1.
Conventional PCI
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Conventional PCI, often shortened to PCI, is a local computer bus for attaching hardware devices in a computer. PCI is the initialism for Peripheral Component Interconnect and is part of the PCI Local Bus standard, the PCI bus supports the functions found on a processor bus but in a standardized format that is independent of any particular processors native bus. Devices connected to the PCI bus appear to a bus master to be connected directly to its own bus and are assigned addresses in the address space. It is a bus, synchronous to a single bus clock. Attached devices can take either the form of an integrated circuit fitted onto the motherboard itself or a card that fits into a slot. The PCI Local Bus was first implemented in IBM PC compatibles and it has subsequently been adopted for other computer types. Typical PCI cards used in PCs include, network cards, sound cards, modems, extra ports such as USB or serial, TV tuner cards, PCI video cards replaced ISA and VESA cards until growing bandwidth requirements outgrew the capabilities of PCI. The preferred interface for video cards then became AGP, itself a superset of conventional PCI and these have one locating notch in the card. Version 2.0 of the PCI standard introduced 3.3 V slots, universal cards, which can operate on either voltage, have two notches. Version 2.1 of the PCI standard introduced optional 66 MHz operation, a server-oriented variant of conventional PCI, called PCI-X operated at frequencies up to 133 MHz for PCI-X1.0 and up to 533 MHz for PCI-X2.0. An internal connector for laptop cards, called Mini PCI, was introduced in version 2.2 of the PCI specification, the PCI bus was also adopted for an external laptop connector standard – the CardBus. The first PCI specification was developed by Intel, but subsequent development of the standard became the responsibility of the PCI Special Interest Group, Conventional PCIs heyday in the desktop computer market was approximately 1995–2005. PCI and PCI-X have become obsolete for most purposes, however, they are common on modern desktops for the purposes of backwards compatibility. Many kinds of devices available on PCI expansion cards are now commonly integrated onto motherboards or available in USB. Work on PCI began at Intels Architecture Development Lab c. 1990, a team of Intel engineers defined the architecture and developed a proof of concept chipset and platform partnering with teams in the companys desktop PC systems and core logic product organizations. PCI was immediately put to use in servers, replacing MCA, in mainstream PCs, PCI was slower to replace VESA Local Bus, and did not gain significant market penetration until late 1994 in second-generation Pentium PCs. By 1996, VLB was all but extinct, and manufacturers had adopted PCI even for 486 computers, EISA continued to be used alongside PCI through 2000. Apple Computer adopted PCI for professional Power Macintosh computers in mid-1995, the 64-bit version of plain PCI remained rare in practice though, although it was used for example by all G3 and G4 Power Macintosh computers
2.
Network interface controller
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A network interface controller is a computer hardware component that connects a computer to a computer network. Early network interface controllers were commonly implemented on expansion cards that plugged into a computer bus, the low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the motherboard. The network controller implements the electronic circuitry required to communicate using a physical layer and data link layer standard such as Ethernet, Fibre Channel. The NIC allows computers to communicate over a network, either by using cables or wirelessly. Although other network technologies exist, IEEE802 networks including the Ethernet variants have achieved near-ubiquity since the mid-1990s, newer server motherboards may even have dual network interfaces built-in. The Ethernet capabilities are integrated into the motherboard chipset or implemented via a low-cost dedicated Ethernet chip. A separate network card is not required unless additional interfaces are needed or some type of network is used. The NIC may use one or more of the techniques to indicate the availability of packets to transfer. Interrupt-driven I/O is where the peripheral alerts the CPU that it is ready to transfer data, also, NICs may use one or more of the following techniques to transfer packet data, Programmed input/output is where the CPU moves the data to or from the NIC to memory. Direct memory access is where some other device other than the CPU assumes control of the bus to move data to or from the NIC to memory. This removes load from the CPU but requires more logic on the card, in addition, a packet buffer on the NIC may not be required and latency can be reduced. There are two types of DMA, third-party DMA in which a DMA controller other than the NIC performs transfers, an Ethernet network controller typically has an 8P8C socket where the network cable is connected. Older NICs also supplied BNC, or AUI connections, a few LEDs inform the user of whether the network is active, and whether or not data transmission occurs. Ethernet network controllers typically support 10 Mbit/s Ethernet,100 Mbit/s Ethernet, such controllers are designated as 10/100/1000, meaning that they can support a notional maximum transfer rate of 10,100 or 1000 Mbit/s. 10 Gigabit Ethernet NICs are also available, and, as of November 2014, are beginning to be available on computer motherboards, multiqueue NICs provide multiple transmit and receive queues, allowing packets received by the NIC to be assigned to one of its receive queues. The hardware-based distribution of the interrupts, described above, is referred to as receive-side scaling, purely software implementations also exist, such as the receive packet steering and receive flow steering. Examples of such implementations are the RFS and Intel Flow Director, with multiqueue NICs, additional performance improvements can be achieved by distributing outgoing traffic among different transmit queues. By assigning different transmit queues to different CPUs/cores, various operating systems internal contentions can be avoided and those NICs support, Accessing local and remote memory without involving the remote CPU
3.
Network switch
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A network switch is a computer networking device that connects devices together on a computer network by using packet switching to receive, process, and forward data to the destination device. Unlike less advanced network hubs, a network switch forwards data only to one or multiple devices that need to receive it, a network switch is a multiport network bridge that uses hardware addresses to process and forward data at the data link layer of the OSI model. Switches for Ethernet are the most common form and the first Ethernet switch was introduced by Kalpana in 1990, Switches also exist for other types of networks including Fibre Channel, Asynchronous Transfer Mode, and InfiniBand. A switch is a device in a network that electrically and logically connects together other devices. Multiple data cables are plugged into a switch to enable communication between different networked devices, Switches manage the flow of data across a network by transmitting a received network packet only to the one or more devices for which the packet is intended. Each networked device connected to a switch can be identified by its network address and this maximizes the security and efficiency of the network. Because broadcasts are still being forwarded to all connected devices, the newly formed network segment continues to be a broadcast domain, an Ethernet switch operates at the data link layer of the OSI model to create a separate collision domain for each switch port. In full duplex mode, each switch port can simultaneously transmit and receive, in the case of using a repeater hub, only a single transmission could take place at a time for all ports combined, so they would all share the bandwidth and run in half duplex. Necessary arbitration would result in collisions, requiring retransmissions. The network switch plays an role in most modern Ethernet local area networks. Mid-to-large sized LANs contain a number of linked managed switches, in most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may include a telephone interface for Voice over IP protocol. Segmentation involves the use of a bridge or a switch to split a larger collision domain into smaller ones in order to reduce collision probability, in the extreme case, each device is located on a dedicated switch port. In contrast to an Ethernet hub, there is a separate collision domain on each of the switch ports and this allows computers to have dedicated bandwidth on point-to-point connections to the network and also to run in full-duplex without collisions. Full-duplex mode has one transmitter and one receiver per collision domain. Switches may operate at one or more layers of the OSI model, including the data link, a device that operates simultaneously at more than one of these layers is known as a multilayer switch. In switches intended for use, built-in or modular interfaces make it possible to connect different types of networks, including Ethernet, Fibre Channel, RapidIO, ATM. This connectivity can be at any of the layers mentioned, while the layer-2 functionality is adequate for bandwidth-shifting within one technology, interconnecting technologies such as Ethernet and token ring is performed easier at layer 3 or via routing
4.
Ethernet
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Ethernet /ˈiːθərnɛt/ is a family of computer networking technologies commonly used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as IEEE802.3, over time, Ethernet has largely replaced competing wired LAN technologies such as token ring, FDDI and ARCNET. The original 10BASE5 Ethernet uses coaxial cable as a medium, while the newer Ethernet variants use twisted pair. Over the course of its history, Ethernet data transfer rates have increased from the original 2.94 megabits per second to the latest 100 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. As per the OSI model, Ethernet provides services up to, since its commercial release, Ethernet has retained a good degree of backward compatibility. Features such as the 48-bit MAC address and Ethernet frame format have influenced other networking protocols, the primary alternative for some uses of contemporary LANs is Wi-Fi, a wireless protocol standardized as IEEE802.11. Ethernet was developed at Xerox PARC between 1973 and 1974 and it was inspired by ALOHAnet, which Robert Metcalfe had studied as part of his PhD dissertation. In 1975, Xerox filed a patent application listing Metcalfe, David Boggs, Chuck Thacker, in 1976, after the system was deployed at PARC, Metcalfe and Boggs published a seminal paper. Metcalfe left Xerox in June 1979 to form 3Com and he convinced Digital Equipment Corporation, Intel, and Xerox to work together to promote Ethernet as a standard. The so-called DIX standard, for Digital/Intel/Xerox, specified 10 Mbit/s Ethernet, with 48-bit destination and source addresses and it was published on September 30,1980 as The Ethernet, A Local Area Network. Data Link Layer and Physical Layer Specifications, version 2 was published in November,1982 and defines what has become known as Ethernet II. Formal standardization efforts proceeded at the time and resulted in the publication of IEEE802.3 on June 23,1983. Ethernet initially competed with two largely proprietary systems, Token Ring and Token Bus, in the process, 3Com became a major company. 3Com shipped its first 10 Mbit/s Ethernet 3C100 NIC in March 1981, 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 for a time, with drivers for DOS, by the early 1990s, Ethernet became so prevalent that it was a must-have feature for modern computers, and Ethernet ports began to appear on some PCs and most workstations. This process was sped up with the introduction of 10BASE-T and its relatively small modular connector. Since then, Ethernet technology has evolved to meet new bandwidth, in addition to computers, Ethernet is now used to interconnect appliances and other personal devices
5.
Apple Inc.
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Apple is an American multinational technology company headquartered in Cupertino, California that designs, develops, and sells consumer electronics, computer software, and online services. Apples consumer software includes the macOS and iOS operating systems, the media player, the Safari web browser. Its online services include the iTunes Store, the iOS App Store and Mac App Store, Apple Music, Apple was founded by Steve Jobs, Steve Wozniak, and Ronald Wayne in April 1976 to develop and sell personal computers. It was incorporated as Apple Computer, Inc. in January 1977, Apple joined the Dow Jones Industrial Average in March 2015. In November 2014, Apple became the first U. S. company to be valued at over US$700 billion in addition to being the largest publicly traded corporation in the world by market capitalization. The company employs 115,000 full-time employees as of July 2015 and it operates the online Apple Store and iTunes Store, the latter of which is the worlds largest music retailer. Consumers use more than one billion Apple products worldwide as of March 2016, Apples worldwide annual revenue totaled $233 billion for the fiscal year ending in September 2015. This revenue accounts for approximately 1. 25% of the total United States GDP.1 billion, the corporation receives significant criticism regarding the labor practices of its contractors and its environmental and business practices, including the origins of source materials. Apple was founded on April 1,1976, by Steve Jobs, Steve Wozniak, the Apple I kits were computers single-handedly designed and hand-built by Wozniak and first shown to the public at the Homebrew Computer Club. The Apple I was sold as a motherboard, which was less than what is now considered a personal computer. The Apple I went on sale in July 1976 and was market-priced at $666.66, Apple was incorporated January 3,1977, without Wayne, who sold his share of the company back to Jobs and Wozniak for $800. 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 $118m, the Apple II, also invented by Wozniak, was introduced on April 16,1977, at the first West Coast Computer Faire. It differed from its rivals, the TRS-80 and Commodore PET, because of its character cell-based color graphics. While early Apple II models used 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 platform for the first killer app of the business world, VisiCalc. VisiCalc created a market for the Apple II and gave home users an additional reason to buy an Apple II. Before VisiCalc, Apple had been a distant third place competitor to Commodore, by the end of the 1970s, Apple had a staff of computer designers and a production line
6.
Power Mac G4
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The Power Mac G4 is a series of personal computers that were designed, manufactured, and sold by Apple between 1999 and 2004. They used the PowerPC G4 series of microprocessors and they were heralded by Apple to be the first personal supercomputers, reaching speeds of 4 to 20 Gigaflops. They were the last Macintosh computers able to boot natively to Classic Mac OS. The original Apple Power Mac G4, code name Yikes. was introduced at the Seybold conference in San Francisco on August 31,1999, in October 1999, Apple was forced to postpone the 500 MHz because of poor yield of the 500 MHz chips. The higher-speed models, code name Sawtooth, used a greatly modified motherboard design with AGP 2x graphics, in December 1999, the entire Power Mac G4 line was updated to the AGP motherboard. The machines featured DVD-ROM drives as standard, the 400 MHz and 450 MHz versions had 100 MB Zip drives as standard equipment, and as an option on the 350 MHz Sawtooth. This series had a 100 MHz system bus and four PC100 SDRAM slots for up to 2 GB of RAM, the AGP Power Macs were the first to include an AirPort slot and DVI video port. The computers could house a total of three drives, two 128GB ATA hard drives and up to a single 20GB SCSI hard drive, with the installation of a SCSI card. The 500 MHz version was reintroduced on February 16,2000, DVD-RAM and Zip drives featured on these later 450 MHz and 500 MHz versions and were an option on the 400 MHz. Apples marketing name for all these early AGP models is Power Mac AGP Graphics, the code name Sawtooth was used internally before release and is a popular designation among enthusiasts. The design was updated at the Macworld Expo New York on July 19,2000, the new revision included dual-processor 450 MHz and 500 MHz versions, and it was also the first personal computer to include gigabit Ethernet as standard. The dual 500 MHz models featured DVD-RAM optical drive, Zip drives were optional on all models. These models also introduced Apples proprietary Apple Display Connector video port, Apples marketing name for this series is the Power Mac Gigabit Ethernet. A new line with a revamped motherboard but the familiar Graphite case debuted on January 9,2001 and it was essentially a future Quicksilver inside an older case. Motorola had added a pipeline stage in the new PowerPC G4 design to achieve faster clock frequencies. The models were offered in 466 MHz,533 MHz, dual 533 MHz,667 MHz and 733 MHz configurations, the number of RAM slots was reduced to three, accommodating up to 1.5 GB of PC133 SDRAM. The 733 MHz model was the first Macintosh to include a built-in DVD-R or Apple-branded SuperDrive and this was also the first series of Macs to include an nVidia graphics card, the GeForce 2MX. At Macworld Expo New York on July 18,2001, a new line debuted featuring a redesigned case known as Quicksilver
7.
Intel
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Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California that was founded by Gordon Moore and Robert Noyce. It is the worlds largest and highest valued semiconductor chip makers based on revenue, and is the inventor of the x86 series of microprocessors, Intel supplies processors for computer system manufacturers such as Apple, Lenovo, HP, and Dell. Intel Corporation was founded on July 18,1968, by semiconductor pioneers Robert Noyce and Gordon Moore, the companys name was conceived as portmanteau of the words integrated and electronics. The fact that intel is the term for intelligence information made the name appropriate. Intel was a developer of SRAM and DRAM memory chips. Although Intel created the worlds first commercial microprocessor chip in 1971, during the 1990s, Intel invested heavily in new microprocessor designs fostering the rapid growth of the computer industry. The Open Source Technology Center at Intel hosts PowerTOP and LatencyTOP, and supports other projects such as Wayland, Intel Array Building Blocks, and Threading Building Blocks. Client Computing Group – 55% of 2016 revenues – produces hardware components used in desktop, data Center Group – 29% of 2016 revenues – produces hardware components used in server, network, and storage platforms. Internet of Things Group – 5% of 2016 revenues – offers platforms designed for retail, transportation, industrial, buildings, non-Volatile Memory Solutions Group – 4% of 2016 revenues – manufactures NAND flash memory products primarily used in solid-state drives. Intel Security Group – 4% of 2016 revenues – produces software, particularly security, programmable Solutions Group – 3% of 2016 revenues – manufactures programmable semiconductors. In 2016, Dell accounted for 15% of Intels total revenues, Lenovo accounted for 13% of total revenues, in the 1980s, Intel was among the top ten sellers of semiconductors in the world. In 1991, Intel became the biggest chip maker by revenue and has held the position ever since, other top semiconductor companies include TSMC, Advanced Micro Devices, Samsung, Texas Instruments, Toshiba and STMicroelectronics. Competitors in PC chip sets include Advanced Micro Devices, VIA Technologies, Silicon Integrated Systems, however, the cross-licensing agreement is canceled in the event of an AMD bankruptcy or takeover. Some smaller competitors such as VIA Technologies produce low-power x86 processors for small factor computers, however, the advent of such mobile computing devices, in particular, smartphones, has in recent years led to a decline in PC sales. Since over 95% of the worlds smartphones currently use processors designed by ARM Holdings, ARM is also planning to make inroads into the PC and server market. Intel has been involved in disputes regarding violation of antitrust laws. Intel was founded in Mountain View, California in 1968 by Gordon E. Moore, a chemist, and Robert Noyce, arthur Rock helped them find investors, while Max Palevsky was on the board from an early stage. Moore and Noyce had left Fairchild Semiconductor to found Intel, Rock was not an employee, but he was an investor and was chairman of the board
8.
Small form-factor pluggable transceiver
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The small form-factor pluggable is a compact, hot-pluggable transceiver used for both telecommunication and data communications applications. The form factor and electrical interface are specified by an agreement under the auspices of the SFF Committee. It is an industry format jointly developed and supported by many network component vendors. The SFP interfaces a network device motherboard to a fiber optic or copper networking cable, SFP transceivers are designed to support SONET, gigabit Ethernet, Fibre Channel, and other communications standards. Due to its size, SFP obsolesces the formerly ubiquitous gigabit interface converter. In fact, no device with this name has ever been defined in the MSAs, transceivers are most often designated by the standard transmission speed on the medium, but sometimes they are labeled with their nominal Ethernet speed or a higher speed the manufacturer specifies. Not compatible with SX or 100BASE-FX, based on LX but engineered to work with a multi-mode fiber using a standard multi-mode patch cable rather than a mode-conditioning cable commonly used to adapt LX to multi-mode. Coupled with CWDM, these double the density of fiber links. They are not compatible with Fiber channel or SONET, unlike non-SFP, copper 1000BASE-T ports integrated into most routers and switches, 1000BASE-T SFPs usually cannot operate at 100BASE-TX speeds. 100 Mbit/s copper and optical - some vendors have shipped 100 Mbit/s limited SFPs for fiber to the home applications and these are relatively uncommon and can be easily confused with 1 Gbit/s SFPs. The enhanced small form-factor pluggable is a version of the SFP that supports data rates up to 16 Gbit/s. The SFP+ specification was first published on May 9,2006, SFP+ supports 8 Gbit/s Fibre Channel,10 Gigabit Ethernet and Optical Transport Network standard OTU2. It is an industry format supported by many network component vendors. 10 Gbit/s SFP+ modules are exactly the same dimensions as regular SFPs, allowing the equipment manufacturer to re-use existing physical designs for 24 and 48-port switches, although the SFP+ standard does not include mention of 16G Fibre Channel it can be used at this speed. Besides the data rate, the big difference between 8G Fibre Channel and 16G Fibre Channel is the encoding method, 64b/66b encoding used for 16G is a more efficient encoding mechanism than 8b/10b used for 8G, and allows for the data rate to double without doubling the line rate. The result is the 14.025 Gbit/s line rate for 16G Fibre Channel, in comparison to earlier XENPAK or XFP modules, SFP+ modules leave more circuitry to be implemented on the host board instead of inside the module. Through the use of an active adapter, SFP+ modules may be used in older equipment with XENPAK ports. SFP+ modules can be described as limiting or linear types, this describes the functionality of the inbuilt electronics, limiting SFP+ modules include a signal amplifier to re-shape the received signal whereas linear ones do not
9.
Optical fiber connector
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An optical fiber connector terminates the end of an optical fiber, and enables quicker connection and disconnection than splicing. The connectors mechanically couple and align the cores of fibers so light can pass, better connectors lose very little light due to reflection or misalignment of the fibers. In all, about 100 fiber optic connectors have been introduced to the market, optical fiber connectors are used to join optical fibers where a connect/disconnect capability is required. Due to the polishing and tuning procedures that may be incorporated into optical connector manufacturing, however, the assembly and polishing operations involved can be performed in the field, for example, to make cross-connect jumpers to size. Most optical fiber connectors are spring-loaded, so the fiber faces are pressed together when the connectors are mated, the resulting glass-to-glass or plastic-to-plastic contact eliminates signal losses that would be caused by an air gap between the joined fibers. Every fiber connection has two values, Attenuation or insertion loss Reflection or return loss, measurements of these parameters are now defined in IEC standard 61753-1. The standard gives five grades for insertion loss from A to D, the other parameter is return loss, with grades from 1 to 5. A variety of optical fiber connectors are available, but SC, typical connectors are rated for 500–1,000 mating cycles. The main differences among types of connectors are dimensions and methods of mechanical coupling, generally, organizations will standardize on one kind of connector, depending on what equipment they commonly use. Different connectors are required for multimode, and for single-mode fibers, in many data center applications, small and multi-fiber connectors are replacing larger, older styles, allowing more fiber ports per unit of rack space. In such settings, protective enclosures are used, and fall into two broad categories, hermetic and free-breathing. Hermetic cases prevent entry of moisture and air but, lacking ventilation, free-breathing enclosures, on the other hand, allow ventilation, but can also admit moisture, insects and airborne contaminants. Selection of the correct housing depends on the cable and connector type, the location, careful assembly is required to ensure good protection against the elements. To ensure the integrity of optical fiber connections and housing seals, many types of optical connector have been developed at different times, and for different purposes. Many of them are summarized in the tables below, modern connectors typically use a physical contact polish on the fiber and ferrule end. This is a convex surface with the apex of the curve accurately centered on the fiber. Higher grades of polish give less insertion loss and lower back reflection, many connectors are available with the fiber end face polished at an angle to prevent light that reflects from the interface from traveling back up the fiber. Because of the angle, the light does not stay in the fiber core
10.
Modular connector
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A modular connector is an electrical connector that was originally designed for use in telephone wiring, but has since been used for many other purposes. Many applications that used a bulkier, more expensive connector have converted to modular connectors. Probably the most well known applications of modular connectors are for telephone jacks and for Ethernet jacks, Modular connectors were originally used in the Registration Interface system, mandated by the Federal Communications Commission in 1976 in which they became known as registered jacks. The registered jack specifications define the wiring patterns of the jacks, instead, these latter aspects are covered by ISO standard 8877, first used in ISDN systems. TIA/EIA-568 is a standard for data circuits wired on modular connectors, other systems exist for assigning signals to modular connectors, physical interchangeability of plugs and jacks does not ensure interoperation, nor protection from electrical damage to circuits. For example, modular cables and connectors have used to supply low-voltage AC or DC power. Modular connectors also go by the names modular phone jack/plug, RJ connector, the term modular connector arose from its original use in a novel system of cabling designed to make telephone equipment more modular. This includes the 4P4C handset connector, a very popular use of 8P8C today is Ethernet over twisted pair, and that may be the most well known context in which the name RJ45 is known, even though it has nothing to do with the RJ45 standard. Likewise, the 4P4C connector is sometimes called RJ9 or RJ22, Modular connectors were originally developed and patented by General Cable Corp in 1974. They replaced the hard-wired connections on most Western Electric telephones around 1976, at the same time, they began to replace screw terminals and larger 3 and 4 pin telephone jacks in buildings. Modular connectors have gender, plugs are considered to be male, while jacks or sockets are considered to be female, plugs are used to terminate loose cables and cords, while jacks are used for fixed locations on surfaces such as walls and panels, and on equipment. Other than telephone extension cables, cables with a plug on one end. Instead, cables are connected using an adapter, which consists of two female jacks wired back-to-back. Modular connectors are designed to latch together, a spring-loaded tab on the plug snaps into a jack so that the plug cannot be pulled out. To remove the plug, the latching tab must be depressed, the standard and most common way to install a jack in a wall or panel is with the tab side down. This usually makes it easier to operate the tab when removing the plug, because the person grabs the plug with thumb on top, the modular connector suffers from a design flaw or weakness however, as the fragile latching tab easily snags on other cables and breaks off. When this happens, the connector is still functional, but the crucial latching feature is lost, some higher quality cables have a flexible sleeve called a boot over the plug, or a special tab design, to prevent this. These cables are marketed as snagless
11.
D-subminiature
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The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield, when they were introduced, D-subs were among the smallest connectors used on computer systems. The part containing pin contacts is called the male connector or plug, the sockets shield fits tightly inside the plugs shield. Panel mounted connectors usually have threaded nuts that accept screws on the cable end connector cover that are used for locking the connectors together, occasionally the nuts may be found on a cable end connector if it is expected to connect to another cable end. When screened cables are used, the shields are connected to the screens of the cables. This creates a continuous screen covering the whole cable and connector system. The D-sub series of connectors was introduced by Cannon in 1952, each shell size usually corresponds to a certain number of pins or sockets, A with 15, B with 25, C with 37, D with 50, and E with 9. For example, DB-25 denotes a D-sub with a 25-position shell size and this spacing is called normal density. The suffixes M and F are sometimes used instead of the original P and S for plug, later D-sub connectors added extra pins to the original shell sizes, and their names follow the same pattern. For example, the DE-15, usually found in VGA cables, has 15 pins in three rows, all surrounded by an E size shell, the pins are spaced at 0.090 inches horizontally and 0.078 inches vertically, in what is called high density. The other connectors with the pin spacing are the DA-26, DB-44, DC-62, DD-78. They all have three rows of pins, except the DD-78 which has four, and the DF-104 which has five rows in a new, the double density series of D-sub connectors features even denser arrangements and consists of the DE-19, DA-31, DB-52, DC-79, and DD-100. These each have three rows of pins, except the DD-100, which has four, however, this naming pattern is not always followed. It is now common to see DE-9 connectors sold as DB-9 connectors, DB-9 nearly always refers to a 9-pin connector with an E size shell. Cannon also produced combo D-subs with larger contacts in place of some of the contacts, for use for high-current, high-voltage. The DB-13W3 variant was used for high-performance video connections, this variant provided 10 regular pins plus three coaxial contacts for the red, green, and blue video signals. Some variants have current ratings up to 40 A or operating voltages as high as 13,500 V, others are waterproof, a smaller type of connector derived from the D-sub is called the microminiature D, or micro-D, which is a trademark of ITT Cannon. It is about half the length of a D-sub, a further family of connectors of similar appearance to the D-sub family uses names such as HD-50 and HD-68, and has a D-shaped shell about half the width of a DB25
12.
Data center
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A data center is a facility used to house computer systems and associated components, such as telecommunications and storage systems. It generally includes redundant or backup power supplies, redundant data communications connections, environmental controls, large data centers are industrial scale operations using as much electricity as a small town. Data centers have their roots in the computer rooms of the early ages of the computing industry. Early computer systems, complex to operate and maintain, required an environment in which to operate. Many cables were necessary to all the components, and methods to accommodate and organize these were devised such as standard racks to mount equipment, raised floors. A single mainframe required a deal of power, and had to be cooled to avoid overheating. Security became important – computers were expensive, and were used for military purposes. Basic design-guidelines for controlling access to the room were therefore devised. During the boom of the industry, and especially during the 1980s, users started to deploy computers everywhere. However, as information technology operations started to grow in complexity, the advent of Unix from the early 1970s led to the subsequent proliferation of freely available Linux-compatible PC operating-systems during the 1990s. These were called servers, as timesharing operating systems like Unix rely heavily on the model to facilitate sharing unique resources between multiple users. The use of the data center, as applied to specially designed computer rooms. The boom of data centers came during the bubble of 1997–2000. Companies needed fast Internet connectivity and non-stop operation to deploy systems, installing such equipment was not viable for many smaller companies. Many companies started building very large facilities, called Internet data centers, New technologies and practices were designed to handle the scale and the operational requirements of such large-scale operations. These practices eventually migrated toward the data centers, and were adopted largely because of their practical results. Data centers for cloud computing are called cloud data centers, but nowadays, the division of these terms has almost disappeared and they are being integrated into a term data center. Standards documents from accredited professional groups, such as the Telecommunications Industry Association, well-known operational metrics for data-center availability can serve to evaluate the commercial impact of a disruption
