Buttons contain the electronic circuitry to store the unique authorization for your Product. This circuitry is housed inside of a 17mm stainless steel can rugged enough to withstand being dropped, stepped on or even submersed in water. Buttons contain their own lithium power source to keep your authorization safe and secure for up to 10 years. The only reason that Holders exist is to allow Buttons to be connected to the computer. Holders have no other function and don't contain any authorization or protection information.
Holders are available for both parallel and serial ports.
There's even an Extension Holder that allows the Button to be plugged into the front of the computer. Accessing the Button is the same regardless of what type of Holder is being used. Serial port Holders cannot be daisy-chained and must be the only device plugged into that serial port. You simply provide one Button for each license of your Product. Your software can be backed up, restored or relocated as necessary, but you will always be in control of the total number of Users.