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The Hardware Abstraction Layer
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| bet | 13/13 | | Sana | 21.03.2017 | | Hajmi | 0.63 Mb. | | #1024 |
The HAL is NT's interface to the raw CPU. Microsoft wanted to make NT portable across different processors. To make this portability feasible, NT's developers isolated as much CPU-specific code as possible into a separate, dynamically replaceable module, the HAL. The HAL exports a common processor model that masks the differences in various processor chips from NT. Device drivers use this common processor rather than a particular CPU type. Even different motherboards in the same processor family can differ significantly, but hardware vendors can ensure that NT will work with their boards by writing a custom HAL to work with NT.
A common difference between motherboards in the same processor family is that some are for multiprocessor systems and others are for uniprocessor systems. A multiprocessor HAL is different from a uniprocessor HAL. The multiprocessor-uniprocessor issue brings me to a little-known fact. Microsoft provides three versions of each NT release: the uniprocessor version, the multiprocessor version, and the debug version (or the checked-build version). In addition to having different HALs, uniprocessor and multiprocessor versions of NT have different ntoskrnl.exe images. The uniprocessor version of ntoskrnl.exe does not include code that is necessary for correct execution on multiprocessors. Microsoft provides the debug version of NT for device-driver developers. The debug version contains additional sanity checks and symbolic information not contained in the uniprocessor and multiprocessor versions of NT. Microsoft offers only one debug version of NT, which contains multiprocessor code and will work on multiprocessor and uniprocessor machines.
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