Change VMWare vSphere Memory Usage Charts to MB or GB

There are three components you need to consider;

1. ESX Licences - ESXi (not ESX) is free but limited when free, you can't give VMs the full 8 vCPUs, don't have HA, FT or DRS functionality etc. but it works just fine with or without shared storage. If you want these functions it's going to cost.
2. vCenter - this management software costs but is the only way to make two or more ESX/i hosts work together to provide HA, FT, have DRS functionality etc. Note that the ability to live migrate guest VMs from host to host requires shared storage.
3. Shared storage - without this you can't live migrate from host to host or support HA.

So really it comes down to your downtime requirements, if you NEED HA, DRS, vMotion, FT to increase your service uptime then you need ESX licences, a vCenter licence and shared storage. If you don't need these functions you don't need any of these extra-cost items.

Oh and there are free backup solutions for unlicenced hosts, such as GhettoVCB.

There is a detailed white paper on the topic of memory management and calculations of the active memory working set size.

It basically all boils down to the fact that a guest is not using all the memory that has been assigned to it all the time. Instead, only certain ranges of memory are considered "active" at a particular time period, making the "inactive" memory a candidate for swapping, if you happen to overcommit your physical memory. You should look at the "consumed" memory if you want to roughly match it up with the memory usage within your host (deviations due to memory pages shared across several VMs may occur).