user7908: I bought a 16Hertz Uno R3 Board. When I installed the driver and the Arduino IDE,  in the IDE`s menu I saw:            

Tools -> Board -> Arduino Uno

was selected by default which is great, but...     

Tools -> Port -> COM3(Arduino Mega or Mega 2560)

was selected by default which I think might be some kind of misunderstanding... 
When I chose: 

Tools -> Board -> Arduino Mega or Mega 2560

On that tools menu appeared new menu "Processor" with two options:   

Tools -> Processor -> ATmega2560 (Mega 2560)

which was selected by default and there was another option

Tools -> Processor -> ATmega1280

When I restore Tools -> Board settings back to "Arduino Uno" the "Processor" menu with the two options disappeared and Tools -> Port setting did not changed!
If you take my board and look at the Microcontroller there is written: 

ATMEGA328P-PU

Also on that board is written: 

16HzUNO

I need to know:   

What does 16Hz mean? Does it mean the clock or frequency of this
Microcontroller? I think it does not, if I try to find out details of my Microcontroller on the rs-online site, there is written:     


ATMEGA328P-PU, 8 bit AVR Microcontroller 20MHz 1 kB, 32 kB Flash, 2
  kB RAM, I2C 28-Pin PDIP


Why was there "COM3(Arduino Mega or Mega 2560)" written on the
Port's menu?
Is my 16Hz Uno R3 and the Arduino Uno R3 board the same? Which one
is better? When one of those is better?
Does the standard Arduino Uno R3 board have the same ATMEGA328P-PU
Microcontroller?


user6969: 
Every Arduino is using a quartz crystal in order to get the frequency needed. ATmega328 can handle up to 20 MHz
??
Yes. You can't run the microcontroller by itself. It has an internal oscillator but none is using it. So basically you will have a 16 MHz crystal.
Pretty much the Arduino Uno, Nano, Mini and few others have the ATmega328P.
Note that the -PU -AU at the end defines the package. So they're the same.

Arduino Mega, Leonardo, Micro, Due use other chips.

user6936: You need to have a look at the Arduino comparison table. This shows that all Arduino Uno boards run at 16 MHz. It seems that you have fallen for the marketing on the page for the Uno kit that you provided.
Also, which version of the IDE are you running? You should upgrade to the latest version, which is currently, at the time of writing, version 1.6.1.
To answer your questions in turn:

"16Hz" is the brand name and has nothing whatsoever to do
with the speed, which is actually 16 Mega Hertz. "Clock" and
"Frequency" refer to the same thing. 16 MHz is the clock frequency
of the board, and is the speed at which the ATmega328 runs at.
The RS Online link does indeed state 20 MHz, but that is merely the
maximum speed at which the ATmega328 can run at. The Uno under clocks it at 16 MHz.
The Ports menu will show you a number of possible devices, Arduino Uno should be one of them (which is the one you should select) and three items below that will be Arduino Mega or Mega 2560 (which you should ignore, you do not have a Mega board1). Unfortunately the Arduino site only shows the Mac menu, even on the Windows guide



which is no help to you, assuming that you are running the Arduino IDE on Windows. You should actually see this in the Board menu:



and this in the Port menu:



As you can see, there should be no mention of the microcontroller in the Port menu.
The 16Hz branded Uno and the Arduino Uno are to all intents and purposes the same and as I state in the first line, the 16 MHz Uno is exactly the same as a regular Uno, it is just marketing.
Both the 16Hz and the Arduino Uno have a ATmega328 and the Mega board has a ATmega2560. Again, check the Arduino comparison table to see the variety of the boards and their respective microcontrollers.

I hope that answers your questions.

1 If you do chose the Arduino Mega or Mega 2560 option, in the Board menu, then indeed there will be an additional Processor menu. However, this is irrelevant in your case, as you do not have a Mega board, and so you need to chose the Uno in the Board menu. If you do so, then the Processor menu will disappear, as it is not needed for the Uno. 

7908: <p>I bought a <a href="http://www.16hertz.com/product/uno-r3-kit-ultimate-arduino-compatible/" rel="nofollow">16Hertz Uno R3 Board</a>. When I installed the driver and the Arduino IDE,  in the IDE`s menu I saw:            </p>

<blockquote>
  <p>Tools -> Board -> Arduino Uno</p>
</blockquote>

<p>was selected by default which is great, but...     </p>

<blockquote>
  <p>Tools -> Port -> COM3(Arduino Mega or Mega 2560)</p>
</blockquote>

<p>was selected by default which I think might be some kind of misunderstanding... </p>

<p>When I chose: </p>

<blockquote>
  <p>Tools -> Board -> Arduino Mega or Mega 2560</p>
</blockquote>

<p>On that tools menu appeared new menu "Processor" with two options:   </p>

<blockquote>
  <p>Tools -> Processor -> ATmega2560 (Mega 2560)</p>
</blockquote>

<p>which was selected by default and there was another option</p>

<blockquote>
  <p>Tools -> Processor -> ATmega1280</p>
</blockquote>

<p>When I restore Tools -> Board settings back to "Arduino Uno" the "Processor" menu with the two options disappeared and Tools -> Port setting did not changed!</p>

<p>If you take my board and look at the Microcontroller there is written: </p>

<blockquote>
  <p>ATMEGA328P-PU</p>
</blockquote>

<p>Also on that board is written: </p>

<blockquote>
  <p>16HzUNO</p>
</blockquote>

<p>I need to know:   </p>

<ol>
<li>What does 16Hz mean? Does it mean the clock or frequency of this
Microcontroller? I think it does not, if I try to find out details of my Microcontroller on the <a href="http://ie.rs-online.com/web/p/microcontrollers/6962260/" rel="nofollow">rs-online site</a>, there is written:     </li>
</ol>

<blockquote>
  <p>ATMEGA328P-PU, 8 bit AVR Microcontroller 20MHz 1 kB, 32 kB Flash, 2
  kB RAM, I2C 28-Pin PDIP</p>
</blockquote>

<ol start="2">
<li>Why was there "COM3(Arduino Mega or Mega 2560)" written on the
Port's menu?</li>
<li>Is my 16Hz Uno R3 and the Arduino Uno R3 board the same? Which one
is better? When one of those is better?</li>
<li>Does the standard Arduino Uno R3 board have the same ATMEGA328P-PU
Microcontroller?</li>
</ol>
 6969: <ol>
<li><p>Every Arduino is using a quartz crystal in order to get the frequency needed. ATmega328 can handle up to 20 MHz</p></li>
<li><p>??</p></li>
<li><p>Yes. You can't run the microcontroller by itself. It has an internal oscillator but none is using it. So basically you will have a 16 MHz crystal.</p></li>
<li><p>Pretty much the Arduino Uno, Nano, Mini and few others have the ATmega328P.
Note that the <code>-PU</code> <code>-AU</code> at the end defines the package. So they're the same.</p></li>
</ol>

<p>Arduino Mega, Leonardo, Micro, Due use other chips.</p>
 6936: <p>You need to have a look at the <a href="http://arduino.cc/en/Products.Compare" rel="nofollow noreferrer">Arduino comparison table</a>. This shows that <em>all</em> Arduino Uno boards run at 16&nbsp;MHz. It seems that you have fallen for the marketing on the <a href="https://web.archive.org/web/20150104015236/http://www.16hertz.com/product/uno-r3-kit-ultimate-arduino-compatible/" rel="nofollow noreferrer">page for the Uno kit</a> that you provided.</p>

<p>Also, which version of the IDE are you running? You should upgrade to the latest version, which is currently, at the time of writing, version 1.6.1.</p>

<p>To answer your questions in turn:</p>

<ol>
<li>"<strong>16Hz</strong>" is the <em>brand name</em> and has nothing whatsoever to do
with the speed, which is actually 16 <strong>Mega</strong> Hertz. "Clock" and
"Frequency" refer to the same thing. 16 MHz is the clock frequency
of the board, and is the speed at which the <strong>ATmega328</strong> runs at.
The RS Online link does indeed state 20&nbsp;MHz, but that is merely the
<em>maximum</em> speed at which the <strong>ATmega328</strong> can run at. The Uno under clocks it at 16 MHz.</li>
<li><p>The <strong>Ports</strong> menu will show you a number of possible devices, <strong>Arduino Uno</strong> should be one of them (which is the one you should select) and three items below that will be <strong>Arduino Mega or Mega 2560</strong> (which you should ignore, you do not have a Mega board<sup>1</sup>). Unfortunately the Arduino site only shows the Mac menu, even on <a href="http://www.arduino.cc/en/Guide/Windows#toc7" rel="nofollow noreferrer">the Windows guide</a></p>

<blockquote>
  <p><a href="https://i.stack.imgur.com/ikeJV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ikeJV.png" alt="Mac Arduino Tools menu"></a></p>
</blockquote>

<p>which is no help to you, assuming that you are running the Arduino IDE on Windows. You should actually see this in the <strong>Board</strong> menu:</p>

<blockquote>
  <p><a href="https://i.stack.imgur.com/qttd5.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qttd5.png" alt="Windows Arduino Tools Board menu"></a></p>
</blockquote>

<p>and this in the <strong>Port</strong> menu:</p>

<blockquote>
  <p><a href="https://i.stack.imgur.com/BrjgA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BrjgA.png" alt="Windows Arduino Tools Port menu"></a></p>
</blockquote>

<p>As you can see, there should be no mention of the microcontroller in the <strong>Port</strong> menu.</p></li>
<li><p>The 16Hz branded Uno and the Arduino Uno are to all intents and purposes the same and as I state in the first line, the 16 MHz Uno is <em>exactly</em> the same as a regular Uno, it is just marketing.</p></li>
<li>Both the 16Hz and the Arduino Uno have a <strong>ATmega328</strong> and the Mega board has a <strong>ATmega2560</strong>. Again, check the <a href="http://arduino.cc/en/Products.Compare" rel="nofollow noreferrer">Arduino comparison table</a> to see the variety of the boards and their respective microcontrollers.</li>
</ol>

<p>I hope that answers your questions.</p>

<hr>

<p><sup>1</sup> If you <em>do</em> chose the <strong>Arduino Mega or Mega 2560</strong> option, in the <strong>Board</strong> menu, then indeed there will be an additional <strong>Processor</strong> menu. However, this is irrelevant in your case, as you do not have a Mega board, and so you need to chose the Uno in the <strong>Board</strong> menu. If you do so, then the <strong>Processor</strong> menu will disappear, as it is not needed for the Uno. </p>
