 There were three types of data store, Main Ferrite Store (MFS), Special Ferrite Store (SFS) and Register Ferrite Store (RFS).The MFS was used by the MCU itself to hold data for various reasons and the SFS was used for manipulating data.An example of this was that SFS2 could take the data stored in positions 1-5 and swap them with data stored in positions 6-10.