The architecture will see its first realization in the Itanium -- formerly Merced -- and McKinley microprocessors.

The Intel documents provide some interesting hints at new tacks that Intel is taking as it embraces the 64-bit world. One of the seldom-discussed, but most interesting, technical areas is the interface between the processor and the firmware.

Traditionally, firmware has been called BIOS, which stands for Basic Input/Output System. It's a term taken from the early days of the PC, and it's currently used to refer to the low-level software used to get a system started and to interface the basic hardware with the chip's control software.

Firmware in the IA-64 architecture has grown greatly in complexity. From relatively well-contained modules in Intel's 32-bit architectures, IA-64 firmware has become a three-tentacled technical beast that connects the basic Itanium or McKinley microprocessor to Windows or Unix-like operating systems.

The three IA-64 firmware layers comprise the processor abstraction layer (PAL), system abstraction layer (SAL) and extensible firmware interface (EFI).

Intel's lone PAL

The PAL has been developed by Intel and will be delivered along with the Itanium to IA-64 OEMs who plan to build systems around that chip. However, those OEMs are expected to provide the SAL and EFI firmware themselves.

According to an Intel technical document, "The PAL layer is developed by Intel and delivered with the processor." The SAL and EFI firmware are developed by the platform manufacturer and provide a means of supporting value-added platform features from different vendors.

That's a double-edged sword, at least one expert familiar with the situation said. On the one hand, OEMs building IA-64-based systems must grapple with writing two of three layers of new boot code. On the plus side, that gives them the opportunity to differentiate their systems -- something they're going to have to do if they're going to stand out in a field crowded with Itanium- and McKinley-based servers. It's known that Hewlett-Packard Co. and IBM Corp., among others, are working hard to differentiate their IA-64 offerings. HP has already alluded to work that would encompass proprietary boot code.

In general, IA-64 processors such as the Itanium boot at a different location than IA-32 Pentium-family chips. That necessitates some mild gymnastics in those cases in which the Itanium runs legacy IA-32 code. All the IA-64 chips are supposed to run 32-bit Pentium software without the need for advance recompilation or porting of any sort.

According to Intel's technical documents, IA-64 chips execute PAL firmware to test and initialize the system and then continue execution in the IA-64 instruction set to boot the system -- something that obviously can't be done on a Pentium. However, the next layer of firmware, SAL, can switch to the IA-32 instruction set if needed to run IA-32 BIOS code.