Whilst reading a VMware document on using SQL inside VMware Virtual Infrastructure i realised that i wasn’t 100% sure on what the Hard Abstraction Layer ( HAL) actually is, so i decided to do some reading up, here is my take on it.

What is the Hardware Abstraction Layer or HAL?

The HAL is a part of an Operation System that talks directly to the machine’s Hardware.

The Windows OS is able to support multiple hardware platforms without having to have different OS versions for each hardware platform thanks to the HAL. During the installation of an OS the HAL is chosen depending on the hardware platform, because of this you are normally unable to remove the HDD from one PC and move it to a PC which has different hardware.

A HAL tip when you are installing VMware VM’s using  Windows Server 2003

Windows 2003 Server unlike Server 2008 doesn’t have the ability to dynamically adjust the HAL to accommodate extra vCPU’s after installation. So if you’re creating a new VM which may possibly need to have an extra vCPU added to it in the future, it is best practice to install the OS on a VM with 2 vCPU’s as this will install the SMP (Symmetric Multiprocessor) HAL rather than the UP (Uniprocessor) HAL. Once your install of 2003 server is complete you can change your VM’s vCPU’s back down to one. You now have the option to add another vCPU whenever its needed.

*If i have misunderstood what the Hardware Abstraction Layer is, please message me direct or leave a comment.