Zend certified PHP/Magento developer

Memory usage not adding up inside Task Manager

Task manager recognises that I have 16GB of ram actually installed in the performance tab, but inside the processes tab, looking at the percentage of memory used in total by all apps and processes and then looking at the value of memory used by each of them, it was looking like my total ram installed was less than 16GB. Doing some quick calculations, one of the games I had open was using up 1175.5MB which was equivallent to 15.6% of Memory (according to Task Manager) so if do 1175.5 * 100/15.6 we get 7535 MB of total memory. A different app was using 1560 of my memory which was equivallent to 21.6%, giving a total of 7222 total MB this time.

Anyone know why this happens?