With an m4.16xl, there's no effective difference between a dedicated or default tenancy instance - only one .16xl can run on a physical hypervisor, which is reflected in the pricing, it's $3.20/hour whether it's dedicated or not:

https://aws.amazon.com/ec2/pricing/on-demand/ https://aws.amazon.com/ec2/purchasing-options/dedicated-inst...

For smaller instances, there is around a 10% increase for dedicated, for example, for an m4.4xl, the price goes to $0.88 for dedicated tenancy versus $0.80 for default.

There is a $2/hour fee for each region in which you have dedicated instances, but that gets lost in the noise if you're using significant AWS resources. (it's $2/hour regardless of how many instances you're running)

We haven't noticed any significant difference between performance on dedicated and non-dedicated instances, and only use dedicated instances where required for compliance/regulatory reasons.

An m4.16xl has 8 physical cores; what hypervisor does AWS buy that only has 8 physical cores?

My smallest physical servers have 8 physical cores.

An m4.16xl has 32 cores / 64 threads.

okay, my error - thanks!

Why get a dedicated instance and not get reserve pricing? You can get those instances for a fraction of what you're currently paying