as pages 2 5 now the page numbers merely define a local page sequence and should not be confused with the page lsn 39 s the latter are pointers embedded in each page when written through to dasd storage after being logged which denote the position of the redo undo records in the log containing the most recent page modification initially the page lsn 39 s are set to 0 likewise the icb 39 s in the smp for all the d pages are set to 0 as is the icbu lsn in the header page lastly since no backup exists for file a there is no entry in the system catalog as seen in fig3 the system catalog broadly contains a location pointer and other archive or backup copy information for an either a full or incremental copy of file a and other files typically such archive copies would be stored on an auxiliary store such as an automated tape library any recovery use of the backup copy would require access of the tape library and staging therefrom to dasd storage referring now to fig4 there is shown the state of file a and the system catalog after a full copy fc has been taken of file a subsequent to initial loading and prior to any modifications being permitted to the data.