ROM is Read Only Memory. You can't write bits and bobs of data to it, it's read-only. It's used for the operating system. If it's Flash ROM it can be updated, but it has to update the whole area of memory, not just a little bit of it. Flash ROM has only a certain limited amount of times it can be 'flashed' (may it be a thousand or so times). Useful enough for flashing entire operating systems or whole banks of sounds, but not for flashing individual patches all the time.
RAM is Random Access Memory. This type of memory is volatile - in other words it's temporary. As soon as you switch off the synth, everything held in RAM is lost. However if there's a backup battery then this helps retain the data in the memory until you switch the synth on again.
Think I mis-read the question, sorry. I know on my old Indigo you can flash one of the ROM banks with new patches en-masse if you wanted. But you only have individual patch edit capability on the first two (RAM) banks, and this data is held in place by the
backup battery (shown on the bottom left of the blue dashed Mainboard box - it's a standard flat, round CR2032 battery - the size of a coin). You can't edit individual patches on the ROM banks - you have to flash them instead. Maybe they don't allow more RAM banks as it would drain too much current from the battery? I'm unsure as to this.
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PS > And another thing! Will the Ti|3 have user customisable/importable wavetables?

A ribbon-controller or XY-Pad might be nice, too, please! Thanks!