Ports and Connectors

Legacy Multifunction Ports :- Every cable has a connector at the end that plugs into a corresponding port on a PC. Connectors carry data and sometimes power between devices attached to the PC. Ports are the interfaces, the “doorways” used to connect devices to the PC. Connectors and ports can be either male or female, defined as having pins or sockets, respectively.

Let’s start with the two ancient multifunction ports that linger on most modern PCs: serial ports and parallel ports. Serial and parallel ports have a slight D shape, which allows only one proper way to insert a plug into the socket and makes it easier to remember what they’re called. Technically, they’re known as D-sub or D-subminiature connectors, but most techs call them DB.

Serial Ports :- Serial ports come in 9-pin and 25-pin varieties (Figure1-1). Of the two, the 9-pin (five pins on the top row, four on the bottom) variety is much more common, although even those are rapidly disappearing from modern PCs. Serial ports transfer data 1 bit (the smallest unit of data in the PC world) at a time, with a maximum throughput speed of 115 kilobits per second (Kbps). 

A 25-pin serial port and a 9-pin serial port

Devices that connected to the PC via the serial port included mice, external modems, label printers, personal digital assistants (PDAs), and digital cameras.

All devices in a PC get assigned certain system resources, and serial ports are no exception. The CPU uses input/output (I/O) addresses to give commands to devices; some devices use an interrupt request (IRQ) to contact the CPU. Most motherboards have at least one serial port—appropriately called Serial Port 1. By default, this port gets assigned the I/O address 3F8 and IRQ 4 (COM1).The rare Serial Port 2 on a PC gets I/O address 2F8 and IRQ3 (COM2) by default. You can use the CMOS setup utility to change the resources assigned to devices built into the motherboard—such as serial ports. Further, you can enable or disable the serial port(s) in the CMOS setup utility to free up resources, although you’d need to do this only on old computers. 

Parallel Ports :- Parallel ports are the 25-pin (13 on the top row, 12 on the bottom) female ports on the back of older PCs, as shown in (Figure1-2). Folks often incorrectly refer to parallel ports simply as “printer ports,” but many other devices have used parallel ports, such as external CD-ROM drives, Zip drives, and scanners.

A 25-pin parallel port

Printers that connect to parallel ports on the PC have a centronics port rather than a parallel port. Centronics connectors have a central tongue with contacts rather than pins, and come in two varieties. The more common is the 36-pin IEEE 1284B connector; the rarely used variety is the mini centronics IEEE 1284C connector.

IEEE 1284B centronics connector and port

IEEE 1284C mini centronics connector

Note :- IEEE IEEE stands for the Institute of Electrical and Electronics Engineers, the international organization that creates standards for electrical things, such as ports, cables, and connectors. You’ll see them again later in this chapter.

Parallel ports traditionally get I/O address 378 and IRQ7 (LPT1), but as with the serial port assignments, modern motherboards give you the option of changing this setting. Technological advances, such as the Extended Capability Port (ECP) and the Enhanced Parallel Port (EPP), offer improved throughput, to about 10 times faster than a standard parallel port.

Standard Single-Function Ports :- Every PC sports several single-function ports for connecting peripherals such as keyboards, monitors, and the like. With only a couple of exceptions, these standard ports support only a single type of device.

Keyboard Port :- Keyboards come in a variety of styles, from the plain-Jane, rectangular typewriter substitute to the exotically curved, multifunction gadget that’s bristling with special function hotkeys and equipped with ports of its own. Regardless of their appearance, however, all keyboards enable you to do one thing—enter commands into your PC. Modern PCs have a purple 6-pin mini-DIN (commonly called a PS/2 connector) port (Figure 1-5). The mini-DIN port is keyed so you can insert the keyboard connector only one way.

Mouse Port :- Like keyboards, mice come in an array of sizes and shapes, and they use a variety of connectors to attach to the PC (see Figure 1-6).All mice enable you to manipulate the operating system (OS) and applications.

Traditionally, mice plugged into one of the serial ports on the back of the PC, but most motherboards today have a dedicated mini-DIN mouse port. Aside from color, the green mouse port appears identical to the purple PS/2 keyboard port, but they’re not interchangeable.

You can plug a PS/2 mouse connector into a PS/2 keyboard port, and vice versa, but they won’t work. Mice go into mouse ports—keyboards go into keyboard ports. Some portable computers have a single black or gray mini-DIN port that can handle both a mouse and a keyboard (though obviously not at the same time!).

Video Ports :- Standard cathode ray tube (CRT) monitors and many projectors connect to your PC using a 15-pin D-subminiature connector arranged in three rows of five pins each. The corresponding video port on the PC, as shown in Figure 1-7, accommodates only that connector. No other port on your PC looks like this one. Many flat-panel liquid crystal display (LCD) monitors and some projectors use a specially keyed, 24-pinDigital Visual Interface (DVI) connector that plugs into a DVI port on the back of your video adapter card, as shown in Figure 1-8. DVI comes in several varieties, such as analog, DVI-A, and digital, DVI-D.

Note :- Thin-film transistor the most common LCD monitors use a technology called thin-film transistor (TFT). Many techs erroneously refer to all LCD monitors as TFTs.

Audio Ports :- At one time, audio was considered an extra add-on, but sound is standard issue on modern PCs. Most audio ports take the form of the popular 1/8” mini-audio connectors commonly seen on the Sony Walkman or other similar gadgets. A PC typically has at least three color-coded sound ports: a green speaker output port, a pink microphone input port, and a blue auxiliary input port, as shown in Figure 1-9. Better audio systems offer more jacks for rear speakers, center speaker, and subwoofer.

Multimedia Ports :- The convergence of television, music, and the computer has many newer PCs sporting various multimedia connectors. Some of these connectors, such as the RG-6 coaxial connector, have been around for a long time. The RG-6 connector sits on the video card or a dedicated TV tuner card and enables your PC to receive video and audio signals from a cable company or video cassette player. Other older connectors include S-Video—for sending video content from the PC to the TV—and composite connectors—for connecting left- and right-channel audio and a single video source into or out from the PC. Figure 2-11 shows an ATI All-in-Wonder card with the many multimedia connectors it offers.

MIDI/Joystick Ports :- Older PCs have an integrated female DB-15 port for connecting joysticks or other game controllers. These ports also support MIDI devices, such as a music synthesizer keyboard, although you need a special breakout box to make the MIDI connection. Unlike DB-15 video connectors, MIDI/Joystick connectors have pins arrayed in two rows, with eight on the top and seven on the bottom.

Modem Ports :- PC modem ports look identical to female telephone jacks and use standard, two-wire RJ-11 telephone cables and connectors (Figure 1-14). The locking clips on the male RJ-11 connectors secure the cable into the port. Most modems also have an output port for a telephone.

Network Interface Ports :- Network interfaces come in two main varieties. Most network interface cards (NICs) and motherboards have an eight-wire RJ-45 port (Figure 1-15). RJ-45 connectors look like wider-than-normal RJ-11 telephone connectors and plug into the female RJ-45 ports in the same manner that RJ-11 telephone cables plug into a modem. High-end NICs have two fiber connections (in/out) of one variety or another. The most common fiber connectors are the SC-ST and the LC-LC 

Note :- NIC Network interface cards (NICs) enable PCs to connect to a network. Techs call them NICs even when the network adapter is built into a motherboard and thus distinctly lacking in “card-ness.”

Modern Multifunction Ports :- Modern PCs use one or more multifunction ports to supplement or replace the aged serial and parallel ports. All newer machines have universal serial bus (USB) ports; many have IEEE 1394 (FireWire) ports; and a few have a small computer systems interface (SCSI) port. All three come in at least two varieties and can be used to connect everything from printers to digital cameras.

USB :- USB comes in two flavors, USB and Hi-Speed USB. Regular USB—often mistakenly called USB 1.1—devices transfer data at speeds of 1.5 or 12 megabits per second (Mbps), making them much faster than parallel or serial communications. Hi-Speed USB is faster still, capable of bursts up to 480 Mbps. Note that despite the huge difference in speeds, Hi-Speed USB technology is fully backward- compatible with regular USB devices. You can plug a regular USB device into a Hi-Speed port, in other words, and it will work.

Note :- USB 1.1 All current USB devices fall into the USB 2.0 specification. The initial specification that came to market was called USB 1.1 and matched the data throughput and connections of the current USB 2.0 (not Hi-Speed) devices. Many techs and consumers continue to use the term USB 1.1 to describe the lower speed USB 2.0 devices. Some marketing materials distinguish between 1.5 and 12 Mbps USB devices as USB and Full-Speed USB, although the latter term is not used in the specification at all.

USB ports come in three varieties, A, B, and mini. All are female and rectangular- shaped. The four contact pins are mounted on a plastic protrusion that keeps you from inserting the USB cable improperly. You plug the flat USB A connector into the corresponding port on a PC or USB hub—a generic term for a device with multiple USB ports (Figure 1-17).Most bigger peripherals, such as printers and scanners, have a B port into which you’d plug a B connector (Figure 1-18). Small USB devices, such as digital cameras and music players, use the mini port. Figure 1-19 shows a mini USB port and connector.

You can also find USB extenders. These have a USB A port on one end and a USB A connector on the other. You can use these for extending a mouse or keyboard cable and for connecting wide USB a device—such as thumb drives—to portable computers. Many current devices, such as keyboards, mice, joysticks, microphones, scanners, printers, modems, PDAs, digital cameras, lap warmers, cup heaters, personal fans, lamps, and more, connect to the PC via USB.

IEEE 1394 :- IEEE 1394 is an exciting communications technology created in a joint effort by Apple Computers, Texas Instruments, and the IEEE organization. The IEEE 1394 standard has been widely adopted not only by computer and peripheral makers, but also by manufacturers of home electronics such as digital video recorders.

Different manufacturers market IEEE 1394 technology under different trade names, such as FireWire (Apple), iLink (Sony), or Lynx (Texas Instruments), but they all refer to the same thing. Of these terms, FireWire is the most popular term among techs.

Note :- FireWire, iLink, and Lynx The terms FireWire, iLink, and Lynx all refer to the IEEE 1394 interface.

The original specification for FireWire—1394a—calls for data transfers of up to 400 Mbps. The current generation of FireWire—1394b—is capable of speeds up to a blinding 800 Mbps. What’s even more impressive is that the design spec for FireWire states that speeds of up to 1600 Mbps are possible. FireWire technology is a very good match for video, external hard drives, backup storage devices, and other hardware that needs real-time data access. Connecting FireWire devices together enables them to communicate. Running a FireWire cable between two PCs, for example, creates an instant point-to-point network for sharing files. You can connect up to 63 FireWire devices together in a daisy chain, although you would need devices that came with their own power supply to use that many. One cool feature of FireWire chains is that you can use a device somewhere down the chain even if one or more devices in between the port and device is powered down.

The 6-pin standard FireWire 400 ports are slightly taller than USB ports and rounded on one end. The connector plugs are of course shaped to fit, as shown in Figure 1-20. Some devices, such as digital camcorders, use a 4-pin mini- FireWire connector, similar to the mini-USB connector, although they are certainly not interchangeable (Figure 1-21). FireWire 800 devices use a square 9-pin connector (Figure 1-22). You can get adapters and two-headed cables to connect a FireWire 400 device into a FireWire 800 port.

SCSI :- SCSI—amusingly pronounced “skuzzy”—has been around for a long time. Innovations in SCSI technology have kept SCSI competitive with other enhanced technologies such as USB and FireWire. Many high-end PCs have built-in SCSI connectors, and SCSI controller cards are widely available to add SCSI ports to your system. SCSI devices have a variety of interfaces—SCSI-1, SCSI-2, Ultra SCSI, Wide Ultra SCSI, just to name a few—but the 68-pin female Ultra-320 port shown in Figure 2-23 is the most common today. You may also see 50-pin or 25-pin ports on some older devices or PCs. Note that the very fine port sockets shown in the picture are matched to fine contact pins on the male Ultra-320 connector. Take it from me, these tiny pins bend and break easily, so handle with care! Data throughput on SCSI varies from around 5 to 80 megabytes per second (MBps) for early incarnations to 320 MBps for many current versions. 

Check yourself 

Legacy Multifunction Ports :- The 9-pin and 25-pin serial ports and the 25-pin parallel ports are used for connecting serial and parallel devices, respectively, to the PC. Serial devices transfer data 1 bit a time, whereas parallel devices transfer data 8 bits at a time.

Standard Single-Function Ports :- Keyboards connect to the motherboard with 6-pin mini-DIN (PS/2) or USB connectors. Mice connect to the 9-pin serial bus in older systems, and PS/2 or USB in newer systems. Make sure you remember the 15-pin, three-row D-sub port is for video, whereas the 15-pin, two-row D-sub port is for MIDI devices or joysticks. Finally, know the difference between the RJ-11 connectors for modems and the RJ-45 connectors for NICs.

Modern Multifunction Ports :- USB enables you to hotswap devices and daisy-chain up to 127 devices in one PC. The Type A connector goes into the USB port; the Type B or mini connector goes into the USB device. USB (a.k.a. normal USB 1.1) is capable of throughput speeds up to 12 Mbps,whileHi-Speed USB is good for up to 480 Mbps. IEEE 1394 is also known as FireWire, iLink, and Lynx. The 1394a version is capable of speeds up to 400 Mbps, and 1394b runs at up to 800 Mbps. Either version of IEEE 1394 enables you to connect up to 63 devices to a single IEEE 1394 port. Finally, the 68-pin ports used by Ultra-320 devices are the most common ones seen on the many 

SCSI technologies available today, but you might also see 50-pin, 25-pin, or other varieties.