Hardware
As one of the big features of PC-6001, some IO are handled by sub CPU. IOs requiring complicated processing such as keyboard, CMT interface, etc. which traditionally don't run on main CPU would need an external hardware to control. From this perspective, the introduction of the sub CPU can be said to be very effective.
One of the special features of the PC-6001's hardware...
Also, despite there is a main memory (didn't understand this part well, doesn't make sense to me. Maybe as oppose to the sub CPU memory?), there's no spacial changes regarding to the RAM.
Regarding the main memory, there is nothing particularly unusual about the RAM (kawatta tokoro means unusual features, not changes).
Thanks to the use of Z80 (RAM) refreshing capability, controller logic is very simple.
I don't know where "thanks to" comes from but that is the basic meaning.
Edit: apparently the forum software changes Japanese characters into question marks so I changed to romanised Japanese. Oddly enough the preview showed them correctly.