scope:

The standard specifies three related, but different implementations of such cartridges, viz. Type R/W: Provides for data to be written, read and erased many times over the whole recording surface of the disk using the thermo-magnetic and magneto-optical effects. Type P-ROM: Provides for a part of the disk-surface to be embossed by stamping or other means. This part of the disk is read without recourse to the magneto-optical effect. All parts which are not embossed provide for data to meet the requirements of Type R/W. Type O-ROM: Provides for the whole of the disk surface to be embossed and reproduced by stamping or other means. This type of disk is read without recourse to the magneto-optical effect.