Privileged architecture library. PAL is part of the Alpha architecture. It is a software mechanism for performing low-level operations such as interrupt handling, TLB management, and atomic operations that were implemented on VAX as microcode. On Itanium systems, the same functionality is provided as part of the operating system. Whenever possible, the BLISS, C, and Macro compilers for OpenVMS I64 convert CALL_PAL macros to the equivalent operating system calls for backward compatibility. Not all Alpha PAL operations are implemented on I64; in some cases, programs that call PALcode directly might need to change.
Processor abstraction layer. Part of the Itanium architecture that is implemented in firmware. Provides a consistent interface for processor-specific functions such as hardware errors or system initialization. Generally speaking, SAL isolates the operating system from platform-specific implementation differences, while PAL isolates the operating system (and SAL) from processor-specific differences.