The actual amount of available memory with IDPrime MD cards (830 or 3810) is around 45K bytes. The value given by the MiniDriver Manager for an MD card has to be considered as an indication only. With a regular .NET card, a specific command of the OS allows to return the effective available memory, matching the value displayed by the MDM. But there is no corresponding function with the java card, so we consider that there is "at least" 32K of free memory (45K in fact). When creating or removing files in the card the value is updated accordingly. But it concerns only the file system, the keys are not taken into account for the calculation. As a conclusion, you will be able to load up to 15 certificates in the MD cards, as it is specified for this product. Concerning the .NET, it is recommend to keep at least 25KB of free memory to get the best performance from your smartcard.