now to fig7 and 8 there are illustrated alternative formats for data buffered in front end volume 39 or stored in alternate volume 43 referring first to fig7 the identity of the secondary volume to which the data is to be written is indicated in a volume column 121 the address of the data to be written in the secondary volume is indicated in an address column 123 the data to be written is in a data column 125 the data records are stored in the various lines of the table of fig7 in order to transfer data from the front end volume to a secondary volume 121 a record is selected from the table of fig7 and the data in column 125 is written at the address specified in column 123 for example in line 127 of fig7 data is written at address location 0002 of volume number 112 after copying the data record the data record is removed from the front end volume if a new record is received at the front end volume and there is another record with the same volume id and address the data of the new record is overwritten on the previous record referring now to fig8 there is illustrated an alternative data format for the data in the front end volume or the alternate volume the table of fig8 includes.