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Com ports

Discussion in 'Tech Talk' started by echo99, Dec 1, 2004.

  1. echo99


    Apr 15, 2004
    What is a com port is this hardware or software? Is there only 4 or is there 256 of them?
  2. 0100010

    0100010 Millennium Member

    Sep 15, 1999
    Com ports are software. Depending on your OS, you can have up to 4 (Win 9x), or up to 255 of them (WinXP).

    On older systems, com ports are pre-assigned in BIOS to hardware on the motherboard such as serial (DB9) and on some systems IR interfaces. Com ports also take up their own IRQs in the IRQ default assigment list; Coms 1 and 3 share and IRQ and Coms 2 and 4 share an IRQ - it is through IRQ sharing that XP can create up to 255 com ports.

  3. rbielak

    rbielak PPD

    Jul 17, 2003
    Right behind you
    Sorta-kinda-sorta right.

    Technically, a COMM port (COM or communications port) is a piece of hardware, firmware and a piece of software -- on Intel computers, it's usually represented by a DB9 or DB25 shell, an PROM or EPROM chip (controller chip) and the actual software used to configure it (your OS or BIOS. Sometimes, there is no DB shell (a place to plug something in), such as in cases like an internal modem or other device that communicates externally by another means (e.g., a RJ-11 phone jack) and internally, it commuicates via the data bus to the CPU.

    You use software (The BIOS, the operating system, etc.) to configure the COMM port so that you know where to set your software application (e.g., a terminal program, a dial-up software package, a fax software program) to point to in order to use that particular COMM port.

    On older computers, the COMM port was configured in the BIOS (Basic Input Output System), which is contained in non-volatile RAM (Random Access Memory), or NVRAM. Typically, one configured a port for a specific I/O address range (input/output), such as 03F8-03FF or 02E8-02EF, and a particular IRQ (interrupt request - used to signal to the CPU when it's "finished" processing something).

    With today's software and operating systems, the OS handles all the I/O addressing and IRQ settings - you just "Plug-N-Play" ... :)

    No, not Glock related, but ... :)
  4. SamBuca


    Aug 9, 2002
    Carlisle, PA
    Oh boy ;Q

    In layman's terms, it's's the plug on the outside of the machine and it's something in the software.

    It's your serial port and there is usually one connected.
  5. rbielak

    rbielak PPD

    Jul 17, 2003
    Right behind you
    Not necessarily. You can have a computer WITHOUT an "outside plug" (as you call it, assuming you're referring to a DB9 or DB25 shell) - and when you add an internal modem, for example, it has hardware and firmware that is accessed (by software and/or OS) as a typical COM port, but you don't have to have an "OUTSIDE plug" in order to have a COM port.

    Again, not completely accurate. Technically, yes, a serial port is a type of COM (communications) port, but not all COM (communications) ports are serial ports.

    Not worth debating it any further, unless our Glock pistols come equipped with one, that's for sure ... :)