In a computer there are various connectors and ports, which help in establishing a communication path between the CPU and the various above mentioned Storage devices. Before learning about the various available connectors, it is essential to be familiar with the following terms :
1. Cable is a wire
2. Socket is the female side of a connector.
3. Pin is the male side of a connector.
4. Port is generally a place for physically connecting to some other device usually with a socket.
PC Ports
1. Parallel Port
Parallel ports can be used to connect a host of popular computer peripherals like :
- Printers
- Scanners
- CD burners
- External hard drives
- Iomega Zip removable drives
- Network adapters
- Tape backup drives
Parallel ports were originally developed by IBM as a way to connect a printer to PC. Parallel ports are also known as LPT ports. When a PC sends data to a printer or any other device using a parallel port, it sends 8 bits of data (1 byte) at a time. These 8 bits are transmitted parallel to each other all at once. The standard parallel port is capable of sending 50 to 100 kilobytes of data per second.
The original specification for parallel ports was unidirectional, meaning that data only traveled in one direction for each pin. With the introduction of the PS/2 in 1987, IBM offered a new bi-directional parallel port design. This mode is commonly known as Standard Parallel Port (SPP) and has completely replaced the original design. Bi-directional communication allows each device to receive data as well as transmit it.
2. Serial Port
Serial ports, also called communication (COM) ports, support sequential data transmission and are bi-directional. As explained above, bi-directional communication allows each device to receive data as well as transmit it. The name "serial" comes from the fact that a serial port "serializes" data. That is, it takes a byte of data and transmits the 8 bits in the byte one at a time serially one after the other. The main advantage is that a serial port needs only one wire to transmit the 8 bits (while a parallel port needs 8 because all 8 bits are sent in one go).
The disadvantage is that it takes 8 times longer to transmit the data than it would if there were 8 wires. Serial ports lower cable costs and make cables smaller. A serial port is commonly used to connect external modems, scanners or the older computer mouse to the computer. It comes in two versions, 9-pin and 25-pin. 25-pin COM connector is the older version while the 9-pin connector is the current standard. Data travels over a serial port at 115 Kb per second. The following is a 9-pin serial port.
3. USB (Universal Serial Bus)
In the past, connecting devices to computers had been a real headache. Printers connected to parallel printer ports, and most computers only came with one. Things like Zip drives, which need a high-speed connection into the computer, would use the parallel port as well, often with limited success and not much speed.
The earlier version of Serial Port (COM Port) had 9 pins in it. Modems used the serial port, but so did some printers and a variety of odd things like Palm Pilots and digital cameras. Most computers have at most two serial ports, and they are very slow in most cases.
Devices that needed faster connections came with their own cards, which had to fit in a card slot inside the computer's case. Unfortunately, the number of card slots is limited and a Ph.D. was needed to install the software for some of the cards.
USB, introduced in 1997 is a plug and play peripheral connection, which was invented to solve all these headaches. It is used to connect various devices, for example, digital joystick, a scanner, digital speakers, digital cameras, or a PC telephone etc. to the computer. USB is generally a two-and-a half-inch long port on the back of computers or built into a hatch on the front of a computer.
The Universal Serial Bus provides a single, standardized, easy-to-use way to connect up to 127 devices to a computer. Just about every peripheral made now comes in a USB version. A sample list of USB devices that you can buy today includes,
- Printer
- Scanner
- Mic
- Joystick
- Flight yoke
- Digital camera
- WebCam
- Scientific data acquisition device
- Modem
- Speaker
- Telephone
- Video phone
- Storage device such as Zip drive
- Network connection
Connecting a USB device to a computer is as simple as finding the USB connector on the back of the machine and plugging the USB connector into it. If it is a new device, the operating system auto-detects it and asks for the driver disk. If the device has already been installed, the computer activates it and starts talking to it. USB devices can be connected and disconnected at any time.
Many USB devices come with their own built-in cable, and the cable has an "A" connection on it. If not, then the device has a socket on it that accepts a USB "B" connector.
The USB standard uses "A" and "B" connectors to avoid confusion: "A" connectors connect towards the computer while the "B" connectors connect to individual devices. By using different connectors it is impossible to ever get confused. Connect any USB cable's "B" connector into a device, and it is sure to work.
The Universal Serial Bus is the hottest product in the computer market because of the following features :
- The computer acts as the host.
- Up to 127 devices can connect to the host, either directly or by way of USB hubs.
- Individual USB cables can run as long as 5 meters; with hubs, devices can be up to 30 meters (six cables' worth) away from the host.
- With USB 2, the bus has a maximum data rate of 480 megabits per second.
- A USB cable has two wires for power (+5 volts and ground) and a twisted pair of wires to carry the data.
- On the power wires, the computer can supply up to 500 milliamps of power at 5 volts.
- Low-power devices (such as mice) can draw their power directly from the bus. High-power devices (such as printers) have their own power supplies and draw minimal power from the bus. Hubs can have their own power supplies to provide power to devices connected to the hub.
- USB devices are hot-swappable, meaning you can plug them into the bus and unplug them any time.
- Many USB devices can be put to sleep by the host computer when the computer enters a power-saving mode.
4. Firewire Port
This port was originally created by Apple and standardized in 1995 as the specification IEEE 1394 High Performance Serial Bus and is very similar to Universal Serial Bus (USB). The most important features of Firewire port are :
- Fast transfer of data - the latest version achieves speeds up to 800 Mbps. At some time in the future, that number is expected to jump to an unbelievable 3.2 Gbps.
- Ability to put lots of devices on the bus It is possible to connect up to 63 devices to a FireWire bus. Windows operating systems (98 and later) and Mac OS (8.6 and later) both support it.
- Hot-pluggable ability - they can be connected and disconnected at any time, even with the power on.
- Provision of power through the cable - FireWire allows devices to draw their power from their connection.
- Plug-and-play performance - if you connect a new FireWire device to your computer, the operating system auto-detects it and asks for the driver disc. If you've already installed the device, the computer activates it and starts talking to it.
- Low cabling cost
- Low implementation cost
- Ease of use
The key difference between FireWire and USB is that FireWire is intended for devices working with a lot more data -- things like camcorders, DVD players and digital audio equipment. Implementing FireWire costs a little more than USB, which led to the adoption of USB as the standard for connecting most peripherals that do not require a high-speed bus.
Speed aside, the big difference between FireWire and USB 2.0 is that USB 2.0 is host-based, meaning that devices must connect to a computer in order to communicate. FireWire is peer-to-peer, meaning that two FireWire cameras can talk to each other without going through a computer.
5. PS/2 Port
IBM developed the PS/2 port. It is also called a mouse port. It is used to connect a computer mouse or keyboard. A PS/2 connector is a round connector with 6 pins. Nowadays few computers have two PS/2 ports, one for keyboard and one for mouse. A colour code is used to distinguish between the two ports the keyboard port is green and the mouse has a purple port.
6. Keyboard Socket
In earlier computers the keyboard was connected using a 5-pin DIN connector with a small notch on one side. The purpose of keeping the notch was to avoid a wrong connection. With the advent of the PS/2, this socket has become obsolete.
7. Monitor Socket
This connector is used to attach a computer display monitor to a computer's video card. The connector has 15 holes.
8. Audio/Speaker and Microphone Socket
At the back of the computer system we can find three small sockets of blue, green and pink colours used to connect speakers, audio input devices and microphones to the PC respectively. The connectors for microphone and speakers look like as shown in the adjacent figure. They are colour coded to help in troubleshooting.
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