Put another way, a ton of gravel will occupy far less space than a ton of Styrofoam.   Crushed stone, for example, has a density of 100 pounds per cubic foot (lb/ft3), which is 1600 kilograms per cubic meter (kg/m3), which is 1.6 metric tons per cubic meter.
HPSS is software that manages petabytes of data on disk and robotic tape libraries. HPSS provides highly flexible and scalable hierarchical storage management that keeps recently used data on disk and less recently used data on tape.
What is ESS? Employee self-service, or ESS, is a feature that is available with most modern HRIS. ESS allows employees to take care of many different human resources-related and job-related tasks that would otherwise need to be completed by human resources personnel or management.