A question about sram vs. sdram

Both RAM types are on the development boards so that users can design with either. Depending on the end product and implementation one is more suitable (SDRAM is cheap and less power consuming, whereas SRAM is fast and more power consuming). Usually you can get around the fact that SDRAM is slower by using a big cache size and programming your code in such a way that it will not be hindered by the SDRAM performance as much. If you look at timing diagrams for SDRAM and SRAM you'll get a pretty good idea why their performance differs.