBIC on older devices. IEEE 802.3ab, which defines the used 1000BASE-T interface type, uses a different encoding scheme in order to keep the symbol rate as low as possible, allowing transmission over twisted pair. IEEE 802.3ap defines Ethernet Operation over Electrical Backplanes at different speeds. Ethernet in the First Mile added 1000BASE-LX10 and -BX10. 1000BASE-X is used in industry to refer to Gigabit Ethernet transmission over fiber, where options include 1000BASE-SX, 1000BASE-LX, 1000BASE-LX10, 1000BASE-BX10 or the non-standard -EX and -ZX implementations. Included are copper variants using the same 8b/10b line code. 1000BASE-CX is an initial standard for Gigabit Ethernet connections with maximum distances of 25 meters using balanced shielded twisted pair and either DE-9 or 8P8C connector.
The short segment length is due to high signal transmission rate. Although it is still used for specific applications where cabling is done by IT professionals, for instance the IBM BladeCenter uses 1000BASE-CX for the Ethernet connections between the blade servers and the switch modules, 1000BASE-T has succeeded it for general copper wiring use. 1000BASE-KX is part of the IEEE 802.3ap standard for Ethernet Operation over Electrical Backplanes. This standard defines one to four lanes of backplane links, one RX and one TX differential pair per lane, at link bandwidth ranging from 100Mbit to 10Gbit per second; the 1000BASE-KX variant uses 1.25 GBd electrical signalling speed. 1000BASE-SX is an optical fiber Gigabit Ethernet standard for operation over multi-mode fiber using a 770 to 860 nanometer, near infrared light wavelength. The standard specifies a maximum length of 220 meters for 62.5 µm/160 MHz×km multi-mode fiber, 275 m for 62.5 µm/200 MHz×km, 500 m for 50 µm/400MHz×km, 550 m for 50 µm/500 MHz×km multi-mode fiber.
In practice, with good quality fiber and terminations, 1000BASE-SX will work over longer distances. This standard is popular for intra-building links in large office buildings, co-location facilities and carrier-neutral Internet exchanges. Optical power specifications of SX interface: Minimum output power = −9.5 dBm. Minimum receive sensitivity = −17 dBm. 1000BASE-LX is an optical fiber Gigabit Ethernet standard specified in IEEE 802.3 Clause 38 which uses a long wavelength laser, a maximum RMS spectral width of 4 nm. 1000BASE-LX is specified to work over a distance of up to 5 km over 10 µm single-mode fiber. 1000BASE-LX can run over all common types of multi-mode fiber with a maximum segment length of 550 m. For link distances greater than 300 m, the use of a special launch conditioning patch cord may be required; this launches the laser at a precise offset from the center of the fiber which causes it to spread across the diameter of the fiber core, reducing the effect known as differential mode delay which occurs when the laser couples onto only a small number of available modes in multi-mode f
Computer hardware
Computer hardware includes the physical, tangible parts or components of a computer, such as the cabinet, central processing unit, keyboard, computer data storage, graphics card, sound card and motherboard. By contrast, software is instructions that can be run by hardware. Hardware is so-termed because it rigid with respect to changes or modifications. Intermediate between software and hardware is "firmware", software, coupled to the particular hardware of a computer system and thus the most difficult to change but among the most stable with respect to consistency of interface; the progression from levels of "hardness" to "softness" in computer systems parallels a progression of layers of abstraction in computing. Hardware is directed by the software to execute any command or instruction. A combination of hardware and software forms a usable computing system, although other systems exist with only hardware components; the template for all modern computers is the Von Neumann architecture, detailed in a 1945 paper by Hungarian mathematician John von Neumann.
This describes a design architecture for an electronic digital computer with subdivisions of a processing unit consisting of an arithmetic logic unit and processor registers, a control unit containing an instruction register and program counter, a memory to store both data and instructions, external mass storage, input and output mechanisms. The meaning of the term has evolved to mean a stored-program computer in which an instruction fetch and a data operation cannot occur at the same time because they share a common bus; this is referred to as the Von Neumann bottleneck and limits the performance of the system. The personal computer known as the PC, is one of the most common types of computer due to its versatility and low price. Laptops are very similar, although they may use lower-power or reduced size components, thus lower performance; the computer case encloses most of the components of the system. It provides mechanical support and protection for internal elements such as the motherboard, disk drives, power supplies, controls and directs the flow of cooling air over internal components.
The case is part of the system to control electromagnetic interference radiated by the computer, protects internal parts from electrostatic discharge. Large tower cases provide extra internal space for multiple disk drives or other peripherals and stand on the floor, while desktop cases provide less expansion room. All-in-one style designs include a video display built into the same case. Portable and laptop computers require cases. A current development in laptop computers is a detachable keyboard, which allows the system to be configured as a touch-screen tablet. Hobbyists may decorate the cases with colored lights, paint, or other features, in an activity called case modding. A power supply unit converts alternating current electric power to low-voltage DC power for the internal components of the computer. Laptops are capable of running from a built-in battery for a period of hours; the motherboard is the main component of a computer. It is a board with integrated circuitry that connects the other parts of the computer including the CPU, the RAM, the disk drives as well as any peripherals connected via the ports or the expansion slots.
Components directly attached to or to part of the motherboard include: The CPU, which performs most of the calculations which enable a computer to function, is sometimes referred to as the brain of the computer. It is cooled by a heatsink and fan, or water-cooling system. Most newer CPUs include an on-die graphics processing unit; the clock speed of CPUs governs how fast it executes instructions, is measured in GHz. Many modern computers have the option to overclock the CPU which enhances performance at the expense of greater thermal output and thus a need for improved cooling; the chipset, which includes the north bridge, mediates communication between the CPU and the other components of the system, including main memory. Random-access memory, which stores the code and data that are being accessed by the CPU. For example, when a web browser is opened on the computer it takes up memory. RAM comes on DIMMs in the sizes 2GB, 4GB, 8GB, but can be much larger. Read-only memory, which stores the BIOS that runs when the computer is powered on or otherwise begins execution, a process known as Bootstrapping, or "booting" or "booting up".
The BIOS includes power management firmware. Newer motherboards use Unified Extensible Firmware Interface instead of BIOS. Buses that connect the CPU to various internal components and to expand cards for graphics and sound; the CMOS battery, which powers the memory for date and time in the BIOS chip. This battery is a watch battery; the video card, which processes computer graphics. More powerful graphics cards are better suited to handle strenuous tasks, such as playing intensive video games. An expansion card in computing is a printed circuit board that can be inserted into an expansion slot of a computer motherboard or
Ethernet
Ethernet is a family of computer networking technologies used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3, has since retained a good deal of backward compatibility and been refined to support higher bit rates and longer link distances. Over time, Ethernet has replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET; the original 10BASE5 Ethernet uses coaxial cable as a shared medium, while the newer Ethernet variants use twisted pair and fiber optic links in conjunction with switches. Over the course of its history, Ethernet data transfer rates have been increased from the original 2.94 megabits per second to the latest 400 gigabits per second. The Ethernet standards comprise several wiring and signaling variants of the OSI physical layer in use with Ethernet. Systems communicating over Ethernet divide a stream of data into shorter pieces called frames; each frame contains source and destination addresses, error-checking data so that damaged frames can be detected and discarded.
As per the OSI model, Ethernet provides services up including the data link layer. Features such as the 48-bit MAC address and Ethernet frame format have influenced other networking protocols including Wi-Fi wireless networking technology. Ethernet is used in home and industry; the Internet Protocol is carried over Ethernet and so it is considered one of the key technologies that make up the Internet. Ethernet was developed at Xerox PARC between 1973 and 1974, it was inspired by ALOHAnet. The idea was first documented in a memo that Metcalfe wrote on May 22, 1973, where he named it after the luminiferous aether once postulated to exist as an "omnipresent, completely-passive medium for the propagation of electromagnetic waves." In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker, Butler Lampson as inventors. In 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper; that same year, Ron Crane, Bob Garner, Roy Ogus facilitated the upgrade from the original 2.94 Mbit/s protocol to the 10 Mbit/s protocol, released to the market in 1980.
Metcalfe left Xerox in June 1979 to form 3Com. He convinced Digital Equipment Corporation and Xerox to work together to promote Ethernet as a standard; as part of that process Xerox agreed to relinquish their'Ethernet' trademark. The first standard was published on September 1980 as "The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications"; this so-called DIX standard specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and a global 16-bit Ethertype-type field. Version 2 was published in November, 1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the same time and resulted in the publication of IEEE 802.3 on June 23, 1983. Ethernet competed with Token Ring and other proprietary protocols. Ethernet was able to adapt to market realities and shift to inexpensive thin coaxial cable and ubiquitous twisted pair wiring. By the end of the 1980s, Ethernet was the dominant network technology. In the process, 3Com became a major company.
3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, that year started selling adapters for PDP-11s and VAXes, as well as Multibus-based Intel and Sun Microsystems computers. This was followed by DEC's Unibus to Ethernet adapter, which DEC sold and used internally to build its own corporate network, which reached over 10,000 nodes by 1986, making it one of the largest computer networks in the world at that time. An Ethernet adapter card for the IBM PC was released in 1982, and, by 1985, 3Com had sold 100,000. Parallel port based Ethernet adapters were produced with drivers for DOS and Windows. By the early 1990s, Ethernet became so prevalent that it was a must-have feature for modern computers, Ethernet ports began to appear on some PCs and most workstations; this process was sped up with the introduction of 10BASE-T and its small modular connector, at which point Ethernet ports appeared on low-end motherboards. Since Ethernet technology has evolved to meet new bandwidth and market requirements.
In addition to computers, Ethernet is now used to interconnect appliances and other personal devices. As Industrial Ethernet it is used in industrial applications and is replacing legacy data transmission systems in the world's telecommunications networks. By 2010, the market for Ethernet equipment amounted to over $16 billion per year. In February 1980, the Institute of Electrical and Electronics Engineers started project 802 to standardize local area networks; the "DIX-group" with Gary Robinson, Phil Arst, Bob Printis submitted the so-called "Blue Book" CSMA/CD specification as a candidate for the LAN specification. In addition to CSMA/CD, Token Ring and Token Bus were considered as candidates for a LAN standard. Competing proposals and broad interest in the initiative led to strong disagreement over which technology to standardize. In December 1980, the group was split into three subgroups, standardization proceeded separately for each proposal. Delays in the standards process put at risk the market introduction of the Xerox Star workstation and 3Com's Ethernet LAN products.
With such business implications in mind, David Liddle an
10 Gigabit Ethernet
10 Gigabit Ethernet is a group of computer networking technologies for transmitting Ethernet frames at a rate of 10 gigabits per second. It was first defined by the IEEE 802.3ae-2002 standard. Unlike previous Ethernet standards, 10 Gigabit Ethernet defines only full-duplex point-to-point links which are connected by network switches; the 10 Gigabit Ethernet standard encompasses a number of different physical layer standards. A networking device, such as a switch or a network interface controller may have different PHY types through pluggable PHY modules, such as those based on SFP+. Like previous versions of Ethernet, 10GbE can use either fiber cabling. Maximum distance over copper cable is 100 meters but because of its bandwidth requirements, higher-grade cables are required; the adoption of 10 Gigabit Ethernet has been more gradual than previous revisions of Ethernet: in 2007, one million 10GbE ports were shipped, in 2009 two million ports were shipped, in 2010 over three million ports were shipped, with an estimated nine million ports in 2011.
As of 2012, although the price per gigabit of bandwidth for 10 Gigabit Ethernet was about one-third compared to Gigabit Ethernet, the price per port of 10 Gigabit Ethernet still hindered more widespread adoption. Over the years the Institute of Electrical and Electronics Engineers 802.3 working group has published several standards relating to 10GbE. To implement different 10GbE physical layer standards, many interfaces consist of a standard socket into which different PHY modules may be plugged. Physical layer modules are not specified in an official standards body but by multi-source agreements that can be negotiated more quickly. Relevant MSAs for 10GbE include XENPAK, XFP and SFP+; when choosing a PHY module, a designer considers cost, media type, power consumption, size. A single point-to-point link can have different MSA pluggable formats on either end as long as the 10GbE optical or copper port type supported by the pluggable is identical. XENPAK had the largest form factor. X2 and XPAK were competing standards with smaller form factors.
X2 and XPAK have not been as successful in the market as XENPAK. XFP came after X2 and XPAK and it is smaller; the newest module standard is the enhanced small form-factor pluggable transceiver called SFP+. Based on the small form-factor pluggable transceiver and developed by the ANSI T11 fibre channel group, it is smaller still and lower power than XFP. SFP+ has become the most popular socket on 10GE systems. SFP+ modules do only optical to electrical conversion, no clock and data recovery, putting a higher burden on the host's channel equalization. SFP+ modules share a common physical form factor with legacy SFP modules, allowing higher port density than XFP and the re-use of existing designs for 24 or 48 ports in a 19-inch rack width blade. Optical modules are connected to a host by either a XFI or SerDes Framer Interface interface. XENPAK, X2, XPAK modules use XAUI to connect to their hosts. XAUI uses a four-lane data channel and is specified in IEEE 802.3 Clause 47. XFP modules use a XFI SFP + modules use an SFI interface.
XFI and SFI use a single lane data channel and the 64b/66b encoding specified in IEEE 802.3 Clause 49. SFP+ modules can further be grouped into two types of host interfaces: linear or limiting. Limiting modules are preferred for long-reach applications using 10GBASE-LRM modules. There are two basic types of optical fiber used for 10 Gigabit Ethernet: multi-mode. In SMF light follows a single path through the fiber while in MMF it takes multiple paths resulting in differential mode delay. SMF is used for long distance communication and MMF is used for distances of less than 300 m. SMF has a narrower core which requires a more precise termination and connection method. MMF has a wider core; the advantage of MMF is that it can be driven by a low cost Vertical-cavity surface-emitting laser for short distances, multi-mode connectors are cheaper and easier to terminate reliably in the field. The advantage of SMF is. In the 802.3 standard, reference is made to FDDI-grade MMF fiber. This has a minimum modal bandwidth of 160 MHz · km at 850 nm.
It was installed in the early 1990s for FDDI and 100BASE-FX networks. The 802.3 standard references ISO/IEC 11801 which specifies optical MMF fiber types OM1, OM2, OM3 and OM4. OM1 has a 62.5 µm core. At 850 nm the minimum modal bandwidth of OM1 is 200 MHz·km, of OM2 500 MHz·km, of OM3 2000 MHz·km and of OM4 4700 MHz·km. FDDI-grade cable is now obsolete and new structured cabling installations use either OM3 or OM4 cabling. OM3 cable can carry 10 Gigabit Ethernet 300 meters using low cost 10GBASE-SR optics. OM4 can manage 400 meters. To distinguish SMF from MMF cables, SMF cables are yellow, while MMF cables are orange or aqua. However, in fiber optics there is no uniform color for any specific optical speed or technology with the exception being angular physical connector, it being an agreed color of green. There are active optical cables; these have the optical electronics connected eliminating the connectors between the cable and the optical module. They plug into standard SFP+ sockets, they are lower cost than other optical solutions because the manufacturer can match the electronics t
Computer network
A computer network is a digital telecommunications network which allows nodes to share resources. In computer networks, computing devices exchange data with each other using connections between nodes; these data links are established over cable media such as wires or optic cables, or wireless media such as Wi-Fi. Network computer devices that originate and terminate the data are called network nodes. Nodes are identified by network addresses, can include hosts such as personal computers and servers, as well as networking hardware such as routers and switches. Two such devices can be said to be networked together when one device is able to exchange information with the other device, whether or not they have a direct connection to each other. In most cases, application-specific communications protocols are layered over other more general communications protocols; this formidable collection of information technology requires skilled network management to keep it all running reliably. Computer networks support an enormous number of applications and services such as access to the World Wide Web, digital video, digital audio, shared use of application and storage servers and fax machines, use of email and instant messaging applications as well as many others.
Computer networks differ in the transmission medium used to carry their signals, communications protocols to organize network traffic, the network's size, traffic control mechanism and organizational intent. The best-known computer network is the Internet; the chronology of significant computer-network developments includes: In the late 1950s, early networks of computers included the U. S. military radar system Semi-Automatic Ground Environment. In 1959, Anatolii Ivanovich Kitov proposed to the Central Committee of the Communist Party of the Soviet Union a detailed plan for the re-organisation of the control of the Soviet armed forces and of the Soviet economy on the basis of a network of computing centres, the OGAS. In 1960, the commercial airline reservation system semi-automatic business research environment went online with two connected mainframes. In 1963, J. C. R. Licklider sent a memorandum to office colleagues discussing the concept of the "Intergalactic Computer Network", a computer network intended to allow general communications among computer users.
In 1964, researchers at Dartmouth College developed the Dartmouth Time Sharing System for distributed users of large computer systems. The same year, at Massachusetts Institute of Technology, a research group supported by General Electric and Bell Labs used a computer to route and manage telephone connections. Throughout the 1960s, Paul Baran and Donald Davies independently developed the concept of packet switching to transfer information between computers over a network. Davies pioneered the implementation of the concept with the NPL network, a local area network at the National Physical Laboratory using a line speed of 768 kbit/s. In 1965, Western Electric introduced the first used telephone switch that implemented true computer control. In 1966, Thomas Marill and Lawrence G. Roberts published a paper on an experimental wide area network for computer time sharing. In 1969, the first four nodes of the ARPANET were connected using 50 kbit/s circuits between the University of California at Los Angeles, the Stanford Research Institute, the University of California at Santa Barbara, the University of Utah.
Leonard Kleinrock carried out theoretical work to model the performance of packet-switched networks, which underpinned the development of the ARPANET. His theoretical work on hierarchical routing in the late 1970s with student Farouk Kamoun remains critical to the operation of the Internet today. In 1972, commercial services using X.25 were deployed, used as an underlying infrastructure for expanding TCP/IP networks. In 1973, the French CYCLADES network was the first to make the hosts responsible for the reliable delivery of data, rather than this being a centralized service of the network itself. In 1973, Robert Metcalfe wrote a formal memo at Xerox PARC describing Ethernet, a networking system, based on the Aloha network, developed in the 1960s by Norman Abramson and colleagues at the University of Hawaii. In July 1976, Robert Metcalfe and David Boggs published their paper "Ethernet: Distributed Packet Switching for Local Computer Networks" and collaborated on several patents received in 1977 and 1978.
In 1979, Robert Metcalfe pursued making Ethernet an open standard. In 1976, John Murphy of Datapoint Corporation created ARCNET, a token-passing network first used to share storage devices. In 1995, the transmission speed capacity for Ethernet increased from 10 Mbit/s to 100 Mbit/s. By 1998, Ethernet supported transmission speeds of a Gigabit. Subsequently, higher speeds of up to 400 Gbit/s were added; the ability of Ethernet to scale is a contributing factor to its continued use. Computer networking may be considered a branch of electrical engineering, electronics engineering, telecommunications, computer science, information technology or computer engineering, since it relies upon the theoretical and practical application of the related disciplines. A computer network facilitates interpersonal communications allowing users to communicate efficiently and via various means: email, instant messaging, online chat, video telephone calls, video conferencing. A network allows sharing of computing resources.
Users may access and use resources provided by devices on the network, such as printing a document on a shared network printer or use of a shared storage device. A network allows sharing of files, and
Fast Ethernet
In computer networking, Fast Ethernet physical layers carry traffic at the nominal rate of 100 Mbit/s. The prior Ethernet speed was 10 Mbit/s. Of the Fast Ethernet physical layers, 100BASE-TX is by far the most common. Fast Ethernet was introduced in 1995 as the IEEE 802.3u standard and remained the fastest version of Ethernet for three years before the introduction of Gigabit Ethernet. The acronym GE/FE is sometimes used for devices supporting both standards; the "100" in the media type designation refers to the transmission speed of 100 Mbit/s, while the "BASE" refers to baseband signalling. The letter following the dash refers to the physical medium that carries the signal, while the last character refers to the line code method used. Fast Ethernet is sometimes referred to as 100BASE-X, where "X" is a placeholder for the FX and TX variants. Fast Ethernet is an extension of the 10 megabit Ethernet standard, it runs on twisted pair or optical fiber cable in a star wired bus topology, similar to the IEEE standard 802.3i called 10BASE-T, itself an evolution of 10BASE5 and 10BASE2.
Fast Ethernet devices are backward compatible with existing 10BASE-T systems, enabling plug-and-play upgrades from 10BASE-T. Most switches and other networking devices with ports capable of Fast Ethernet can perform autonegotiation, sensing a piece of 10BASE-T equipment and setting the port to 10BASE-T half duplex if the 10BASE-T equipment cannot perform auto negotiation itself; the standard specifies the use of CSMA/CD for media access control. A full-duplex mode is specified and in practice all modern networks use Ethernet switches and operate in full-duplex mode as legacy devices that use half duplex still exist. A Fast Ethernet adapter can be logically divided into a media access controller, which deals with the higher-level issues of medium availability, a physical layer interface; the MAC is linked to the PHY by a four-bit 25 MHz synchronous parallel interface known as a media-independent interface, or by a two-bit 50 MHz variant called reduced media independent interface. In rare cases the MII may be an external connection but is a connection between ICs in a network adapter or two sections within a single IC.
The specs are written based on the assumption that the interface between MAC and PHY will be an MII but they do not require it. Fast Ethernet or Ethernet hubs may use the MII to connect to multiple PHYs for their different interfaces; the MII fixes the theoretical maximum data bit rate for all versions of Fast Ethernet to 100 Mbit/s. The information rate observed on real networks is less than the theoretical maximum, due to the necessary header and trailer on every Ethernet frame, the required interpacket gap between transmissions. 100BASE-T is any of several Fast Ethernet standards for twisted pair cables, including: 100BASE-TX, 100BASE-T4, 100BASE-T2. The segment length for a 100BASE-T cable is limited to 100 metres. All are or were standards under IEEE 802.3. All 100BASE-T installations are 100BASE-TX. 100BASE-TX is the predominant form of Fast Ethernet, runs over two wire-pairs inside a category 5 or above cable. Each network segment can have a maximum cabling distance of 100 metres. One pair is used for each direction, providing full-duplex operation with 100 Mbit/s of throughput in each direction.
Like 10BASE-T, the active pairs in a standard connection are terminated on pins 1, 2, 3 and 6. Since a typical category 5 cable contains 4 pairs, it can support two 100BASE-TX links with a wiring adaptor. Cabling is conventional wired to TIA/EIA-568-B's termination standards, T568A or T568B; this places the active pairs on the green pairs. The configuration of 100BASE-TX networks is similar to 10BASE-T; when used to build a local area network, the devices on the network are connected to a hub or switch, creating a star network. Alternatively it is possible to connect two devices directly using a crossover cable. With today's equipment, crossover cables are not needed as most equipment support auto-negotiation along with auto MDI-X to select and match speed and pairing. With 100BASE-TX hardware, the raw bits, presented 4 bits wide clocked at 25 MHz at the MII, go through 4B5B binary encoding to generate a series of 0 and 1 symbols clocked at a 125 MHz symbol rate; the 4B5B encoding provides DC spectrum shaping.
Just as in the 100BASE-FX case, the bits are transferred to the physical medium attachment layer using NRZI encoding. However, 100BASE-TX introduces an additional, medium dependent sublayer, which employs MLT-3 as a final encoding of the data stream before transmission, resulting in a maximum fundamental frequency of 31.25 MHz. The procedure is borrowed with minor changes. 100BASE-T4 was an early implementation of Fast Ethernet. It requires four twisted copper pairs of voice grade twisted pair, a lower performing cable compared to category 5 cable used by 1000BASE-TX. Maximum distance is limited to 100 meters. One pair is reserved for transmit, one for receive, the remaining two switch direction; the fact that 3 pairs are used to transmit in each direction makes 100BASE-T4 inherently half-duplex. A unusual 8B6T code is used to convert 8 data bits into 6 base-3 digits (the signal shaping is possible as there are nearly three times as many 6-digit base-3 n
Apple Inc.
Apple Inc. is an American multinational technology company headquartered in Cupertino, that designs and sells consumer electronics, computer software, online services. It is considered one of the Big Four of technology along with Amazon and Facebook; the company's hardware products include the iPhone smartphone, the iPad tablet computer, the Mac personal computer, the iPod portable media player, the Apple Watch smartwatch, the Apple TV digital media player, the HomePod smart speaker. Apple's software includes the macOS and iOS operating systems, the iTunes media player, the Safari web browser, the iLife and iWork creativity and productivity suites, as well as professional applications like Final Cut Pro, Logic Pro, Xcode, its online services include the iTunes Store, the iOS App Store, Mac App Store, Apple Music, Apple TV+, iMessage, iCloud. Other services include Apple Store, Genius Bar, AppleCare, Apple Pay, Apple Pay Cash, Apple Card. Apple was founded by Steve Jobs, Steve Wozniak, Ronald Wayne in April 1976 to develop and sell Wozniak's Apple I personal computer, though Wayne sold his share back within 12 days.
It was incorporated as Apple Computer, Inc. in January 1977, sales of its computers, including the Apple II, grew quickly. Within a few years and Wozniak had hired a staff of computer designers and had a production line. Apple went public in 1980 to instant financial success. Over the next few years, Apple shipped new computers featuring innovative graphical user interfaces, such as the original Macintosh in 1984, Apple's marketing advertisements for its products received widespread critical acclaim. However, the high price of its products and limited application library caused problems, as did power struggles between executives. In 1985, Wozniak departed Apple amicably and remained an honorary employee, while Jobs and others resigned to found NeXT; as the market for personal computers expanded and evolved through the 1990s, Apple lost market share to the lower-priced duopoly of Microsoft Windows on Intel PC clones. The board recruited CEO Gil Amelio to what would be a 500-day charge for him to rehabilitate the financially troubled company—reshaping it with layoffs, executive restructuring, product focus.
In 1997, he led Apple to buy NeXT, solving the failed operating system strategy and bringing Jobs back. Jobs pensively regained leadership status, becoming CEO in 2000. Apple swiftly returned to profitability under the revitalizing Think different campaign, as he rebuilt Apple's status by launching the iMac in 1998, opening the retail chain of Apple Stores in 2001, acquiring numerous companies to broaden the software portfolio. In January 2007, Jobs renamed the company Apple Inc. reflecting its shifted focus toward consumer electronics, launched the iPhone to great critical acclaim and financial success. In August 2011, Jobs resigned as CEO due to health complications, Tim Cook became the new CEO. Two months Jobs died, marking the end of an era for the company. Apple is well known for its size and revenues, its worldwide annual revenue totaled $265 billion for the 2018 fiscal year. Apple is the world's largest information technology company by revenue and the world's third-largest mobile phone manufacturer after Samsung and Huawei.
In August 2018, Apple became the first public U. S. company to be valued at over $1 trillion. The company employs 123,000 full-time employees and maintains 504 retail stores in 24 countries as of 2018, it operates the iTunes Store, the world's largest music retailer. As of January 2018, more than 1.3 billion Apple products are in use worldwide. The company has a high level of brand loyalty and is ranked as the world's most valuable brand. However, Apple receives significant criticism regarding the labor practices of its contractors, its environmental practices and unethical business practices, including anti-competitive behavior, as well as the origins of source materials. Apple Computer Company was founded on April 1, 1976, by Steve Jobs, Steve Wozniak, Ronald Wayne; the company's first product is the Apple I, a computer designed and hand-built by Wozniak, first shown to the public at the Homebrew Computer Club. Apple I was sold as a motherboard —a base kit concept which would now not be marketed as a complete personal computer.
The Apple I went on sale in July 1976 and was market-priced at $666.66. Apple Computer, Inc. was incorporated on January 3, 1977, without Wayne, who had left and sold his share of the company back to Jobs and Wozniak for $800 only twelve days after having co-founded Apple. Multimillionaire Mike Markkula provided essential business expertise and funding of $250,000 during the incorporation of Apple. During the first five years of operations revenues grew exponentially, doubling about every four months. Between September 1977 and September 1980, yearly sales grew from $775,000 to $118 million, an average annual growth rate of 533%; the Apple II invented by Wozniak, was introduced on April 16, 1977, at the first West Coast Computer Faire. It differs from its major rivals, the TRS-80 and Commodore PET, because of its character cell-based color graphics and open architecture. While early Apple II models use ordinary cassette tapes as storage devices, they were superseded by the introduction of a 5 1⁄4-inch floppy disk drive and interface called the Disk II.
The Apple II was chosen to be the desktop platform for the first "killer app" of the business world: VisiCalc, a spreadsheet program. VisiCalc created a business market for the Apple II and gave home users an additional reason to buy an Apple II: compatibility with the office. Before VisiCalc, Apple had been a distant third place c
