internal flash ( i can use it with other devices using another pins as SS ) and another one on pins 12,13,14,15.
Honestly I don't know enough about it. I did think that a SD card in 4 bit mode might work (what I was interested in) but the information I read about it eliminated that possibility. https://github.com/esp8266/Arduino/issues/4298
Do some searches on HSPI and see what you find.