In OS/2 for SMP V2.11, all of the platform specific code has been removed from the operating system, and placed into a Platform Specific Driver. These drivers provide an abstraction layer for the underlying hardware by allowing the operating system to call generic functions to perform platform-specific operations without worrying about the actual hardware implementation. This allows OS/2 for SMP V2.11 to support new MP hardware platforms without modifying the operating system.
PSDs are 32-bit flat DLLs specified in CONFIG.SYS by using the PSD= keyword, and must conform to the 8.3 file naming convention (e.g. PSD=BELIZE.PSD). They cannot contain either drive or path information because OS/2 cannot process such information at the stage of the startup sequence when the PSD statements are processed. The root directory of the startup partition is first searched for the specified file name, followed by the \OS2 directory of the startup partition. If drive or path information is included in a PSD statement, an error is generated.
PSD parameters may be specified after the PSD's name, and may be a maximum of 1024 characters long. The parameter string is not interpreted or parsed by OS/2, but is passed verbatim as an ASCIIZ string when the PSD's Install function is invoked.
If multiple PSD statements are encountered, OS/2 will load each PSD in the order listed in CONFIG.SYS, and call the PSD's install function. The first PSD which successfully installs will be the one OS/2 uses.
PSD statements are processed before BASEDEV, IFS, and DEVICE statements.