Can anyone explain what is Windows HAL and what is it used for?

Question

Cheers...

I understand that it stands for Hardware Abstraction Layer but what exactly does it do ? Is it designed for high level languages like VB to communicate with the hardware ? What about the IN/OUT instructions do these instructions call into a HAL routine or do they communicate directly with the hardware's device driver via the I/O manager ?

Thanks in advance

Answer 1

I understand that it stands for Hardware Abstraction Layer but what exactly does it do ?

It's essentially the "non-portable" part of the NT kernel, provided as a seperate module so that NT could be ported to multiple processor architectures. Example: interrupt routing.

Is it designed for high level languages like VB to communicate with the hardware ?

No. It is meant as support routines for the NT kernel. If you are coding in user mode (as you would be as in high level languages like VB) you have no need to know it exists.

What about the IN/OUT instructions do these instructions call into a HAL routine or do they communicate directly with the hardware's device driver via the I/O manager ?

When you use the the in and out instructions, this is talking directly to the CPU. This is entirely unrelated to the NT kernel topics you are discussing. There is no HAL there. There is no NT I/O manager. These instructions are what the x86 instruction set provides for talking to devices through an I/O address.

Answer 2

The HAL is designed to 'abstract' details of the hardware away from the operating system (It is a kernel component).

It provides routines to kernel for dealing with machine specific instructions (afaik includes handling of things like AVX state preservation through a context switch) as well as other details such as interrupts (Google 'Interrupts IDT' (no quotes))

Note that the HAL does not fully sit below the kernel, as the kernel still talks directly to hardware in some places, however the HAL also depends on the kernel for many of its functions (as such they often come in matched 'sets')

http://support.microsoft.com/kb/99588

Answer 3

The HAL is like an isolation layer, it means that things on either side of the layer can change, and (theoretically) it will have no effect on the other side.

This means various different kinds of hardware can be below the HAL, and the software that calls through the HAL doesn't care.