Difference between Ardupilot Mega and Arduino Due in terms of quadcopter designing?

I have zero knowledge of this domain (designing a quadcopter).
I have Arduino Due and Ardupilot Mega. I want to design PID controller for my flight controller. What I know is Basic level coding of Arduino and
Ardupilot is open source. What I don’t know is in what terms can we differentiate arduino and ardupilot. Ardupilot is open source but the way of coding is same as arduino(i.e arduino like flexibility is offered)?

[User comment deleted]

Thanks but it made me more confuse, specifically this line. "For Ardupilot, there is support for the Cortex-M4 (STM32) and therefore, it's possible to run it on the Due."I have to use only one board. For Ardupilot Mega I have this board. And also I have seen a working Quadcopter with just ardupilot board (no other microcontroller was attached). I also have seen a lot of support for ardupilot on github. But tecnically what makes Ardupilot superior to arduino (of course Ardupilot  is specifically designed for being used as flight controller but exactly in what technical terms because I couldn't find any digestive material).

[User comment deleted]

Thanks! BTW reason for this thread was to get information on how technically they are different. I am interested in micro-controllers but since no one around me has much knowledge of this field so all I am left with is to ask forums and generous people like you.

All things considered, first we have the contrasts between an Arduino Mega and the Arduino Due. The Mega depends on the MicroChip (in the past Atmel) 8-bit ATMega2560 part. It has 256KB of program streak (8K is utilized by the bootloader) with 54 advanced I/Os and 16 simple sources of info. Likewise, there is 8KB of SRAM utilized for unstable qualities, stack, and so forth and 4KB of EEPROM for changeless capacity. It keeps running at 16 MHz.
The Arduino Due is a similar frame factor as the Mega2560. Be that as it may, the determinations are very unique. The Due depends on 32-bit ARM Cortex-M3 (AT91SAM3XBE) and works at 3.3V rather than the Mega2560's 5V. There are 54 advanced I/O pins (12 are equipped for PWM) and just 12 simple sources of info yet 2 simple yields. There is 512KB of program streak and an aggregate of 96KB of SRAM running at 84 MHz. For Ardupilot, there is bolster for the Cortex-M4 (STM32) and in this manner, it's conceivable to run it on the Due. There have been inquiries on the gathering about running it on the Due, however there have not been any genuine responses to the inquiries posted.
FWIW, the greater part of the Ardupilot stuff is focusing on bigger sheets like the BeagleBone Dark and utilizing the BBB's PRUs as the interface (Linux independent from anyone else has excessively jitter for use on PWMs without something like the PRU). The codebase has kept on becoming throughout the years and you'll need to pick and pick what you need to stack.
There is likewise the Ardupilot Super task that explicitly focuses on the Mega2560 class processor. Nonetheless, they have a unique fabricated board considered the APM2.5+ for 34.99 pounds that is the objective for this exertion. I don't know whether you can utilize a stock Mega2560. Both of these sheets will expect you to buy extras like an IMU, GPS, and so on to get something flying.
I'd check the Ardupilot and Ardupilot Super sites explicitly to perceive what you require in the method for equipment. Contingent upon what you run with, you can utilize either the Arduino IDE (Mega2560 or Due) or standard Linux advancement for something like BBB.