Xeams server can be configured to use a maximum amount of memory on your machine. By default, this value is 512MB. This means that if memory usage can never exceed 512MB. This number is referred as Total Memory.
Even though you can specify a maximum number, it does not mean Xeams will use that much memory on the machine. It will incrementally allocate small chunks of memory as needed. The sum of all these chunks is called Allocated Memory.
Used memory is the amount of memory currently in use. This number will always be less than Allocated Memory.