Port (computing)

In computing, port has several possible meanings. Which meaning is intended can usually be determined from context.

Table of contents

1 Hardware Port 2 Networking Port 3 Software Port 4 Machine or I/O Port 5 External link

Hardware Port

A hardware port is an outlet on a piece of equipment into which a plug or cable connects. For instance, a computer may have a keyboard port, into which the keyboard is connected.

Networking Port

A networking port, so named by analogy with the above, is a notational point for the connection of network programs. In TCP and UDP, multiple network services running on a single host are distinguished by port numbers; the operating system kernel uses these port numbers to sort out which packets should go to which programs. A program which is using a port, whether to await connections (i.e. to be a server) or to make connections, is said to have a socket bound to that port -- more hardware analogy. A well known port is between the range 0-1023 which were traditionally assigned by IANA. Ephemeral ports are somewhere between 1024 to 65535 depending on the implementation of the TCP/IP stack of an operating system.

List of some well known network ports:

• 20 FTP
• 21 FTP
• 22 SSH
• 23 Telnet
• 25 SMTP
• 53 DNS
• 70 Gopher
• 80 HTTP
• 107 Remote Telnet Service
• 109 POP2
• 110 POP3
• 119 NNTP
• 143 IMAP4
• 194 IRC
• 220 IMAP3
• 389 LDAP (Lightweight Directory Access Protocol)
• 443 HTTPS
• 540 UUCP (Unix to Unix copy)

Software Port

In programming, a port is a localization or translation of a piece of software to a particular API, operating system, or generally any other computing environment than that for which it was written. See porting for detail.

Machine or I/O Port

A machine port, or I/O port is a concept peculiar to Intel microprocessors. It is the primary method for microprocessor control of hardware devices. A machine port is essentially equivalent to a single-byte memory location, except that reading from it or writing to it will have an effect defined by the device in question. For example, a common use is to provide a status register, where writing to the port will determine which of up to 256 bytes will be returned by the next read operation. Unlike other architectures, Intel-based computers primarily use DMA for bulk information transfer, not control.

See also: Memory-mapped/A>

External linkList of networking ports