user31105: Today I got my clone Arduino and connected it to my real Arduino and they both work. (UPDATE: The Arduino noted as real Arduino probably also is not a real Arduino; however both work fine).
However, I see some differences and wonder if these are good or bad:

My questions
1) At number 1 there is on the clone arduino a 12 MHz oscillator? What does it do? And since there is also the regular 16 MHz oscillator I wonder why there are two.
2) At number 2 are 4 holes without any explanation. What is the function?
3) At 3 there are 12 holes (sorry that only 9 are visible, under the blue/black cable are 4 more holes with silver square around them. 
4) At 4 there is a SCL and SDA which are used for SPI I think, but these are not on the original Arduino. But the original Arduino has 6 pins at the same location and 4 holes (where 2 of them are marked as JP2).

user13432: The best help is the schematics for the clone. 


1) At number 1 there is on the clone arduino a 12 MHz oscillator? What does it do? And since there is also the regular 16 MHz oscillator I wonder why there are two.

Lower left on the schematics is the 12 MHz crystal. It is for the CH340G (USB-UART chip).

2) At number 2 are 4 holes without any explanation. What is the function?

Lower middle is the pins X1. They are extra signals from the USB-UART chip (CTS, DSR, R and DCD).

3) At 3 there are 12 holes (sorry that only 9 are visible, under the blue/black cable are 4 more holes with silver square around them.

Upper right on the schematics are the extra pins. This might be handy. 

4) At 4 there is a SCL and SDA which are used for SPI I think, but these are not on the original Arduino. But the original Arduino has 6 pins at the same location and 4 holes (where 2 of them are marked as JP2).

The original has an extra ISP pins (ICSP1) for the ATmega16U2. See the schematics. The clone has the new layout I2C signals extending beyond pin 13.

31105: <p>Today I got my clone Arduino and connected it to my real Arduino and they both work. (UPDATE: The Arduino noted as real Arduino probably also is not a real Arduino; however both work fine).</p>

<p>However, I see some differences and wonder if these are good or bad:</p>

<p><a href="https://i.stack.imgur.com/Z9edm.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Z9edm.jpg" alt="enter image description here"></a></p>

<p>My questions</p>

<p>1) At number 1 there is on the clone arduino a 12 MHz oscillator? What does it do? And since there is also the regular 16 MHz oscillator I wonder why there are two.</p>

<p>2) At number 2 are 4 holes without any explanation. What is the function?</p>

<p>3) At 3 there are 12 holes (sorry that only 9 are visible, under the blue/black cable are 4 more holes with silver square around them. </p>

<p>4) At 4 there is a SCL and SDA which are used for SPI I think, but these are not on the original Arduino. But the original Arduino has 6 pins at the same location and 4 holes (where 2 of them are marked as JP2).</p>
 13432: <p>The best help is the <a href="http://jarick.com.ua/%D0%B2%D1%81%D0%B5-%D0%BE%D1%81%D1%82%D0%B0%D0%BB%D1%8C%D0%BD%D0%BE%D0%B5/25-%D1%81%D1%85%D0%B5%D0%BC%D0%B0-%D0%BA%D0%BB%D0%BE%D0%BD%D0%B0-arduino-uno-r3-%D0%BD%D0%B0-atmega328-%D0%B8-ch340g.html" rel="nofollow noreferrer">schematics</a> for the clone. </p>

<p><a href="https://i.stack.imgur.com/pZnla.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pZnla.jpg" alt="enter image description here"></a></p>

<blockquote>
  <p>1) At number 1 there is on the clone arduino a 12 MHz oscillator? What does it do? And since there is also the regular 16 MHz oscillator I wonder why there are two.</p>
</blockquote>

<p>Lower left on the schematics is the 12 MHz crystal. It is for the CH340G (USB-UART chip).</p>

<blockquote>
  <p>2) At number 2 are 4 holes without any explanation. What is the function?</p>
</blockquote>

<p>Lower middle is the pins X1. They are extra signals from the USB-UART chip (CTS, DSR, R and DCD).</p>

<blockquote>
  <p>3) At 3 there are 12 holes (sorry that only 9 are visible, under the blue/black cable are 4 more holes with silver square around them.</p>
</blockquote>

<p>Upper right on the schematics are the extra pins. This might be handy. </p>

<blockquote>
  <p>4) At 4 there is a SCL and SDA which are used for SPI I think, but these are not on the original Arduino. But the original Arduino has 6 pins at the same location and 4 holes (where 2 of them are marked as JP2).</p>
</blockquote>

<p>The original has an extra ISP pins (ICSP1) for the ATmega16U2. See the <a href="https://www.arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf" rel="nofollow noreferrer">schematics</a>. The clone has the new layout I2C signals extending beyond pin 13.</p>
