Ports & Connectors

Ports & Connectors
The various connectors and ports on the computer allow it to communicate with the many different devices and peripherals attached. Because there are so many cables and cords attached to the back of the computer, and so many different types of connectors, it often seems a little intimidating to the newer user. Although there are some devices which may use the same connector or port, the individual devices and their cords can only physically attach to one certain type of connector; so don't feel nervous about hooking your system together.

There's really no way you can do any harm to your computer just by hooking it up, as long as you follow a few common sense rules:

The first thing to know is the difference between a male and female connector. The male connector fits inside the female connector. If the connector has pins protruding from it, its a male connector. If the connector has holes for the pins to fit into, then its a female connector. When you hook something up to your computer, the male and female connectors are hooked together. The connectors on the back of your computer are called input/output ports (i/o ports) or communication ports.

The second thing you should remember is that when you join a connector to a port, they must have the same shape and the same number of pins or holes. In other words, a square peg won't fit into a round hole, and its not wise to try to jam fifteen pins into nine holes (part of the 'common sense' thing I was talking about).Which brings us to another very important point, never force anything.

Here's one that's hard to do. Always make sure the computer is off before attaching connectors or cables to any of the ports. This can cause little power gliches (another technical word) that could corrupt an open file or cause a program to freeze. It can even cause a small short that could damage or ruin components inside your computer. I know, you've done it a hundred times and never had a problem. Well, that's good. If you want to continue to practice risk management, that's your perogitive, but be aware of the possibilities and don't be surprised when you finally get burned. USB ports are the only ports that should be considered hot-swappable (this means they can be plugged in or unplugged while the machine is on).

Only one more thing to remember. There are small hexagonal nuts on either side of many of the ports on your computer. These allow you to screw the connectors in so they don't accidentally fall out or loosen. They just have to be screwed down, they do not have to be tightened. These nuts are actually the heads of small bolts that pass through the back plate on your computer and are attached with a small nut on the other side. If you tighten the screws too much, then when they're undone, they may take the bolt with them and the small nut may fall off inside the computer (onto the motherboard or an expansion card). Not a good thing.

Now that we know the basic rules, let's take a look at some of the connectors or ports you might find on your computer.

DB Connector
The most common connector is the DB connector. It's sort of a 'D' shape and is sometimes called a D-shell connector (go figure). It's designated as DB-x, with 'x' being the number of pins or holes on the individual connector. So a DB-9 female connector would be a 'D' shaped connector with 9 holes. This would receive a cord with a DB-9 male connector (with 9 pins).

If you find a DB male connector port on the back of your computer, (either a DB-9 male or a DB-25 male) it's going to be a serial port. Serial ports are also called COM ports or RS-232 ports (Reference Standard #232 as referenced by IEEE*). Serial ports transmit data one bit at a time and are relatively slow compared to other ports. However, they are plenty fast enough for some external devices such as a mouse, or an external modem. Because only one bit at a time is passed along a serial cable, it can travel a fair distance before data integrity is challenged (or errors start to occur). A serial cable shouldn't be more than 50 feet in length.

Incidentally, in case you were wondering, if you have a device with only nine holes on its connector, and only a DB-25 male serial port to connect to, all you need is a 9 to 25 pin adapter. There's no difference between a 25-pin serial port and a 9-pin serial port other than the fact that the DB-25 male has sixteen extra pins that it doesn't use.

If you have an older computer, and see a DB-9 female connector on the back, it's probably a video connector for an older EGA or CGA monitor. My guess is that you won't see one on your computer. However, if the question should ever come up, it could also be a Token Ring network adapter port.

Look on the back of your computer, you may be able to find two different DB-15 female connectors. If you see three rows of five holes, then it's your VGA or SVGA video monitor adapter. If you see only two rows (one of eight holes and one of seven), then it's probably a joystick adapter.

A DB-25 female connector on the back of your computer is going to be a parallel port. Parallel ports can transmit data eight bits at a time which creates a noticeable speed increase over serial ports. Most commonly used as printer connections, several other devices now use the parallel port such as tape backup systems, Zip drives and scanners to name a few. These devices are generally fitted with what is referred to as a pass-through port. This means that you can hook up your scanner to the parallel port (DB-25 female) and then connect your printer to the DB-25 connector on the back of the scanner and have access to both devices. This usually works well but does pose some problems. First off, the device has to be turned on for the pass-through port to work. To take this one step further, the device often has to be turned on before the computer is booted, to be recognized properly and for the right drivers to be loaded at startup. Also, users tend to think that they can daisy-chain these devices. In other words, connect their scanner to the computer, attach their Zip drive to the back of the scanner, their tape drive to the back of the Zip drive, and then their printer to the pass-through port on the back of the tape drive. Believe it or not, I've seen this done and I've seen it work (more or less). I've also seen it work one day and not the next. It's a hit and miss sort of thing (more miss than hit) and I wouldn't trust the integrity of the data past the second device.

Another thing to keep in mind, is that the cable on a parallel device shouldn't be more than 10 feet long. Data errors can occur beyond this distance.

DIN Connector
The DIN connector is a small round connector, usually with a keyed slot for proper orientation. Again, it's designated as DIN-x, with 'x' representing the number of holes or pins on the connector. It comes in a couple of different sizes and it's been used on computers about as long as the DB connector has. It's a fairly popular connector because of its small size and solid connection.

The most common DIN connector would have to be the DIN-5 keyboard connector. Its the largest of the DIN connectors that you're going to find on your computer and its been around for a long time. If you own a newer computer, then the DIN-5 has probably been replaced with a DIN-6 (mini-DIN or PS/2) connector.

The PS/2, or DIN-6 connector, was mainly used by Macintosh computers for the longest time (Macintosh also used a DIN-8 connector for their printer). You may hear them referred to as a mini DIN-6 connector. They're smaller and more compact than the typical DIN-5 connector and have become the standard for both the keyboard and the mouse on newer PCs. If this is the case on your computer, then the two DIN-6 female ports on the back of your computer are going to look an awful lot alike, and you need to distinguish between the mouse port and the keyboard port before hooking them up. They may be color coded or they may have a little icon beside them representing their use. Whatever the case, you're not going to do any harm if you accidentally get these two devices switched. Your mouse won't work, or you'll get a keyboard error at boot up. Your first course of action for troubleshooting this type of problem should be to check the connection anyway.

Another port you could find on the back of an older computer is the DIN-9. It would be another mini DIN port with 9 sockets. A bus mouse or a hand-held scanner may use this type of port, but it's unlikely that you're going to find one on a newer computer.

RJ Connectors
The RJ connector is used for communication devices. If you live in North America and have a jack on your wall that your phone connects to, that's an RJ-11 connector. Now, the RJ-11 connector or port doesn't have 11 pins or 11 holes. As a matter of fact, it only connects 4 or 6 wires.

You may have an RJ-11 connector on the back of your computer if you have an internal modem. This is to hook a phone line up allowing communication with other computers and access to the Internet and the World Wide Web.

If you see two RJ-11 connectors side by side, it means that you can hook the phone line to your computer using the one jack, and then an extension phone can be plugged into the other jack. A lot of modems today allow for fax and voice capabilities. This means that you can fax from your computer, it can double as an answering machine that records messages and voice mail, and, if you have speakers and a microphone, you can even use it as a speakerphone.

An RJ-45 connector looks much like the RJ-11, only larger. It connects 8 wires and is used for network ethernet connections. If you see and RJ-45 connector or port on the back of your computer then there's two possibilities; Your computer is hooked up to a network or intranet, or, you have cable hookup to the Internet and the World Wide Web. The latter uses an RJ-45 connection between the cable modem and the network interface adapter (which is the same adapter you would be using for a network connection).

As you can see, the RJ connector is designated as RJ-x. But the 'x' doesn't tell you the number of connectors that the port has like other ports. At one time, I thought it might designate the size of the jack. The RJ-45 is larger than the RJ-11, but the RJ-12 is smaller (this is the connector between your phone and the handset), so I guess that doesn't hold water either. At this point, I become disinterested... If you know the answer, let me know and I might change this paragraph. But mainly what you need to know is, the RJ-11 connects 4 or 6 wires, is used on modems and telephones, and is smaller than the RJ-45 which is used for ethernet connections to network interface cards.

Centronics Connectors
The Centronics connector is a parallel interface connector. It has eight parallel data lines which allow data to travel eight bits at a time. (remember the parallel DB-25 female port). The Centronics connector is designated as Centronics-x, with 'x' representing the number of teeth or connections it has. It kind of looks like an elongated DB connector with metal teeth as connectors instead of pins. Some connectors have small clips on either side to hold it in place.

You're probably not going to find this connector on the back of your computer, but on the opposite end of your parallel cable where it connects to the printer. This will more than likely be a Centronics-36 connector.

If you have SCSI or know what SCSI is, then you should know that SCSI can use a Centronics-50 or Centronics-68 connector, as well as a DB-25.

USB (Universal Serial Bus)
Universal Serial Bus is a relatively new connector that was meant to replace Serial and Parallel ports. Its a flat, keyed connector with four contacts that was designed for mid-speed peripherals such as scanners, keyboards, mice, joysticks, printers, modems and some CD-ROMs. USB is unique in that it is completely hot-swappable. In otherwords, you can plug it in or unplug it while the computer is on. Your computer should recognize it as soon as its plugged in, and you should have use of the device immediately.

USB allows you to daisy-chain up to 127 devices. This means that you could have a joystick plugged in, with a printer plugged into that, and a scanner plugged into the printer, etc...

USB was first introduced with new computers around 1997 and the final version of Win95 (SR2) provided very limited support for it. A few problems seemed to develop at first. You had to have a Pentium machine with a BIOS that supported USB, and it had to be enabled in the setup. Your computer had to have USB ports on it, or pins that allowed for the attachment of a USB interface. Aside from that, you could install a USB adapter card in one of your PCI slots. Then, there weren't a lot of USB devices out there.

I think one of the biggest problems that arose at first was that people weren't using the proper Operating System. The early versions of Win95 did not support USB. Also, a lot of machines shipped with USB ports or capabilities before the BIOS supported it completely. Updating, or flashing the BIOS could sometimes solve the problem.

Despite the growing pains, Windows 98, and computers shipped after 1998 provide excellent support for USB; and the number of devices have increased dramatically.

I have a USB mouse and scanner that I can hot swap between my desktops and my laptop with immediate access. To tell the truth, I haven't even tried daisy-chaining together, and as I write this, I'm thinking about going out and buying a keyboard just so I can try it. I think USB is fantastic, and I'm looking forward to the day when all peripherals are that easy to install and configure.