This application note describes how to develop a USB Mass Storage application using an ST7265x microcontroller. The proposed solution includes a generic USB Mass Storage Layer (MSL) compliant with the USB Mass Storage Class that can be used for all types of storage media (FLASH memory cards, hard disk drive, etc.) and a dedicated Media Access Layer (MAL) add-in for each type of storage media. The MSL and the MAL modules are available to ST customers on request. Contact your ST sales office to obtain the ST7265 Mass Storage software. The MSL and the MAL must be considered as function libraries and therefore cannot be modified by the user. The software interfaces of these function libraries provide the user with the required flexibility for designing his application: – type and number of media, – insertion/withdrawal management, – protection management, – user interface. Note that the MAL requires the use of certain fixed MCU pins to interface with the various mediums. As a result, a specific application hardware configuration is required when using the MAL.