Is the public class object in scripts only a reference of the game object's component?

I am new to both unity3D and C#. After creating my first “Hello world” program, I have a question about the public class object in script.
In the level, I have two game objects (A & B). There are two scripts attached to these objects separately. The script A is as follows:

public class ScriptA : MonoBehaviour

    public int m_value1;
    public int m_value2;
    public int m_value3;

    // Use this for initialization
    void Start()
        m_value1 = 0;
        m_value2 = 0;
        m_value3 = 0;

and the script B is:

public class ScriptB : MonoBehaviour {
    public ScriptA m_objectA;
    public int m_value1 = 0;
    public int m_value2 = 0;

I am now wondering that whether the m_objectA in scriptB only a reference of object A or the data of object A is stored in two places in my memory. I am really worried about this problem especially when I want to use object A to store enormous data. Thanks a lot!

Classes stored in variables are only references. If you need different instances out of one, you will need to copy everything from the class. There are multiple solutions, one of them is deep copy. But do not do that with mono behaviours, unless you want to copy component to different object.