Data model. Under a data model we understand correlations between sizes of types accepted within the framework of the development environment. For one operations system there can exist several development means adhering to different data models. But usually only one model prevails - the one corresponding to the hardware and software environment most. An example is the 64-bit Windows operations system in which LLP64 is the original data model. But for compatibility purposes the 64-bit Windows operations system supports execution of 32-bit programs which work in the mode of ILP32LL data model.