1\section{Other OSes} 2 3Most Unix-derived Operating Systems (Linux, BSD flavours, OpenSolaris, etc) 4integrate their \ac{ahci} subsystem into a larger disk subsystem with support 5for IDE disks, \ac{sata} disks (via \ac{ahci}), CDROM/DVD drives, and also 6floppy drives. 7 8This larger disk subsystem often utilizes a general buffer layer which the OS 9kernel provides to its subsystems. Furthermore most Unix derivates -- due to 10their essentially monolithic nature -- couple the different layers of their 11disk subsystems (transport layer, message format and disk commands, e.g. 12\ac{ahci}, \ac{sata} and \ac{ata} respectively) using function pointers and 13most of them have in-kernel structures that describe commands that are issued 14to the disk in a message format and transport agnostic way. This makes those 15systems relatively easy to extend by adding a new layer implementations (e.g. 16when \ac{ahci} was first implemented a few years ago, it was as simple as 17providing a new transport layer implementation for disks attached to \ac{ahci} 18controller). 19 20\subsection{FreeBSD} 21 22FreeBSD employs the \ac{cam}\footnote{FreeBSD \acs{scsi} Documentation can be 23found under 24\url{http://www.freebsd.org/doc/en_US.ISO8859-1/books/arch-handbook/scsi-general.html}} 25framework to seperate implementation of the driver for the I/O bus from the 26device driver for the attached device. Therefore, FreeBSD's \ac{ahci} driver is 27realized as a \ac{sim} handling the I/O operations needed to get an \ac{ata} or 28\acs{scsi} command to the device (transparently using the packet interface of 29\ac{atapi}). Other aspects of the storage system, such as filesystem or disk 30driver do not have to be modified. 31 32\subsection{Linux} 33 34Linux handles access to \ac{ata} devices with libATA\footnote{The libATA 35Developer's Guide can be found under 36\url{http://www.kernel.org/doc/htmldocs/libata.html}} which unifies interfacing 37with \acs{scsi} and \ac{ata} based devices and adapters in a common API. libATA 38can translate \acs{scsi} commands to \ac{ata} and vice-versa or simulate a 39certain command if there is no translation possible. Drivers for adapters only 40need to implement hooks for basic device operations and communication. 41