Networking.docx

Understanding Cables and Connectors The devices used with a computer need to attach to the motherboard somehow. They do so through the use of ports and cables. A port is a generic name for any connector on a computer or peripheral into which a cable can be plugged. A cable is simply a way of connect...

Understanding Cables and Connectors The devices used with a computer need to attach to the motherboard somehow. They do so through the use of ports and cables. A port is a generic name for any connector on a computer or peripheral into which a cable can be plugged. A cable is simply a way of connecting a peripheral or other device to a computer using multiple copper or fiber-optic conductors inside a common wrapping or sheath. Typically, cables connect two ports: one on the computer and one on some other device. The A+ exam objectives break cables and connectors into two different groups, but really they need to be discussed together. After all, a cable without a connector doesn’t do much good, and neither does a connector without a cable. In the following sections, we’ll look at four different classifications of cables and the connectors that go with them: video, hard drive, multipurpose, and peripheral.  For the A+ exam, you will also need to be familiar with network cables and connectors. We will cover those in depth in Chapter 6, “Networking Fundamentals.” Video Cables and Connectors Computer displays are ubiquitous—they’re easily the most widely used peripheral. Different standards exist to connect displays to the computer, and you need to be familiar with five of them for the exam: VGA, DVI (and variants), HDMI, mini-HDMI, and DisplayPort. We will start with the older technologies and work toward the present. 134 Video Graphics Array Connector The Video Graphics Array (VGA) connector was the de facto video standard for computers for years and is still in use today. First introduced in 1987 by IBM, it was quickly adopted by other PC manufacturers. The term VGA is often used interchangeably to refer to generic analog video, the 15-pin video connector, or a 640 × 480 screen resolution (even though the VGA standard can support much higher resolutions). Figure 3.1 shows a VGA port, as well as the male connector that plugs into the port. Nearly all VGA connectors are blue. Figure 3.1 VGA connector and port Understanding D-Sub Ports and Connectors The VGA connector is an example of a D-subminiature connector, also known as a D-sub connector. For a number of years, D-sub was the most common style of connector found on computers. Their names are typically designated with DX-n, where the letter X is replaced by a letter from A to E, which refers to the size of the connector, and the letter n is replaced by the number of pins or sockets in the connector. D-sub connectors are usually shaped like a trapezoid and have at least two rows of pins with no other keying structure or landmark, as you can see in Figure 3.2. At the bottom center in Figure 3.2 is a DE-15F 15-pin display-connector port, which may also be referred to as an HD-15 or DB-15 port. The top one is a classic DB-25 parallel port, and the bottom left is a DB-9 serial port. The IEEE 1394 (FireWire) and two dusty USB ports are shown for a size comparison. The “D” shape ensures that only one orientation is possible. If you try to connect them upside down or try to connect a male connector to another male connector, they just won’t go together and the connection can’t be made. By the way, male interfaces have pins, while female interfaces have sockets. Be on the lookout for the casual use of DB to represent any D-sub connector. This is very common and is accepted as an unwritten de facto standard, even if some are technically DE- or DA- connectors. Also note that you will see them written without the hyphen or with a space, such as DB15 or DB 15. 135 Figure 3.2 D-sub ports VGA technology is the only one on the objectives list that is analog. It has been superseded by newer digital standards, such as DVI and HDMI, and it was supposed to be phased out starting in 2013. A technology this widely used will be around for quite a while, though, and you’ll still see a lot of these in the wild (or still in use).  All the video connector types introduced from here on are digital standards. Digital Visual Interface In an effort to leave analog VGA standards and return to digital video, which can typically be transmitted farther and at higher quality than analog, a series of connectors known collectively as Digital Visual Interface (DVI) was developed for the technology of the same name. DVI was released in 1999. At first glance, the DVI connector might look like a standard D-sub connector. On closer inspection, however, it begins to look somewhat different. For one thing, it has quite a few pins, and for another, the pins it has are asymmetrical in their placement on the connector. The DVI connector is usually white and about an inch long. Figure 3.3 shows what the connector looks like coming from the monitor. 136 Figure 3.3 DVI connector There are three main categories of DVI connectors: DVI-A DVI-A is an analog-only connector. The source must produce analog output, and the monitor must understand analog input. DVI-D DVI-D is a digital-only connector. The source must produce digital output, and the monitor must understand digital input. DVI-I DVI-I is a combination analog/digital connector. The source and monitor must both support the same technology, but this cable works with either a digital or an analog signal. The DVI-D and DVI-I connectors come in two varieties: single-link and dual-link. The dual-link options have more conductors—taking into account the six center conductors—than their single-link counterparts; therefore, the dual-link connectors accommodate higher speed and signal quality. The additional link can be used to increase screen resolution for devices that support it. Figure 3.4 illustrates the five types of connectors that the DVI standard specifies. Figure 3.4 Types of DVI connectors 137 DVI-A and DVI-I analog quality is superior to that of VGA, but it’s still analog, meaning that it is more susceptible to noise. However, the DVI analog signal will travel farther than the VGA signal before degrading beyond usability. Nevertheless, the DVI-A and VGA interfaces are pin-compatible, meaning that a simple passive DVI to VGA adapter, as shown in Figure 3.5, is all that is necessary to convert between the two. As you can see, the analog portion of the connector, if it exists, comprises the four separate color and sync pins and the horizontal blade that they surround, which happens to be the analog ground lead that acts as a ground and physical support mechanism even for DVI-D connectors. Figure 3.5 DVI to VGA adapter It’s important to note that DVI-I cables and interfaces are designed to interconnect two analog or two digital devices; they cannot convert between analog and digital. DVI cables must support a signal of at least 4.5 meters, but better cable assemblies, stronger transmitters, and active boosters result in signals extending over longer distances. One thing to note about analog vs. digital display technologies is that all graphics adapters and all monitors deal with digital information. It is only the connectors and cabling that can be made to support analog transmission. Before DVI and HDMI encoding technologies were developed, consumer digital video display connectors could not afford the space to accommodate the number of pins that would have been required to transmit 16 or more bits of color information per pixel. For this reason, the relatively few conductors of the inferior analog signaling in VGA were appealing. High-Definition Multimedia Interface High-Definition Multimedia Interface (HDMI) is an all-digital technology that advances the work of DVI to include the same dual-link resolutions using a standard HDMI cable but with higher motion-picture frame rates and digital audio right on the same connector. HDMI was introduced in 2002, which makes it seem kind of old in technology years, but it’s a great, fast, reliable connector that will probably be around for several years to come. HDMI cabling also supports an optional Consumer Electronics Control (CEC) feature that allows transmission of signals from a remote-control unit to control multiple devices without separate cabling to carry infrared signals. HDMI cables, known as Standard and High Speed, exist today in the consumer space. Standard cables are rated for 720p resolution as well as 1080i, but not 1080p. High Speed138cables are capable of supporting not only 1080p, but also the newer 4K and 3D technologies. Figure 3.6 shows an HDMI cable and port. Figure 3.6 HDMI cable and port In June 2006, revision 1.3 of the HDMI specification was released to support the bit rates necessary for HD DVD and Blu-ray disc. This version also introduced support for “deep color,” or color depths of at least one billion colors, including 30-, 36-, and 48-bit color. However, not until version 1.4, which was released in May 2009, was the High Speed HDMI cable initially required. With version 1.4 came HDMI capability for the controlling system—the television, for instance—to relay Ethernet frames between its connected components and the Internet, alleviating the need for each and every component to find its own access to the LAN for Internet access. Both Standard and High Speed cables are available with this Ethernet channel. Each device connected by such a cable must also support the HDMI Ethernet Channel specification, however. Additional advances that were first seen in version 1.4 were 3D support, 4K resolution (but only at a 30 Hz refresh rate), an increased 120 Hz refresh rate for the 1080 resolutions, and an Audio Return Channel (ARC) for televisions with built-in tuners to send audio back to an A/V receiver without using a separate output cable. Version 1.4 also introduced the anti-vibration139Type-E locking connector for the automotive-video industry and cables that can also withstand vibration as well as the hot/cold extremes that are common in the automotive world. Version 2.0 of HDMI (2013) introduced no new cable requirements. In other words, the existing High Speed HDMI cable is fully capable of supporting all new version 2 enhancements. These enhancements include increasing the 4K refresh rate to 60 Hz, a 21:9 theatrical widescreen aspect ratio, and 32-channel audio. Note that 7.1 surround sound comprises only eight channels, supporting the more lifelike Rec. 2020 color space and multiple video and audio streams to the same output device for multiple users. Version 2.0a, released in 2015, primarily added high dynamic range (HDR) video, but it does not require any new cables or connectors. The most recent version (as of this writing) is HDMI 2.1, released in November 2017. Version 2.1 specifies a new cable type called 48G, which provides for 48 Gbps bandwidth. 48G cables are backward compatible with older HDMI versions. You can also use older cables with 48G-capable devices, but you just won’t get the full 48 Gbps bandwidth. HDMI 2.1 also provides for 120 Hz refresh rates for 4K, 8K, and 10K video, and supports enhanced Audio Return Channel (eARC), which is needed for object-based audio formats, such as DTS:X and Dolby Atmos. Even though the HDMI connector is not the same as the one used for DVI, the two technologies are electrically compatible. HDMI is compatible with DVI-D and DVI-I interfaces through proper adapters, but HDMI’s audio and remote-control pass-through features are lost. Additionally, 3D video sources work only with HDMI. Figure 3.7 shows a DVI to HDMI adapter between DVI-D and the Type-A 19-pin HDMI interface. Compare the DVI-D interface to the DVI-I interface of Figure 3.5, and note that the ground blade on the DVI-D connector is narrower than that of the DVI-A and DVI-I connectors. The DVI-D receptacle does not accept the other two plugs for this reason, as well as because the four analog pins around the blade have no sockets in the DVI-D receptacle. Figure 3.7 DVI to HDMI adapter Unlike DVI-D and, by extension DVI-I, DVI-A and VGA devices cannot be driven passively by HDMI ports directly. An HDMI to VGA adapter must be active in nature, powered either externally or through the HDMI interface itself. HDMI cables should meet the signal requirements of the latest specification. As a result, and as with DVI, the maximum cable length is somewhat variable. For HDMI, cable length depends heavily on the materials used to construct the cable. Passive cables tend to extend140no farther than 15 meters, while adding electronics within the cable to create an active version results in lengths as long as 30 meters. Mini-HDMI There are multiple versions of HDMI connectors in the marketplace. The standard connector that you’re probably used to seeing, and the one shown in Figure 3.6 and Figure 3.7, is the 19-pin Type-A connector. The Type-A connector and the 29-pin Type-B connector were specified in HDMI version 1.0 and haven’t changed much since then. Type-B connectors were intended for higher-resolution products but are not used in the market today. HDMI version 1.3 specified a smaller 19-pin Type-C connector for portable devices. The Type-C connector, also referred to as a mini-HDMI connector, is compatible with the Type-A connector, but it still requires an adapter due to its smaller size. HDMI version 1.4 specified two more interfaces: Type-D and Type-E. If Type-C is a mini-HDMI interface, then you might refer to the Type-D connector as micro-HDMI. Figure 3.8 shows all five HDMI connectors. Also compatible with Type-A interfaces because they have the same 19 pins, Type-D interfaces require just a simple adapter for conversion. Figure 3.8 HDMI connector types  By C0nanPayne - Based on File: HDMI Connector.jpg, CC0, https://commons.wikimedia.org/w/index .php?curid=58368257 The mini-HDMI and micro-HDMI connectors are most often used on smaller portable devices, such as tablets, smartphones, and digital cameras. As mentioned previously, the Type-E connector has a locking mechanism and is intended for use in automobiles or other environments that are susceptible to vibration, which could cause a connector and cable to become disconnected. DisplayPort DisplayPort is a royalty-free digital display interface from the Video Electronics Standards Association (VESA) that uses less power than other digital interfaces and VGA. Introduced in 2008, it’s designed to replace VGA and DVI. To help ease the transition, it’s backward141compatible with both standards, using an adapter. In addition, an adapter allows HDMI and DVI voltages to be lowered to those required by DisplayPort because it is functionally similar to HDMI and DVI. DisplayPort cables can extend 3 meters, unless an active cable powers the run, in which case the cable can extend to 33 meters. DisplayPort is intended primarily for video, but, like HDMI, it can transmit audio and video simultaneously. Figure 3.9 shows a DisplayPort port on a laptop as well as a connector. The DisplayPort connector latches itself to the receptacle with two tiny hooks. A push-button mechanism serves to release the hooks for removal of the connector from the receptacle. Note the beveled keying at the bottom-left corner of the port. Figure 3.9 A DisplayPort port and cable The DisplayPort standard also specifies a smaller connector, known as the Mini DisplayPort (MDP) connector. The MDP is electrically equivalent to the full-size DP connector and features a beveled keying structure, but it lacks the latching mechanism present in the DP connector. The MDP connector looks identical to a Thunderbolt connector, which we will cover in the “Multipurpose Cables and Connectors” section later in this chapter. Hard Drive Cables and Connectors At the beginning of this chapter, we said that we were going to move outside the box and talk about external peripherals, cables, and connectors. For the most part that’s true, but here we need to take a small digression to talk about connecting hard drives, most of which are internal. Some of this you already learned in Chapter 2, “Internal Expansion, Storage Devices, and Power Supplies,” so this could feel like a review. Of course, there are SATA and PATA connectors, but we’ll also throw in two new ones—SCSI and eSATA.  Optical drives use the same connectors as hard drives. Remember that all drives need some form of connection to the motherboard so that the computer can “talk” to the disk drive. Regardless of whether the connection is built into the motherboard (onboard) or on an adapter card (off-board), internal or external, the standard for the attachment is based on the drive’s requirements. These connections are known as drive interfaces. The interfaces consist of circuitry and a port, or header. 142 Serial Advanced Technology Attachment The most common hard drive connector used today is Serial Advanced Technology Attachment (SATA). Figure 3.10 shows SATA headers, which you have seen before, and a SATA cable. Note that the SATA cable is flat, and the connector is keyed to fit into the motherboard header in only one way. SATA data cables have a 7-pin connector. SATA power cables have 15 pins and are wider than the data connector. Figure 3.10 SATA connectors and cable The SATA we’ve discussed so far is internal, but there’s an external version as well, appropriately named external SATA (eSATA). It uses the same technology, only in an external connection. The port at the bottom center of Figure 3.11 is eSATA. It entered the market in 2003, is mostly intended for hard drive use, and can support up to 15 devices on a single bus. Figure 3.11 eSATA 143 Table 3.1 shows some of the eSATA specifications. Table 3.1 eSATA specifications Version Year Speed Names Revision 1.0 2003 1.5 Gbps SATA I, SATA 1.5Gb/s Revision 2.0 2005 3.0 Gbps SATA II, SATA 3Gb/s Revision 3.0 2009 6.0 Gbps SATA III, SATA 6Gb/s You will commonly see the third generation of eSATA (and SATA) referred to as SATA 6 or SATA 6Gb/s. This is because if they called it SATA 3, there would be confusion with the second generation, which had transfer speeds of 3.0 Gbps. An interesting fact about eSATA is that the interface does not provide power, which is a big negative compared to its contemporary high-speed serial counterparts. To overcome this limitation, there is another eSATA port that you might see, called Power over eSATA, eSATA+, eSATAp, or eSATA/USB. It’s essentially a combination eSATA and USB port. Since the port is a combination of two others, neither sanctioning body officially recognizes it (which is probably why there are so many names—other companies call it what they want to). Figure 3.12 shows this port. Figure 3.12 USB over eSATA You can see that this port is slightly different from the one in Figure 3.11, and it’s also marked with a USB icon next to the eSATA one. On the market, you can purchase cables that go from this port to an eSATA device and provide it with power via the eSATAp port. Parallel Advanced Technology Attachment Prior to SATA, the most popular hard drive connector was Integrated Drive Electronics (IDE), which has now been renamed to Parallel Advanced Technology Attachment (PATA). There is no difference between PATA and IDE, other than the name. Figure 3.13 shows PATA connectors on a motherboard next to a PATA cable. Refer back to Chapter 2, Figure 2.9 to see a direct comparison of SATA and PATA connectors on a hard drive. Figure 3.13 PATA connectors and cable PATA drives use a 40-pin flat data cable, and there are a few things to note about it. First, there is an off-colored stripe (often red, pink, or blue) along one edge of the cable to designate where pin 1 is. On a PATA drive, pin 1 is always on the edge nearest the power connector. The second thing to note is that there are three connectors—one for the motherboard and two for drives. PATA technology specifies that there can be two drives per cable, in a primary and secondary (or master and slave) configuration. The primary drive will be attached to the other end of the cable, and the secondary, if connected, will use the middle connector. In addition, the drive itself may need to be configured for master or slave by using the jumper block on the drive. Most PATA drives will auto-configure their status based on their position on the cable, but if there is a conflict, they can be manually configured. Power is supplied by a 4-pin power connector known as a Molex connector. Small Computer System Interface A third type of hard drive connector is called Small Computer System Interface (SCSI). The acronym is pronounced “scuzzy,” even though the original designer intended for it to be called “sexy.” The most common usage is for storage devices, but the SCSI standard can be used for other peripherals as well. You won’t see many SCSI interfaces in home145computers—it’s more often found in servers, dedicated storage solutions, and high-end workstations. Early versions of SCSI used a parallel bus interface called SCSI Parallel Interface (SPI). Starting in 2005, SPI was replaced by Serial Attached SCSI (SAS), which, as you may guess, is a serial bus. If you compare SCSI to other popular drive interfaces at the time, SCSI was generally faster but more expensive than its counterparts, such as IDE. SCSI Parallel Interface Although it’s essentially obsolete now, you might find some details of SPI interesting. The first standard, ratified in 1986, was an 8-bit bus that provided for data transfers of 5 Mbps. Because it was an 8-bit bus, it could support up to seven devices. (The motherboard or expansion card header was the eighth.) Each device needed a unique ID from 0 to 7, and devices were attached in a daisy chain fashion. A terminator (essentially a big resistor) needed to be attached to the end of the chain; otherwise, the devices wouldn’t function. In 1994, the 8-bit version was replaced by a 16-bit version that supported up to 15 devices and had a transfer speed of 320 Mbps. Compared to the 100 Mbps supported by IDE at the time, you can see why people wanted SCSI! SPI had different connectors, depending on the standard. 50-pin, 68-pin, and 80-pin connectors were commonly used. Figure 3.14 shows two 50-pin Centronics connectors, which were common for many years. Figure 3.15 shows a terminator, with the top cover removed so that you can see the electronics. Figure 3.14 Two 50-pin SCSI connectors  Serial Attached SCSI Of the newer SCSI implementations, the one you will most likely encounter is SAS. For example, as we mentioned in Chapter 2, most 15,000 rpm hard drives are SAS drives. From an architectural standpoint, SAS differs greatly from SPI, starting with the fact that it’s serial, not parallel. What they do share is the use of the SCSI command architecture, which is a group of commands that can be sent from the controller to the device to make it do something, such as write or retrieve data. A SAS system of hard drives works much like the SATA and PATA systems you’ve already learned about. There’s the controller, the drive, and the cable that connects it. SAS uses its own terminology, though, and adds a component called an expander. Here are the four components of a SAS system: Initiator Think of this as the controller. It sends commands to target devices and receives data back from them. These can be integrated or an add-on card. Each initiator can have a direct connection to 128 devices. Target This is the device, typically a hard drive. It can also be multiple hard drives functioning in a RAID array. Service Delivery Subsystem The service delivery subsystem transmits information between an initiator and a target. Often this is a cable, but it can also be a server backplane (where multiple devices connect). Expander An expander is a device that allows for multiple initiators to be combined into one service delivery subsystem. Through the use of expanders, one initiator can support up to 16,256 devices. 147 Figure 3.16 shows a SAS cable and connector. It’s slightly wider than a SATA power and data connector together. The other end of a cable such as this might have an identical SAS connector or a mini-SAS connector, or it might pigtail into four SATA or mini-SAS connectors. Table 3.2 SAS standards and speeds Standard Year Throughput SAS-1 2005 3 Gbps SAS-2 2009 6 Gbps SAS-3 2013 12 Gbps SAS-4 2017 22.5 Gbps SAS offers the following advantages over SPI: No terminator is required. Up to 16,256 devices can be connected to a single system. Each SAS device has its own link to the controller, so there are no issues with contention (when multiple devices try to use the same link at the same time, causing interference). SAS provides faster data transfer speeds than SPI. SAS devices are compatible with SATA 2.0 and higher—SATA drives can be connected to SAS controllers. With the invention of super-fast M.2 and NVMe hard drives, which you learned about in Chapter 2, it’s hard to say what the future of SAS is. Most likely, SAS will continue to have a place in corporate environments with large-scale storage solutions, while the others will provide leading-edge speed for the workstation environment, particularly among laptops and smaller devices.