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Appendix E. The Hardware Abstraction Layer (HAL)

The Hardware Abstraction Layer is a software interface between the hardware and the rest of the operating system that makes Windows NT portable across platforms. The HAL also acts as the interface between the operating system and the controlling hardware of symmetric multiprocessing processor machines (SMP).

Windows NT Server 4.0 is shipped with a HAL for both the single or multiprocessor platforms available from Intel, MIPS, PowerPC and Alpha. The HAL for each platform is different; even the HAL for variants of the same platform could differ drastically. However, the virtualized processor presented by each HAL to the microkernel is identical.

Depending on the design of the platform, the addition of more processors in an SMP environment could improve the performance of the server substantially.

On a machine with only one processor installed, Windows NT will, by default, try to install the single processor version of a HAL. This is the case even when the machine is multi-processor capable. If you accept the default of a

single-processor HAL and later wish to add a second processor, you will need to upgrade your system. This may be a difficult task.

There are two methods to achieve this:

1.Upgrade the HAL

2.Reinstall Windows NT

These are described in the following sections.

Note

If you have a server that is multi-processor capable, we recommend that you initially install a multiprocessor HAL. This will save you time and effort later when and if you decide to upgrade to a multiprocessor environment.

E.1 Upgrading the HAL for Multiprocessor Use

The method described in this section makes use of the UPTOMP.EXE utility that is available from Microsoft in the Microsoft Windows NT Server Resource Kit (ISBN: 1-57231-344-7). When you want to upgrade a single processor computer with Windows NT 4.0 installed to a multiprocessor system, several files have to be changed.