WinCE ROM vs RAM

In a Microsoft? Windows CE .NET–based system, the ROM stores the entire operating system, as well as the applications that come with the system. If a module is not compressed, ROM-based modules are executed in place. If the ROM-based module is compressed, it is decompressed and then paged into RAM. All read/write data is loaded into RAM. The option to enable compression in ROM is controlled by the OEM. Executing programs directly from ROM saves program RAM and reduces the time needed to start an application because the program does not have to be copied into RAM before it is launched. Programs that are not in ROM but are contained in the object store or on a flash-memory storage card are not executed in place; they are paged into the RAM and then executed. Depending on the OEM and the driver options on a specific Windows CE–based platform, the program module can be paged on-demand. One page can be brought in at a time or the entire module can be loaded into ROM at once.

The RAM on a Windows CE device is divided into two areas: the object store and the program memory. The object store resembles a permanent, virtual RAM disk. Data in the object store is retained when the system is suspended or soft-reset, and devices typically have a backup power supply for the RAM, to preserve data if the main power supply is interrupted temporarily. When operation is resumed, the system looks for a previously created object store in RAM and uses it if one is found. Devices that do not have battery-backed RAM can use the hive-based registry to preserve data across boots.