What is the difference between read only and read-write RFID Tags?

Read-Only Tags have a unique serial number associated with them i.e they just have this serial number stored in the RFID Tag IC. This serial number is added to the tag at the time of manufacturing and cannot be updated or modified. These tags do not have any additional memory. They are widely used in applications that required simple identification like clothing stores and other applications which just require the tag to identify a product.

Read-Write Tags on the other give users the ability to update or re-write the information stored on the tag. The serial number of the tag can be updated as required, readers can also write information on to the tag when required, providing some sort of read log. These tags usually have EEPROM memory which can be updated as and when required. Once this memory is updated, Read-Write Tags have an option to be locked which prevents overwriting of data or tag tampering. These tags are significantly more expensive than Read-Only tags, however, have a number of use cases which can justify the higher price.

Another type of tag that is in-between Read-Only and Read-Write tags is the Write Once, Read Many (WORM) Tags - These tags can be encoded by the user one time, after this the tags gets locked and the information stored can't be altered. This tends to be more secure than Read-Write tags.