One of the oldest ports that connects peripheral devices to a computer. It was intended to connect mouse, modem and other devices. But it began to be replaced by PS/2 and USB.
In a PC, there is the male (M) type of connector.
There were usually 2 ports in a computer, each with 9 pins. In older computers,
you can find ports with 25 pins (connected as COM2). To use a cable with 9 pins, you can use a reduction.
Labelling as
COM 1 and COM 2. In some cases,
COM 3 and COM 4 may be used (if you have more than 2 devices, it is a necessity). If multiple ports are needed, you can buy an extension card containing up to 8 additional COM ports. In Windows, you can find many ports from COM1 up to
COMxx. But those are just virtual ports, used by devices for communication through different buses (USB, IRDA, Bluetooth).
One-way data transfer (asynchronous transfer) with a limited throughput of 115kb/s., master/control chip UART 16550 (UniversalAsynchronous
Reciver Transceiver)
In AT computers, the connector is lead from the MB using a cable to the back part of the case. In the oldest PCs, ports were implemented through an input/output card (Input/Output). The disadvantage of using a cable is the risk of improper connection or damage. To test the port, a test connector was used, the so-called Loopback.
In ATX motherboards, the connector is fixed directly to the MB,
or is missing altogether and is replaced by PS/2 for mouse and keyboard and USB port for the other devices.
New PCs - It is suitable to move mouse to PS/2 or move the other devices to USB. USB is supposed to replace serial ports completely.
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