As with all MELDAS 500-series controls, LH and RH cassettes are both flash ROM's. LH cassette contains the system software (interpolation algorithms, G-code compiler, etc). During a software update, the data can be re-written. However, this is rarely done and usually not necessary. The RH cassette contains user PLC program in ladder and/or C-language as well as possibly some macros created by the machine builder. This data can also be overwritten with special knowledge and equipment. Normally, only the machine builder would be doing this.
User programs, tool data, all parameters (system, machine, user) all reside in the S-RAM (QX-424 on the CPU board) and are backed up by battery. The machine parameters and system parameters are automatically backed up to the EEPROM on the CPU board every time you power off. Canned Cycles reside in the S-RAM also, but a master copy of these is included in the system software. If you get a flat battery and lose the S-RAM memory contents, you can reload the canned cycles from the LH cassette whilst the machine and system parameters will automatically restore themselves from EEPROM. The NC type and serial number are also stored on the EEPROM (which is a removable chip on the CPU board).
Regarding memory used for dripfeeding, I would guess that this is a function of the D-RAM (dynamic RAM) which also resides on the CPU board. This is like "RAM" found in a standard PC which means it only stores data whilst NC power is on.
Hope this helps.