Dynamics Ax Systemclass for RECID

As you all know that Dynamics Ax uses recid(Record Id)to uniquelly identify a record in the database. 
Advantage of RecId 
1.By default system uses Recid as primary index,so if query optimizer didn't find any index to use then it will use RecId.

Dyamics Ax uses SystemSequence class(AOT->SystemDocumentation->Classes) to generate recId for table.
Using SystemSequence class you can reserve RECID's for your table.
Ax Kernel uses SystemSequences Table to generate the Recid for table as shown below
Goto AOT->SystemDocumentation->Tables->SystemSequences ,