Other software may report differently as explained below. Many BIOS routines only check for two serial ports and three parallel ports. As PCs became more popular, the need for more ports grew. However, DOS will only recognize a logical port whose physical address has been placed in the RAM table. Many application programs do not use DOS to interface to ports, so that it may not be necessary to include a port's address in the system tables.
Considerable confusion exists regarding proper logical and physical port address.
Strictly speaking, there is no proper physical address for any of the logical ports. The logical port structure permits any physical address to be placed into its tables. When this is the case, the logical port addresses are not always used properly. Other programs do not use logical addresses at all, and just refer to physical addresses. Still others convert logical to physical addresses using their own table.