目前，计算机主板IDE控制器连接的硬盘有ATA（AT Attachment）类型和ATAPI（AT Attachment Packet Interface）类型。那么，软件程序BIOS或者Linux内核是如何才能识别出硬盘是那种类型的呢？

在参考文档[1]中，定义了识别硬盘类型的方法，如下所示：

A device not implementing the PACKET command feature set shall place the signature in the Command Block registers listed below for power-on reset, hardware reset, software reset, and the EXECUTE DEVICE DIAGNOSTIC command.

If the device does not implement the PACKET command feature set, the signature shall be:

Sector Count 01h

LBA Low               01h

LBA Mid               00h

LBA High              00h

Device                  00h

A device implementing the PACKET command feature set shall place the signature in the Command Block registers listed below for power-on reset, hardware reset, software reset, the EXECUTE DEVICE DIAGNOSTIC command, and the DEVICE RESET command.

If the device implements the PACKET command feature set, the signature shall be:

Sector Count 01h

LBA Low               01h

LBA Mid               14h

LBA High              EBh

Device                  000x0000b where x equals 0 except when responding to a

DEVICE RESET, IDENTIFY DEVICE, or READ SECTOR(S)

command. For a DEVICE RESET, IDENTIFY DEVICE, or

READ SECTOR(S) command the value of x is not changed

from that existing when the command is written to the

Command register.

在经过软件复位或者硬件复位等操作后，比较LBA Mid和LBA High寄存器中的值是否分别是14h和EBh，就可知连接的硬盘是ATA（AT Attachment）类型还是ATAPI（AT Attachment Packet Interface）类型。

参考文档：

[1]. Information Technology – AT Attachment with Packet Interface – 6(ATA /ATAPI-6)