$ banks are YBOS banks whose names begin with "$". Any banks named this way are treated as special banks by both YBOS and ANALYSIS_CONTROL. ANALYSIS_CONTROL does not delete $ banks between event reads, they stay in memory for the duration of the job. In this way they can be used to store information that is constant throughout the job. For example users may wish to store parameters given in a talk to entry in a $ bank such that the number of the bank is equal to the parameter set number. In this way the event entry of the same module may inquire from A_C which parameter set the user wanted the module run with, directly locate the corresponding YBOS bank, and use the values stored there for making the appropriate cuts or running the appropriate code. Another use is to accumulate statistics for a job in a $ bank and then output the information to a data base or a log file at the end of run or end of job. It is strongly suggested that you LIMIT the USE of $ BANKS AS OUTPUT BANKS. ANALYSIS_CONTROL will not write $ Banks on event records they can exist only on BEGIN, END, and OTHER type records. If you must have them it is suggested you copy them to a new name just before you exit your module. The only reason to write a bank to an output file is if the next process in the analysis chain is going to read and use the information. However because of the way YBOS treats $ banks the above two applications are at odds. If the $ bank is used to hold talk to parameter set values then the correct thing for YBOS to do if it has a $ banks already in memory and one with the same name on a file, is to ignore the on in the file. This is the default in this situation. In the second application you wish to read in some history information about the previous job, so you would need the $ bank from the file. To do this you would use the "INPUT OVERWRITE$" command. However you can not run in both modes in the same job. So if you have a job that uses $ banks for both purposes there is no solution. This is why it is better to rename them before you output them.