Shares, reservation, and limit are settings used to allocate and manage memory resources for VM:

• Shares: Specifes the priority of a VM to get resources during a period of contention. When resources in a ESXi host are limited and the VMs compete to access resources, the VMs configured with higher shares will have higher priority to access more of the host's resources. Shares can be specified as High, Normal, or Low with a ratio of 4:2:1 and should be used for resource pools or sibling VMs (sibling VMs have the same parent in the resource pool hierarchy).
• Reservation: Specifies the minimum allocation guaranteed to a VM. When the VM is powered on, the server assigns resources based on the specified minimum reservation regardless of whether the physical server is heavily loaded. Resources are allocated only when requested by the VM and if the host's unallocated resources don't meet the reservation requirements, the VM cannot be powered on. Default reservation is set to 0.
• Limit: Specifies the maximum amount of resources a virtual machine can use. If the limit is not set, a VM cannot consume more resources than what is configured in its setup; if a VM is configured with 2 GB of RAM, it will be limited to consume no more than 2 GB. The default limit value is set to Unlimited.

To configure shares, reservation, and limit parameters, proceed as follows:

1. Right-click the VM to configure and select Edit Settings
2. Access the Virtual Hardware tab and expand the Memory item
3. Set the appropriate values then click OK to confirm: