Hello Sandeep,
This keyword serves as input for the MemoryBanker. This is a tool that automatically determines an optimized memory layout for your application. If you do not use MemoryBanker you should simply ignore the keyword since it has no effect whatsoever. As far as I remember there is a MemoryBanker chapter in the linker manual with more information. However, please note that this tool is intended more for users who are not familiar with the S12X memory architecture (its goal is to optimize the memory layout starting from the large memory model). If you are using the banked or small mem. model, this is probably less useful for you.
