Saturday, January 15, 2011

System Abstraction Layer

SAL allows the portability of the operating systems—in binary format— between various platforms based on the same processor architecture. The role of this layer is to hide the specific details of the platform from the operating systems. Among the principal functions of a SAL are:

• The assumption of responsibility of initialization, test and the configuration of the hardware resources of the platform

• Providing the operating system with data structures describing the configuration

• Provision of basic services for resource management, such as choice of which processor will load (“bootstrap”) the system; basic hardware error management and error logging

• Hiding differences arising from the use of different processor architectures, or the use of different processors within a single architectural family

For IA-64 systems, Intel has introduced a further layer between the SAL and the hardware; this new PAL (Processor Abstraction Layer) layer is intended to hide the differences between the implementation details of successive generations of IA-64 processors from the SAL. For an operating system intended to be ported across processor architectures, this functionality has its natural home in a SAL.

The concept of a SAL was understood and implemented long before the term itself was introduced. As an example, the manufacturers of both proprietary and UNIX systems developed families of products which had differences in implementation—in particular, for performance reasons—and therefore often had to develop an abstraction layer to facilitate porting the OS between the various models in the range.

In the case of Windows NT, a similar abstraction layer was implemented, called HAL, for Hardware Abstraction Layer.

Source of Information : Elsevier Server Architectures 2005
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