While the Universal Serial Bus (USB) has become the way to connect most devices to a computer, there are several other connections available on most systems. Here is a breakdown of what they look like and what their function is:
1) The Joystick/Game Pad Port
This port allows older, non-USB joysticks, game pads and other controllers to be connected to a computer. It is often found coupled with the audio card.
2) USB ports
These ports come in two varieties: The older 1.1 (11Mb/s) and newer 2.0 (over 350 Mb/s). Some computers have a pair on the back and another pair on the front of the case. The sample shown at the right is actually an add-on 2.0 card on a machine that only came with slower 1.1 ports.
3) The Small Computer System Interface (SCSI)
This is a fast multipurpose connector that can be used to connect external drives, scanners and other devices to a computer. These were common in Macintosh computers for many years. They are still in use by many systems for large hard drive arrays that need transmit data quickly to many computers on a network. For home users, this is yet another connection that has been essentially replaced by USB.
4) IEEE 1394 (Firewire) Interface
This is a very fast digital interface often used for moving video between a digital video camera and a computer. Some external hard drives also use this interface. However, due to it's higher speed and common interface, USB 2.0 is slowly taking over this area, too. The one gotcha in this area is firewire tends to have a better sustained speed than USB 2.0. This is because USB runs through more components of the system than firewire does. Under load conditions, firewire will almost always win out in sustained speed.
5) Audio Connections
These are located on the audio card, which may be an add-on piece of hardware or built into the motherboard. Most audio cards include a microphone input, a headphone jack and a line out jack for connecting speakers to your system. Some systems include a line in jack for better quality audio recording from certain devices.
6) The Mini DIN or PS2 Keyboard Port
This port replaced the serial port as the method of connecting keyboards to computers. It contains 6 pins and usually has a blue color ring on it to correspond to the color of the keyboard plug. Most newer keyboards use USB connections.
7) The Mini DIN or PS2 Mouse Port
This is a plug that is identical to the keyboard connector listed above, except it is intended for the mouse. It is usually color orange to correspond to the mouse plug. Most newer mice use USB.
8) The Ethernet Jack
This is a wired networking connection used to connect multiple computers or connect to a broadband Internet service. Though the wired versions are usually faster, many people prefer the freedem of Wireless (or WiFi) Ethernet connections to allow computers to be easily moved and to avoid running a lot of network cabling.
9) The Serial Port
This is the interface that keyboards, mice and modems once used to connect to a computer. These ports were later replaced by the PS2 interface, which in turn are quickly being replaced by USB. Other than certain diagnostic devices, backup batteries and other holdouts, this port is all but useless.
10) The Parallel Port
This is a coonection that can be used for printers as well as some other devices, like external floppy or Zip drives. Devices that use this port have mostly been replaced by those that use USB connections. With the right adapter, even parallel port devices can be used with a USB connection.