A port can be one of three things:
- Computer hardware: A physical interface used to connect a computer to other computers or external hardware.
- Software modification: The process of modifying software to work on a new operating system or with new hardware.
- Network service identifier: A number used to identify the process to which a message should be forwarded when it arrives at a server.
The next time you go shopping for a computer, one of the features you'll want to pay attention to is the number and type of ports offered with each computer. Some of the most common types of ports include USB, Ethernet, HDMI, VGA, DisplayPort, audio jacks, and memory card slots. While these are some of the most common, there are many additional ports your existing computer may have depending on its age. Or you may need additional ports depending on your intended use of the machine and how technology changes in the future.
Ports are used to connect a computer to hardware like displays, printers, external hard drives, projectors, and more. They are also used to connect computers together, or to add a physical network connection.
To modify an application so that it works in an environment other than the one it was originally designed for, or so that it interacts with hardware it wasn't originally intended to recognize, is called porting. Porting software is rare, and it only makes sense if the cost to port is less than the cost writing a new application from scratch and if suitable software isn't already available.
Software that has been designed to be easy to port to a new environment is said to be “portable”.
Modern software that will be used on multiple operating systems is now typically developed using applications capable of outputting code that is compatible with a variety of operating systems. As a result, the needs for ports of new programs is less common than it was in the past.
Network Service Identifier
In computer networking, port numbers are used to identify the service that a specific message is associated with. When a message is received by a server, the port number is used to determine the purpose of that message. Specific port numbers are associated with specific services. Some of the most common port numbers used for Internet-enabled services include:
- Port Number 21: File Transfer Protocol (FTP)
- Port Number 25: Simple Mail Transfer Protocol (SMTP)
- Port Number 80: Hypertext Transfer Protocol (HTTP)
- Port Number 110: Post Office Protocol (POP3)
- Port Number 143: Internet Message Access Protocol (IMAP)
- Port Number 443: HTTP Secure (HTTPS)
- Port Number 465: SMTP Secure (SMTPS)
Frequently Asked Questions
How are port numbers used?
When you set up an email client to check your email, you will have to provide your credentials for the mail server where you email is stored. You may also have to specify whether POP3 or IMAP should be used to pull down your email as well as the applicable port number. When you use the email application to check your email a message will be sent to the mail server and will include the port number. The server will use the port number to determine that you are making a request for email (either POP3 or IMAP depending on the port number provided) and process the request accordingly.