In the begining, not to sound biblical, access control manufacturers published specific card reader and carholder capacities. Life was good. Sixteen readers and 1,000 cardholders. The competition would be compelled to better these capacities and would release a system which doubled or tripled the card reader and cardholder capacities. The spec war which ensued saw these claimed capacities grow by leaps and bounds. Until a marketing genius somewhere came up with the idea of claiming "unlimited" card reader and cardholder capacity.
I have been involved in the design of card access control systems for close to 40 years. Being a very simple, old fashioned person, I established capacities of new systems by testing them under real and simulated loads and capacities. Sometimes we found that, although a system was theoretically capable of handling say, 512 card readers, with 65,000 cardholders each using their cards several times every hour with many operators all concurrently managing cardholders and running reports, performace suffered badly. We either found a way to make it perform better or we rolled back the claimed capacities.
Now, most new access control systems are claiming to support an unlimited number of card readers and an unlimited number of cardholders. I can't help but wonder how they are testing these new systems?