Chapter 1: Describing Ports, Cables, and Connectors

Exam Objectives

Understanding fundamental principles of using a personal computer

Identifying ports and cables

In this chapter, you examine the ports on the back of the computer as well as the cables and connectors used to attach devices. In other chapters of this book, you examine different devices, but this chapter looks at getting them all connected. The other devices and chapters include

Printers: Book III, Chapter 5

Internal drives: Book II, Chapter 5

Monitors: Book III, Chapter 3

USB devices: Book II, Chapter 1

FireWire devices: Book II, Chapter 1

Modems: Book III, Chapter 2

A CompTIA A+ Certified Professional must be able to identify various types of cables and connectors. This chapter introduces you to the most common cables and connectors that you will encounter when using computer systems.

Identifying Common Computer Ports

Start by looking at the different types of ports on the back of your computer. Ports are connection points on your computer that allow for devices to be connected to your computer. The connection point has a connector that accepts a cable with a matching connector. Knowing what the ports are used for is important when connecting devices to your computer. You might already be familiar with some of the common ports, such as serial, parallel, and USB. In this section, I discuss these ports as well as IEEE 1394 ports, which are often called FireWire.

Serial and parallel ports

Older computers have one parallel port and two serial ports. These ports are used to connect devices, such as modems and printers, to your computer.

There has been a trend in the industry to create legacy-free computers: that is, computers without COM ports, LPT ports, or ISA expansion slots, as well as number of other functional changes. Many new laptops on the market already fit into this category.

Parallel ports send data over multiple wires simultaneously; serial ports send data over only one wire at a time. Parallel communication allows for multiple streams of data, which in the early days, when serial controllers were slow, allowed it to provide higher data transfer rates than serial communication. This is no longer true today.

Parallel ports were implemented on the personal computer when it was introduced by IBM in 1981. IBM used nine-wire cables to connect two devices. This enables the cables, at any given time, to deliver 8 bits of data, with the extra wire being used as a ground. However, because there is no way to accurately control the flow of the signal along each wire in the cable, it is recommended that the length of the cable be less than 6 feet (about 2 meters).

Controlling the flow of data became more of a factor when bidirectional communication (sending and receiving data with the device) was implemented over the parallel port. The standard for bidirectional communication was delivered in 1994 in the IEEE 1284 specification, which allows for high-speed, two-way communication over the parallel port. This also opened two new specifications for the port: the Enhanced Parallel Port (EPP) and the Extended Capabilities Port (ECP). The maximum cable length for an IEEE 1284 cable is about 30 feet (10 meters).

An EPP-type parallel port is used primarily for nonprinter peripherals, and an ECP-type parallel port is designed to accommodate high-speed printers and scanners. To better handle high-speed data communication, the ECP-type parallel port also implements a dynamic memory access (DMA) channel; this grants the port direct access to a section of RAM.

Serial ports, on the other hand, deliver data sequentially down a single wire. Eight bits of digital data are converted into an analog signal by using a system called baud. Baud rate refers to the number of state changes (tones) made on the wire in any given second. If you have heard a fax machine or modem making a connection, you have heard the state changes as a series of squeals. Baud rate is very different from bits per second (bps), which measures the amount of data that is transferred. At one point, 300 bps modems communicated at 300 baud, but compression standards adopted by the communications industry allowed more data to be delivered at the same baud rate. Today, 56 Kbps (57,344 bps) modems communicate at 9,600 baud.

Depending on the baud rate used to transfer data, the length of the cable can range up to 3,000 feet (just over 900 meters). For data transfer rates at 9,600 baud, the maximum cabling length is 250 feet (just over 75 meters). The RS-232C standard (usually simply referred to as RS-232), which is used as a basis of serial communication, recommends a maximum cable length of 50 feet (about 15 meters).

Find out how to troubleshoot serial and parallel port problems by reading Book IV, Chapter 2.

Universal Serial Bus (USB)

USB is a more modern method of communicating using serial communication methodologies. The standards for USB 1.0 were released in 1996, USB 1.1 in 1998, USB 2.0 in 2000, and USB 3.0 in 2008. The goal of USB was to revolutionize how serial communication was conducted. To fulfill this goal, USB uses a cabling system that allows up to 127 devices to be connected. It also delivers power to the devices connected on this bus.

To go along with this new cabling, the specification for USB dictates that all devices should support Plug and Play. With these two pieces of the puzzle put together, USB enables you to plug in devices and have them work without having to worry about power cables or drivers. Some USB devices that require a large amount of power may use a supplemental power supply, but the USB bus will power most devices.

USB 2.0 increased the fastest transfer rate for USB 1.0 from 12 Mbps to 480 Mbps. This has allowed it to be used for devices that require faster transfer rates, such as hard drives and CD-ROMs. USB 3.0 takes that a step further, allowing for device communication up to 5.0 Gbps (also called Super Speed); these devices are becoming popular on the market. For more information about USB, see Book III, Chapter 3.

USB has had a performance boost up to 480 Mbps with the introduction of version 2 of the USB standard. For the exam, you need to pay attention to the version of USB covered in the question. If it is USB 1.0, you are still limited to the 12 Mbps transfer rate, while USB 2.0 is 480 Mbps and USB 3.0 is 5.0 Gbps.

FireWire (IEEE 1394)

FireWire is an Apple trademark for the IEEE 1394 standard. The 1394 standard implements a version of serial communication across a wiring network that is similar to USB. IEEE 1394 enables connecting 63 external devices on a bus that supports between 50 and 400 Mbps. With the release of FireWire 800, transfer rates have approached 800 Mbps. One of the goals of the IEEE 1394 standard was to replace SCSI, which is covered in Book II, Chapter 5.

Don’t confuse IEEE 1394 (FireWire) with IEEE 1284 (mentioned in the “Serial and parallel ports” section, earlier in the chapter), which deals with bidirectional communication over the parallel port.

Although some disk drives have been implemented through the IEEE 1394 standard, it has seen the most growth in the area of data, voice, and video. Although many PCs have been shipping for the past few years with USB ports, IEEE 1394 has not seen the same level of adoption by the PC manufacturing industry. However, many device manufacturers support IEEE 1394 in their devices, and interface cards are readily available to be added to your PC.

FireWire is covered in Book II, Chapter 1.

Keyboard and mouse

Because you will certainly want to enter data into your computer, the keyboard connector on the back of your computer plays an important role. The two traditional types of keyboard connectors are P/S2 (or mini-DIN 6) and DIN 5. The mini-DIN connector has been the standard keyboard and mouse connector on computers for many years, but it faces being supplanted by USB. You should not be surprised if a new computer you purchase does not have a P/S2 connector for either the keyboard or mouse.

For details on connecting keyboards to your computer, review Book III, Chapter 2.

Monitor

You also need to see what you’re doing, so the monitor connector also plays an important role. With the demise of the MDA (Monochrome Display Adapter), HGC (Hercules Graphics Card), CGA (Color Graphics Adapter), and EGA (Enhanced Graphics Adapter) monitor types as well as the release of VGA (Video Graphics Array) and SVGA (Super Video Graphics Array) monitors, the monitor connector on the back of your computer changed from a DB-9 female connector to an HD (high density) DB-15 female connector. With the high adoption rate of LCD monitors, a new port is showing up on computers and video cards, supporting the higher throughput and digital signals that LCD monitors require. This port is a DVI (digital visual interface) port and accepts a monitor connector that has as many as 24 digital pins and optionally 5 analog pins (for backward compatibility).

You can read more about connecting monitors to your computer in Book III, Chapter 3.

Comparing Cable Types

In this section, you examine several different types of cables and discover the uses of each type. Some of the cables are used inside your computer, and others are external. After you complete this section, you should be able to identify the basic types of cables and where they are used.

Ribbon

Ribbon cables are often used to connect components inside a computer, such as hard disk drives and floppy disk drives. They are made up of several wires laid out parallel to each other in such a way that they resemble a ribbon, as shown in Figure 1-1. These cables usually have keyed connectors on them that prevent them from being incorrectly connected to devices. Note the small tab halfway down the edge of the connector: This tab matches a groove on the device that it is attached to. Note the blocked hole near the center of the connector: This hole matches a missing pin on the device that it is attached to.

You can read more about ribbon cables when connecting storage devices inside your computer, which is covered in Book II, Chapter 5.

Twisted pair

Twisted pair cables consist of three or four pairs of wires. The grading level is based on how the wires are arranged inside the cable, rather than the number of wires. In Figure 1-2, you can see how each pair of wires is twisted together at a specific rate, and then all the pairs are twisted together. This procedure reduces the effect of cross talk (interference) between the pairs of wires and interference from external sources. The differences between the different grades of cable include the quality of production material and the overall number of twists per pair of wires per foot of cable. Most networking is done with unshielded twisted pair (UTP) cable, which is more susceptible to interference but is more flexible — and, therefore, easier to work with than shielded twisted pair (STP) cable, which has a metal shielding over each pair of wires.

Table 1-1 provides a brief listing of the different types of twisted pair cables and their uses.

Table 1-1 Twisted Pair Cabling Types

Type	Usage
Category 1 (CAT1)	UTP cable designed for audio signal transmission. This wiring is intended to be used for transferring signals to speakers and other devices.
Category 2 (CAT2)	UTP cable used for low-speed transmissions. This wiring was designed for analog telephone applications. CAT2 cables can also carry lower-speed networking data, as in the case of 4 Mbps token ring networking.
Category 3 (CAT3)	UTP cable designed with data networking in mind. This category is similar in design to all the newer categories, but some electrical characteristics are unique to each. CAT3 cables carry 10 Mbps Ethernet data.
Category 4 (CAT4)	UTP cable was designed to carry 16 Mbps token ring data.
Category 5 (CAT5)	UTP cable designed to carry 100 Mbps Ethernet data. It also meets the requirements for 1000Base-T. CAT5e is an enhanced version of the cable that better meets the standards of 1000Base-T by reducing crosstalk.
Category 6 (CAT6)	A standard for UTP cable that supports frequencies of 250 MHz Ethernet data. CAT6a increases the frequencies that the cable supports and allows for data transfer rates up to 10 Gbps.
Category 7 (CAT7)	A standard for unshielded twisted pair cable that supports frequencies of up to 600 MHz. CAT7a increases the frequencies that the cable supports and allows for data transfer rates up to 100 Gbps.

You can read more about networking cables in Book VIII, Chapter 1.

Pay close attention to the uses of CAT3, CAT4, and CAT5 cable types because these map directly to network specifications. You will be tested on the minimum required cable type for 10 Mbps Ethernet and 100 Mbps Ethernet. As far as the industry goes, most new wiring is performed using CAT6 cabling.

Thick and thin coax

Thick coax is rigid, half-inch coaxial cable capable of carrying 10 Mbps Ethernet data a distance of 500 meters. Thick coax is also referred to as Thicknet or 10Base5.

Thin coax is a more flexible, quarter-inch coaxial cable capable of carrying 10 Mbps Ethernet data a distance of 185 meters. Thin coax is also referred to as Thinnet or 10Base2.

Coax is not used in many computer networks these days. If you see coax in a network these days, it is typically used to provide Internet service.

For more information about thick and thin coax use in computer networking, flip to Book VIII, Chapter 1.

Fiber

Fiber optic cable is so thin that it is measured in microns or micrometers (µm), or millionths of a meter (or, put another way, thousandths of a millimeter). Fiber optic cable for data networks comes in two core diameter thicknesses 50µm and 62.5µm. There are also cables that support a single communication mode or multiple communication modes, which refers to how light traverses the cable. Multimode cables can support distances as long as 1 kilometer (km), and single-mode cable can support distances as long as 140 km.

Fiber optic cable is also covered in Book VIII, Chapter 1.

Cable Orientation

Cable orientation refers to how two connectors fit together, so it could actually be referred to as connector orientation. More to the point, cable orientation defines how a cable connector attaches to another connector, which is usually on a computer or motherboard. Just about every time the term cable orientation is used, it refers to the internal ribbon cables used to connect serial ports, parallel ports, floppy drives, hard drives, and CD-ROM drives to a motherboard. Cable orientation is not usually used when discussing external connectors, which are used on the outside of your computer and tend to be able to connect only one way. The pins or holes on a connector are numbered, and hole 1 on a cable connector needs to match pin 1 on the computer’s connector.

The connector with the pins is the male connector, and the connector with the holes is the female connector. And even though the female connector does not have pins, the holes on the female connector are typically referred to as pins.

Internal cables (of course) are used on the inside of the computer. Some devices use unique cables, such as your sound card and CD-ROM drive. In many cases, these unique cables have Molex connectors (molded plastic connectors) that are usually keyed to prevent mistakes on connecting. A keyed connector is designed to connect only one way. You also see Molex connectors on the power leads that connect your power supply to devices, such as hard drives and the motherboard.

Remembering one simple rule can prevent most connection errors. On a ribbon cable, wire 1 connected to pin 1 has the colored (usually red or blue) stripe on it. This makes it easy to spot. On most devices that you are connecting the cable to, pin 1 is the pin closest to the power connector. This line or stripe was visible on the IDE cable shown in Figure 1-1.

Figure 1-3 shows two 40-pin IDE or EIDE connectors on the motherboard. Note that these are keyed and also have a small arrow pointing to pin 1. Most male connectors on the motherboard have a wall around the pins that has a slot, or key opening, that prevent errors — that is, as long as the cable you are using is also keyed. Keyed connectors on your cards or motherboard have a small notch cut from the side of the connector (in the middle of the long side of the connector in Figure 1-3), whereas keyed cables have a small lump or tab on them, which can be seen on the long edge of the connector (refer to Figure 1-1). The only way for the cable to be plugged into the connector is if the tab matches the notch, and there is only one way for that to happen — to line up pin 1 on your connectors.

If you recall, the IDE cable, specifically, has a second keying mechanism, which is the blocked hole. If you look closely at Figure 1-3, you should also see that one of the center pins is missing, matching up with the blocked hole on the cable connector.

EIDE is Enhanced IDE and should be considered to be an update of the IDE standard. There are many modifications of the basic IDE and ATA standards, but all use the same connectors on devices and controllers. Even devices following the UDMA (Ultra Direct Memory Access) standard use the same connectors but with an 80-wire ribbon cable. Regardless of the exact standards, each offer only minor alterations, so in general you can think of them all as Parallel ATA (PATA) drives; while Serial ATA (SATA) drives are a completely different standard. Most drives that you will be dealing with on new computers will follow the SATA standard. You can read more on the topic of drives in Book II, Chapter 5.

Connector Types

Many, many types of cables exist on the market these days: video cables, modem cables, printer cables, and extension cables, to name a few. Despite the many types of cables, there are very few types of connectors. The following sections look at the most common types of connectors that you will encounter.

IBM Type 1 connector

The IBM Type 1 connector is commonly used with IBM token ring networks, and will either connect the workstation to a hub or connect multiple hubs. Unlike typical connectors that are either male (with pins) or female (with holes) and must be paired with a connector of the opposite gender to allow them to be connected, the Type 1 connector can be connected to any other connector. IBM calls the connector a “hermaphrodite,” being composed of both genders of connectors. Figure 1-4 shows a Type 1 connector, with two connectors joined at the top of the figure.

DB-9

The DB-9 connector is a D-shell–type connector, so named because of their D shape. The DB-9 has nine connection points arranged in two rows. This connector used to be found on the back of a computer in its female form, to be used with a CGA or EGA monitor. Now, you’ll find a male DB-9 connector on the back of a computer as one of the two types of serial connections for COM ports. Figure 1-5 shows female and male DB-9 connectors.

DB-15

DB-15, also known as HD DB-15, has the familiar shape of the D-shell connector but contains a higher density (HD) pin arrangement, with three rows of five connection points rather than the traditional two rows. Typically used for VGA and SVGA monitor connections, look for this connector in its female form. Figure 1-6 shows the DB-15 connector.

DB-25

Once again, you see the familiar shape of the D-shell connector on a DB-25, but this connector sports 25 connections arranged in two rows. This connector is found on your computer in its male form in the role of a serial port and in its female form as a parallel port. You can also find the 25-pin male connector on the back of most modems. Figure 1-7 shows a parallel cable and a serial 9-25 pin converter; the latter is used to convert a 25-pin serial connector on the back of a computer down to a 9-pin port to be compatible with a 9-pin serial cable.

Centronics 36 and 50

A parallel cable has a DB-25 connector at one end and a 36-pin male Centronics connector at the other. You will find the female Centronics receptacle on your printer. Also, you will often see 50-pin Centronics connectors used with SCSI equipment, such as external disk or tape drives. Figure 1-8 shows 36-pin and 50-pin Centronics connectors.

RJ-11

RJ — short for registered jack — has small modular connectors that clip into matching holes. The RJ-11 connector is a standard modular connector used for telephones. It accepts four wires, usually in the form of a flat cable, rather than twisted pair cable. Analog telephone service is usually carried only on the two middle wires. You should see a female portion of this connector on your modem.

RJ-45

The RJ-45 connector — the larger cousin of the RJ-11 connector — usually accepts eight wires (four pair). This connector is used for 10BaseT, 10BaseTX, and token ring networking. (Basically, the RJ-45 is used anywhere UTP cables are used.) Officially, the RJ-45 connector was designed for voice-grade circuits, and what is now referred to as the RJ-45 is officially known as an 8-pin connector.

Do not confuse RJ-11 connectors with RJ-45 connectors. Figure 1-9 shows a RJ-11 connector on the left and a RJ-45 on the right.

BNC

The BNC (Bayonet Neill-Concelman) connector is used for Thinnet networking. (See “Thick and thin coax,” earlier in this chapter.) BNC connectors join with a male BNC that has a protruding point that fits into the female connector, and then a ring is turned on the outside edge to lock the connectors together much the same way that a bayonet attaches to a rifle (hence, the name). Figure 1-10 shows a BNC T-connector and a network card with a BNC connector.

BNC is also sometimes referred to as British Naval Connector — and a number of other names — but the actual name is a moot point for the exam.

BNC T-connectors are used to attach two Thinnet cables to a network card on the back of your computer. The T-connector has a male connector to attach to your network card and then two female connectors to accept the two Thinnet cables. A Thinnet network segment makes one long chain from all the computers that are on the segment by using T-connectors.

PS/2, or mini-DIN 6

The PS/2 (also known as the mini-DIN 6) connector is usually used for keyboards and mice for AT and ATX computers. This connector is now favored over the larger DIN 5 connector. Figure 1-11 provides a sample of the mini-DIN connector.

Universal Serial Bus (USB) connectors

USB 1.0, USB 2.0, and USB 3.0 all use proprietary connectors (shown in Figure 1-12) to connect as many as 127 devices. All these devices must be hot swappable (capable of being added or removed without turning off the computer off), thanks to the specification for the standard. These connectors represent the most common connectors used with USB:

Type-A connectors are used to connect to ports on your computer.

Type-B connectors are used to connect to ports on your devices, such as printers or hard drive enclosures.

With the advent of smaller and smaller USB devices, the device end of the cable has many smaller cousins, such as the mini-A, mini-B, micro-A, and micro-B connectors. Both mini and micro connectors have similar form factors that make getting your cables confused very easy. These connectors are found on many MP3 players, digital cameras, and cell phones.

USB 3.0 achieves its performance increase by using more wires in the cable to pass additional data. If you look closely at the USB 3.0 Type-A connector, you can see a second set of pins or contacts farther back in the connector. This allows connections to USB 3.0 ports on your computer to make use of the additional connections, while USB 2.0 ports will only make contact with the front contacts. This makes the connector backward compatible with USB 2.0 ports, without needing to carry around two sets of cables. On the device side, the USB 3.0 Micro-B connector has two sections, one that resembles a Micro-B connector and then a portion that makes use of the extra wires in the cable.

USB performance has improved over the years, as shown in Table 3-2, with USB 1.0 having a maximum speed of 12 Mbps and a maximum cable length of 5 meters (16.4 feet) when working with Full Speed devices; it was 1.5 Mbps and 3 meters (9.8 feet) for Low Speed devices. USB 2.0 raised the speed limit of devices to Hi Speed at a whopping 480 Mbps and a maximum cable length of 5 meters (16.4 feet). Finally, USB 3.0 has brought the speed limit up to Super Speed at 5 Gbps, and the cables have a practical limit of approximately 3 meters (9.8 feet).

By bringing the speed of USB up to 5 Gbps in USB 3.0 devices, a second option now exists for people who want to achieve maximum throughput for external hard drives. Prior to USB 3.0, eSATA was the preferred method for high-speed external drives.

Power may also be provided over the USB interface, with USB 1.0 and USB 2.0 providing up to 500mA and USB 3.0 providing up to 900mA. Standard USB controllers and ports are limited to only providing 100mA of power until the device requests more current, while some laptops and other devices have a charging port that will provide the maximum amount of power when a device is connected. This port is useful for supplying power to nonintelligent devices.

IEEE 1394 (FireWire) connectors

FireWire is an Apple Computer trademark for devices that match the IEEE 1394 specification. This specification allows 63 devices (without hubs) to be connected in a single bus. It also uses a proprietary connector, similar in size to the USB connector but with a different shape, as seen in Figure 1-13.

The IEEE 1394 standard in use falls into two categories:

1394-1995, also called FireWire or FireWire 400

FireWire 400, as the name suggests, is capable of sending data at 400 Mbps (half duplex) over a 4.5-meter cable (15 feet). Because FireWire allows 16 devices to be chained together, the total length of the chain could be as long as 72 meters (236 feet).

1394b-2002, also called FireWire 800

FireWire 800 improved on the FireWire 400 by allowing full duplex communications and throughput of approximately 800 Mbps.

Although the 1394b-2002 specification allows the use of fiber cables up to 100 meters (330 feet) long, most people rely on the shorter 4.5-meter (15-feet) standard cable and up to 62 devices in a chain.

Development work is still being conducted on the 1394 standard. But unless a big step forward in speeds is found, USB 3.0 will likely become the dominant standard for peripheral devices.

Standard External Cables

External cables are used on the outside of the computer to connect peripheral devices. The most commonly used connector on external cables is the D-shell connector (named for its shape), which is usually called DB. Looking at the connector with the D pointing toward the ground, pin numbering on male connectors starts with the top-left connector. With the connector in this orientation, the upper-left pin is pin 1, and the order goes across the connector and left to right for all subsequent rows. For a female receptor, hole 1 or pin 1 is in the top-right of the connector if the D is pointing down; other pins are numbered right to left. This allows pin 1 on a male connector to match pin 1 on a female connector. This section covers the three most common cables.

Parallel cable

A parallel cable has a male DB-25 connector on the end that connects to your computer, and a male Centronics 36 connector on the end that connects to the printer. This style of cable is a standard parallel cable or an IEEE 1284 bidirectional cable. If the cable is the latter, you should expect to see IEEE 1284 labeled on the cable or connector.

In addition to this cable, you might also see a parallel extension cable, which will have a male BD-25 connector to attach to your computer and a female DB-25 connector to attach to a parallel printer cable. This cable can easily be confused with a serial cable for a computer with a 25-pin serial connector. The only way to positively identify this cable is to use a multimeter or a ­continuity tester to see what pins on one end of the cable match which holes on the other end. For a parallel extension cable, this is a straight-though cable; and, each pin, 1 though 25, matches with the appropriate hole on the other end of the cable.

Serial cable

Numbering the pins on the connectors makes it easier to describe what the cable looks like at the connector level. This might make more sense when you look at the pin configuration for a standard 9-pin to 25-pin serial modem cable, and the 9-pin to 9-pin null modem cable in the next section. Modem cables are designed for a computer with either a male 9-pin connector or a male 25-pin connector, so the cable has either a female 9-pin or a female 25-pin connector on the end that connects to the computer, and a 25-pin male connector on the end that connects to the modem. Older computers have a 9-pin serial connector. The pin configuration and function for a 9-pin to 25-pin serial cable are summarized in Table 1-2.

Null modem cable

If you need to transfer data via serial ports between two computers that are close, use the same communications programs as if you were actually using modems and telephone lines to connect the computers. Such serial communication (that bypasses a modem) uses a null modem cable, which nullifies or eliminates the need for a modem by directly connecting the send and receive ports of the devices on either side of the cable. Table 1-3 shows how the pin connections are made between devices. If you look at the roles of the pins on each side of the connection, you can see that each pin that sends data is connected to the receive pin for that data on the other side of the cable, with the result that a transmit data pin is connected to a receive data pin.

Null modem cables are also used to configure many network devices, such as switches and routers, using a console port on the network device and a terminal communication program.

Viewing Cable Adapters

Many types of adapters can join different types of cables and devices. The following sections give a brief description of some of the major types.

Barrel connectors

The term barrel connectors comes from Thinnet networking, where cables could be extended by means of an adapter, resembling a small barrel, that accepted a male connector on either end. This term is now often applied to any connector that extends the length of a cable by joining two cables but that does not change the pin configuration. Figure 1-14 shows a barrel or cable connector for an RJ-45 cable.

Gender changers

Gender changers are a bit of a strange beast. They are straight-through connectors that don’t change the order or connection of the pins; they only change the sex of the connector that they are attached to. They look like a connector that has either two male or two female ends (as shown Figure 1-15); when attached to a cable of one sex, the connector becomes the other. These are used only in rare cases where your cables have the wrong sex connector, which is a situation that I often encounter with video connectors when working with KVM (Keyboard, Video, and Mouse) switches and cables made by different manufacturers.

Null modem

Null modem cables act as a replacement for two modems communicating with each other. If you have two computers that you want to connect directly, attach two modems and have one dial the other and transfer the files. Or, you can use a null modem cable. The null modem removes the modems from the equation and connects the send pins on one serial port to the receive pins on the other, and vice versa. If you don’t have a null modem cable, you can use a regular modem cable and a null modem adapter. The null modem adapter looks like a gender changer (see the preceding section) except that it changes the pin configuration as well as the sex of the connection. To tell whether you have a null modem adapter or a gender changer, look for a label, or check the pin configuration on either end of the adapter by using a continuity tester or multimeter.

Multimedia Connectors

Multimedia is one of the new hot areas of computers and how people are using them. Several standard types of connections are used for multimedia purposes. Table 1-4 provides some standard multimedia connectors and their uses. Analog audio purists may laud the slow or continuous change in tones from an analog sound system, resembling the smooth sine wave. But for computers that process everything in harsh 0s and 1s, the boxy digital signal is easier and faster to process. If you can avoid the translation between analog and digital signals, you should.

Table 1-4 Types of Multimedia Connectors

Role	Connectors Used
Analog audio	The main analog audio connector used in your computer is the one-eighth-inch connector, which is the standard headphone, speaker, and microphone jack for most sound cards. This form of connector has been around for years as an audio connector.
MIDI	The Musical Instrument Digital Interface (MIDI) connector has been in use since the 1980s, but the standard for it was finalized only in the early 1990s. Most electronic keyboards and many other instruments have MIDI connections on them, which are usually 5-pin DIN connectors; the connector on a computer is a DB-15 connector. MIDI connections allow for time synchronization, sequencing, recording, editing, and playback of MIDI-formatted data. The MIDI file format is extremely efficient.
Analog video and cable	Computers make use of the same video transfer cables used in the home AV market. These include coaxial cable that can carry audio and video signals; RCA cables that can carry either an audio or video signal (but, if you have an RCA connector on your computer, it is likely a yellow video connector); and S-Video, which is used for higher quality video signals and uses a mini-DIN 4 connector. These cables are used to connect your computer to a variety of video devices to either capture or display data.
Digital audio	The main digital audio connection for your computer is a S/PDIF (Sony/Philips Digital Interface Format) connection. Many motherboards and soundcards support this interface for multimedia applications. The S/PDIF connection is often made using coaxial, RCA, or optical connectors and cables.
Digital video	The home video market has standardized on the HDMI (High-Definition Multimedia Interface) video connector type. This 19-pin connector is capable of providing both video and audio signals. With its popularity, you have seen it become adopted by the computer industry for both multimedia and nonmultimedia computers, giving people a wider variety of output devices. HDMI uses the same video signaling as DVI, which makes it very compatible with computer displays, while providing superior performance characteristics when compared to VGA. Also, remember that VGA is analog, while HDMI is digital.

When looking at digital video solutions, there are a few additional facts that you should be aware of:

HDMI connections support sending audio signals over the connection, in addition to digital video signals.

HDMI supports only digital signals, while DVI has backward support for analog signals.

DisplayPort is a new royalty-free digital video standard. While it is not compatible with DVI or HDMI, the newer DisplayPort++ ports can be used with an external adapter to provide video signals to DVI and HDMI devices. Analog signals cannot be provided without an external converter.

DisplayPorts are similar in dimensions to HDMI, making them less than half the size of VGA or DVI ports, and very useful on mobile devices.

HDMI and DisplayPort both have smaller port designs, which are used on tablets and other small electronics; HDMI standards are supported on mini-HDMI, while DisplayPort standards are supported on mDP (mini DisplayPort).

If you have been working with DVI connectors for a while, you may have noticed that they are not all the same. Figure 1-16 shows the main variants of DVI connectors, while their uses include the following:

DVI-I (single link and dual link): The I in the name is for integrated, as this port type supports digital and analog video signals over the same connection, allowing either type of monitor to be connected. Dual-link connectors send twice the video signal, allowing them to be used on large high-performance displays or over a longer distance. Analog signal support is provided by the four pins on the left of the connector and needs an adapter to support the standard 15-pin VGA connection.

DVI-D (single link and dual link): The D in the name is for digital, as this port type supports only digital video signals. Again, this port type has single-link and dual-link variations.

DVI-A: The A in the name is for analog, as this port type supports only analog video signals and is used for connections to analog monitors through an adaptor.

Mini-DVI and micro-DVI are two small form factor DVI connectors, which Apple has used on its laptop lines. These connectors are not widely used.

Getting an A+

In this chapter, you examine the role of different types of connectors. In the process, you discover the differences between serial and parallel communication, as well as the differences between USB and IEEE 1394 (FireWire). You find out about the different types of cables and connectors that are used in different areas of a computer system. You should now have a general understanding about where and why different cables and connectors are used in your system.

Prep Test

1 Which of the following ports offers the fastest throughput or transfer speed?

A Serial

B Parallel

C USB

D IEEE 1284

2 What type of connector on the back of your computer accepts a parallel cable?

A DIN-8 female

B DB-25 female

C DB-9 female

D DB-25 male

3 What type of port uses a three-row DB-15 connector?

A Serial

B SVGA

C Parallel

D Game

4 RS-232 is a term associated with which type of port?

A Serial

B Parallel

C SCSI

D Game

5 Ethernet network cards typically use what type of connector?

A RJ-32

B DB-9

C DB-25

D RJ-45

6 BNC connectors are usually used on your computer to provide which of the following?

A Serial connections

B Parallel connections

C Networking

D Never used

7 How is serial data moved?

A Across multiple cables at the same time

B As a sequential stream of data

C Using a bidirectional information algorithm

D Using multi-clock sequencing

8 Data transfer speed for the IEEE 1394 standard is

A 10 Mbps

B 100 Mbps

C 400 Mbps

D 12 Gbps

9 Monitors usually connect to a computer through what type of connector?

A DB-15

B DB-25

C USB

D RS-232

10 CAT5 cables are defined by which of the following?

A Number of pairs of wires

B Length of the cable segment

C Type of shielding that is used

D Number of twists per foot in each pair of wires

11 Thin coaxial cable usually implements which type of connectors?

A BNC

B RJ-45

C RS-232

D IEEE 488

12 Pin 1 on a ribbon cable is usually identified by what?

A The number 1 inscribed on the connector

B A colored line on the wire leading to it

C A keyed connector

D Pin 1 is always on the left side of the connectors

Answers

1 C. USB offers the highest transfer rates. USB 1.1 has transfer rates of 12 Mbps, USB 2.0 offers transfer rates of 480 Mbps, and USB 3.0 offers transfer rates of 5 Gbps. This question might have been disputable if IEEE-1394 (FireWire) had been in the question because it has transfer rates of 400 Mbps. See “Universal Serial Bus (USB).”

2 B. On the back of your computer, the parallel port has a DB-25 female connector. Review “DB-25.”

3 B. VGA and SVGA use HD DB-15 connectors that have three rows of five pins. Take a look at “DB-15.”

4 A. RS-232 is one of the standards associated with the serial port. Peek at “Serial and parallel ports.”

5 D. RJ-45 is typically used for networking. Look over “RJ-45.”

6 C. BNC connectors are used for Thinnet or 10Base2 networking. Study “BNC.”

7 B. Serial cables move data sequentially, one bit at a time, and parallel cables allow for all 8 bits to be sent at one time. Refer to “Serial and parallel ports.”

8 C. FireWire, or IEEE 1394, allows for transfer rates up to 400 Mbps. Examine “FireWire (IEEE 1394).”

9 A. VGA and SVGA monitors usually connect to your computer via a high-density DB-15 connector. Review “DB-15.”

10 D. CAT5 cables are defined by the type of copper wire that is used and the number of twists per foot by each pair of wires. Check out “Twisted pair.”

11 A. BNC connectors are used with Thinnet Ethernet networking. Peruse “BNC.”

12 B. Pin 1 is identified by a colored line on the side of the cable that contains Pin 1. Keyed connectors prevent you from putting the cable in the wrong way but do not specifically identify pin 1. Take a look at “Ribbon.”