For Compact Discs(CD) and Digital Versatile Discs( DVD), the Lead- In is the preamble located at the beginning of the data recording after the Program Calibration Area ( PCA) and Program Memory Area( PMA) data fields.
The Lead-In contains the Table of Content ( TOC) of the respective session. The Lead-In area can contain up to 4,500 sectors and thus be up to 10.5 megabytes( MB) in size. For compact discs that are still being written to, the lead-in provides the address range for the recordable sectors.
The lead-in area is located at the inner radius of the recording and is therefore also referred to as the Inner Guard Area (IGA).