The PC-6601 is basicaly a PC-6001 MK2 with a built-in 3.5'' disk drive. The second optional disk drive could also be mounted. The N60m Basic od the PC-6001 MK2 has been enhanced to the N66 Basic.
The japanese adverts focused on the fact that this computer could sing with its optional speech synthesizer!
More info badly needed!
NAME
PC 6601
MANUFACTURER
NEC
TYPE
Home Computer
ORIGIN
Japan
YEAR
1985
BUILT IN LANGUAGE
N66 Basic + machine language monitor
KEYBOARD
Full-stroke keyboard, JIS standard layout, 5 function keys