A portion of the total capacity is used to store certain functions including optimizations of the memory that support proper Nand memory operation and therefore is not available for user storage. This is disclosed on our packaging when you see the statement "Actual usable capacity may vary, and thus is not available for data storage"

PNY Continues to improve its products and will implement firmware and optimizations which may result in variance of usable capacity that is available for user storage, these implementations are required for performance and endurance of the Nand technology in PNY products.