ATiny102/104 supports both external programming and internal programming (self-programming). Whereas, the ATtiny4/5/9/10 does not support internal programming (self-programming).
The ATtiny102/104 provides a Self-Programming mechanism where a bootloader can be used to program an application code into the internal flash. Flash Self-programming is supported for the full supply voltage range (1.8 – 5.5V).
The flash in ATtiny104/102 does not support Read-While-Write, and cannot be read during an erase or write operation. Therefore, the CPU will halt during the execution of a write or erase operation. Only WORD_WRITE and PAGE_ERASE commands are supported in self-programming. The CPU can execute Page Erase and Word Write in the NVM code memory section to perform programming operations.