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Comment by Youden | Hacker News Reader

Those aren't dedicated servers. They use a hypervisor [0].

[0]: https://aws.amazon.com/ec2/instance-types/a1/

Graviton is ARM-based and has offered .metal instances which don’t have a hypervisor, the latest generation being “Graviton 3” (https://aws.amazon.com/blogs/aws/join-the-preview-amazon-ec2...)

I think there's a1 (virtualized) and a1.metal (bare metal). Although I think the metal versions also include Nitro hardware.

But not my specialty.

The metal versions use the Nitro card, but run all of the virtualization on the Nitro card, so there is no hypervisor running on the machine. VMWare has had ESXi doing similar virtualization with the help of switches for a while too (although I think ESXi still has a tiny hypervisor).

Isn't there still a hypervisor present though but rather than the hypervisor running on a general purpose CPU it's running on the Nitro chipset? There's still a type 1 hypervisor involved no? How else would the hypercalls from the guests work?

There is no hypercalls. Your operating system is running directly on the CPU, same as regular bare metal servers.

There are no hypercalls and there is no hypervisor software on machines with this type of virtualization. All virtualization takes place at the network and storage device layer.

The Nitro card encapsulates packets from your machine so that they flow on the AWS network correctly, it emulates being an SSD, and it takes care of myriad other peripherals and interfaces that you might expect to have.

I think it also has a direct connection to the BMC or uses IPMI to reboot the machine when you are done with it (and another user takes it).

Ah OK, this is helpful, thanks. The IPMI functionality is certain nice to have.

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