A method and apparatus for virtually expanding the rapid-access memory space of a device employing time-critical software modules and having various modes of operation. Each of the modes of operation of the device is identified. For each mode of operation, the time-critical software modules used during the mode are identified. The software modules used during all modes of operation are permanently stored in rapid-access memory. However, a software module that is used only during a particular mode of operation is loaded into the rapid-access memory unit only upon entry into the mode of operation in which it is used. The software module is loaded into a region of memory occupied by another software module not utilized during the particular mode of operation being entered.