There are three different SRAM sizes on the different versions of the SAM3U ranging from 32 kB to 8 kB. The 4 kB embedded in the NANDFlash Controller can also be used as an SRAM, which means that the 4 kB are in addition to the embedded SRAM in the product. Lastly, there are 32 bytes that can be used as backup registers in the backup unit.