Hyper-V Resource Control
Virtual Machine Reserve (percentage) – this value says how much CPU is kept aside for the running Virtual Machine.
Percent of total system resources – this is a precent of a Virtual Machine processor time, that is measured by how many processors are assigned to the virtual machine
Virtual Machine Limit (percentage) – this is a percent of CPU that the running Virtual Machine is not allowed to go over the top of
Percent of total system resources – this is percent of a VM processor time, that is measured by how many processors are assigned to the physical computer
Relative Weight – this is used to decide how CPU is distributed. (Basically a virtual machine with the higher weight (say 500) will get twice the CPU time as a virtual machine with a weight lower weight (say 400).
Basically on a 1 CPU and 4 Core computer you can run 40 1 CPU Virtual Machines if their reserve is 10%.
Source: MS TechNet Forums.