09-10-2015, 09:41 PM
The HAL was so NT could run on differing hardware platforms, i.e. other than Intel. Specifically, this was targeted at the DEC Alpha AXP chip line - I still have an Alpha AXP/433 NT 4 box in my office somewhere - this was NT natively compiled for AXP, not an emulation. At one time DEC had a huge number of s/w engineers on the Microsoft campus at Redmond specifically engaged in doing this parallel port to simultaneously support Intel x86/AMD i586 & AXP architectures. This all ended with NT 4 - later versions did not support AXPs and DEC killed the line - they were bought by Compaq who in turn were bought by HP.
As has been mentioned, hosted VMs rely on an underlying OS e.g. IOS, Linux, Windows etc. to run normally - I/O for the VM has to be shepherded from the hardware through the host OS to the VM - this makes this sort of VM pretty slow and there are many layers that normally fast stuff like disk I/O has to go through.
Real, production, VM systems like Microsoft's Hyper-V and VMware rely on a very thin & fast "hypervisor" that virtualises the underlying hardware for each VM - in the case of Hyper-V, there is a controlling O/S, also confusingly known as a "host O/S", that is also a VM (known as the primary VM) - you can login to the primary VM and control the other VMs via a tool known as the Hyper-V Manager.
Certain chipsets have hardware virtualisation support to make the running of efficient hypervisors possible. AMD call this AMD-V and Intell call their's VT-x - interrupt handling support for VMs is also now on chipsets - AMD call theirs AVIC and Intel's is APICv.
As has been mentioned, hosted VMs rely on an underlying OS e.g. IOS, Linux, Windows etc. to run normally - I/O for the VM has to be shepherded from the hardware through the host OS to the VM - this makes this sort of VM pretty slow and there are many layers that normally fast stuff like disk I/O has to go through.
Real, production, VM systems like Microsoft's Hyper-V and VMware rely on a very thin & fast "hypervisor" that virtualises the underlying hardware for each VM - in the case of Hyper-V, there is a controlling O/S, also confusingly known as a "host O/S", that is also a VM (known as the primary VM) - you can login to the primary VM and control the other VMs via a tool known as the Hyper-V Manager.
Certain chipsets have hardware virtualisation support to make the running of efficient hypervisors possible. AMD call this AMD-V and Intell call their's VT-x - interrupt handling support for VMs is also now on chipsets - AMD call theirs AVIC and Intel's is APICv.
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