IBM created preset combinations of IRQs and I/O addresses for
serial devices. These preset combinations are called ports. The word "port" simply means a portal or two-way access. The preset combinations are called COM ports for serial devices. The purpose of a port is to make installation easier. Modems and printers, therefore, do not require IRQ or I/O settings. When assigned to an active port (as long as no other device is using that port), they will start working. The following table lists standard COM ports.
| Port |
IO Address |
IRQ Number |
| COM1 |
3F8 |
4 |
| COM2 |
2F8 |
3 |
| COM3 |
3E8 |
4 |
| COM4 |
2E8 |
3 |
