0x3F6

0x3F6 is a hexadecimal I/O port address used in the architecture of IBM PC compatibles. In decimal terms, it equals 1014. On traditional x86 systems it is associated with the primary IDE (ATA) controller and serves as the Alternate Status Register (read) and the Device Control Register (write).

The Alternate Status Register at 0x3F6 provides status information about the IDE controller without using the main status port (0x1F7). The Device Control Register, accessed by writing to 0x3F6, controls low-level controller behavior, most notably enabling or disabling interrupts and issuing a soft reset to the controller. These functions are used by low-level drivers and BIOS routines when issuing commands to hard drives or optical drives connected to the primary IDE channel.

In modern systems, legacy I/O ports for IDE are often preserved for compatibility or emulated in virtualization, but may be deprecated or inaccessible on newer hardware. The IDE interface on the primary channel also uses other ports in the range starting at 0x1F0 for data and command registers, with 0x3F6 playing a specialized role for status polling and device control. For the secondary IDE channel, corresponding ports exist at 0x170–0x177 and 0x376, with 0x376 typically serving as the secondary channel’s device control/alternate status port.

Summary: 0x3F6 is a key legacy I/O port in PC hardware, primarily tied to the primary IDE controller’s alternate status and device control functions, enabling status reading and interrupt control during low-level drive operations.