I would like to know whether the DB-25 port is a serial or parallel port. These ports are otherwise known as printer ports, aka LPT port.

I'm very confused about this since, according to Wikipedia, this port is considered part of the D-Subminiature connectors, which are mostly used for RS-232 serial communication.

On the other hand, we know that this port is known as the parallel printer port. So, why all this confusion? Is this confusion only associated with DB-25 ports on computers? Then how about other devices that have DB-25 connectors (mostly male DB-25)?

  • 1
    Your question is not clear. It sounds like you already know that DB-25 is a parallel connection. You can determine if the connector is serial or parallel by looking at how many pins there are. – Ramhound Feb 6 '13 at 13:40
  • Apart from me knowing or not, what is YOUR opinion?? – Sam Feb 6 '13 at 13:45
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    Post a picture of the connector and/or tell us how many pins there are. My opinion is worthless. My answer based on facts isn't worthless. – Ramhound Feb 6 '13 at 13:47

Is DB-25 port Serial or Parallel?

A DB-25 connector could be serial port or parallel port or something else.
A DB-25 connector is a generic connector.
It is not exclusively used by just one interface (like HDMI or USB connectors are).

On a modern PC, a DB-25 (especially a female connector) is typically associated with a parallel (aka LPT) port.
On older computer and telecommunication equipment, a DB-25 connector is typically a RS-232 serial port.

Prior to the mid-1980s, RS-232 ports typically used DB-25 connectors.
Printers used RS-232 interfaces and/or custom interfaces.
One of those interfaces, a parallel interface using a 36-pin connector developed by Centronics, became an industrial and then an IEEE standard.

When IBM introduced its PC, it substituted the large Centronics connector with a slimmer female DB-25 for the LPT port. The female DB-25 connector was typically used for DCE RS-232 ports (e.g. a phone modem), and this was a new application for that connector. The RS-232 port(s) on the IBM PC used male DB-25 connector(s).

When IBM introduced its second-generation PC/AT, in 1984, IIRC it substituted the large male DB-25 connectors for RS-232 ports with "DB-9" (actually a DE9) connectors that today's users associate with "serial" ports. The parallel LPT port continued to use the female DB-25 connector.

  • Awesome! That's exactly what I was looking for! Thanks! – Sam Feb 13 '13 at 11:55

The connectors themself arn't actually specific to a protocol - It simply refers to the number of pins and that its sub miniature. You could in theory wire up any suitable connector to the right electrical connections and to use it.

In most systems I've seen, serial ports had 9 pins (since they didn't implement the whole 25 pin standard). I could also have, in theory the same 9 pins on a mini DIN connector or used the same 9 or 25 pins for another protocol.

On the other hand, printers often had a centronics port rather than a DB25, and once again, the physical connector simply had to support the minimum amount of pins the electrical standard needed.

At the end of the day the smart thing is to check before you plug anything in ;p

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