port : Java Glossary

by Roedy Green ©1996-2008 Canadian Mind Products
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port

The word port has at least three meanings:

As a verb, it means to adapt a program to run on a different computer, SQL database, language, or Servlet womb, etc.
In the context of hardware, it refers to the channnel that data gets from the i/o devices to the RAM via the CPU. A hardware port can be a serial port for a modem to connect to, or a parallel port for a printer to connect to. It simply deals with the handshaking of sending a single character at a time to an external device.
In the context of TCP/IP, UDP or ICMP network communications it refers to a socket number to allow multiple channels to be operating independently between two computers. The Internet’s DNS/IP protocols only deal with delivering a packet to the right computer. Once arrived the packets must be assembled in order into messages and delivered to the right application. Applications are assigned numbers from 0 to 65535 called ports. Any message destined for port 80, for example, is delivered to the application handling HTTP requests. The port number can be explicitly embedded in a URL like this "www.mindprod.com:80". Port numbers above 1023 are up for grabs on any machine for your own code. Others have standard assignments. IANA maintains the list of well known port numbers.

TCP/IP UDP ICMP Ports

TCP/IP Ports
Port name	Port number
echo, used for testing.	7
DayTime, returns date/time as a string.	13
FTP, File Transfer Protocol	20 and 21
SMTP, Simple Mail Transfer Protocol	25
Time, returns 32-bit days since 1900/01/01.	37
HTTP, HyperText Transfer Protocol	80
DNS, Domain Name Service	53
POP3, Post Office Protocol version 3	110
NTP, Network Time Protocol 64 bit number with 32 bits as the integer and 32 bits as the fractional portion of seconds since 1900/01/01.	123
utime	519
timed timeserver	525
SNTP, Simple Network Time Protocol heartbeat.	580
dbAnywhere	8889

IN Windows Server 2003 you can find out which process in using which port with the Netstat -nao command.

Hardware Ports

At a hardware level are special registers called ports. When you write them you output to external i/o devices such as serial ports, parallel ports or hard disk controllers. When you you read from them, you input from i/o devices.

Serial Port Assignments
	COM1:	COM2:	COM3:	COM4:
port:	3f8	2f8	3e8	2e8
irq:	4	3	4	3

Parallel Port Assignments
	LPT1:	LPT2:	LPT3:	LPT4:	LPT5:	LPT6:	LPT7:
port:	3BC	378	278	368	268	358	258
irq:	7	5	?	?	?	?	?

IANA list of TCP/IP Port Numbers
IRQ
parallel port
ports used by various software and games
serial port
service for a list of port assignments on your own machine
UART: tool to check your serial port and IRQ assignments

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