so i am using arduino as ISP . i was doing this with atmega644 just fine but now i replaced it with atmega1284 the thing is , it says there is no such device ?? and i cant find it in the list of devices in AVRdude
I don't know the answer but I suspect if you change your title to "Can't upload sketch to Atmega 1284" you might attract help more quickly. If you modify your Original Post you can change the title.
I thought it was down the back of the sofa