关于IComparable<>问题.

本人在看programming C#(中文版) 电工出版 上面看到这样一行.
public class Node<T>:IComparable<Node<T>> where T:IComparable<T>{ private T data;  ...}
书上是这样描述的:实现一个简化的可排序单链表.表是由多个结点组成,没个结点必须保证添加到其上的类型实现IComparer.
我想问的就是.这一行代码.如果写成这样的话.会有什么不同呢?  
public class Node<T>:IComparable<T> where T:IComparable<T>{private T data;  ...}
还有就是他里面有一个私有变量data..T暂时是不不知道的类型.如果传进去的是引用类型也能这样直接用"private"定义吗?
为了大家看得更清楚.我还是把Node<T>的全部代码都弄上来.
public class Node<T> : IComparable<Node<T>> where T : IComparable<T>
    {
        private T data;
        private Node<T> next = null;
        private Node<T> prev = null;        public Node(T data)
        {
            this.data = data;
        }        public T Data{get {return this.data}}        public Node<T> Next
        {
            get { return this.next; }
        }        public int CompareTo(Node<T> rhs)
        {
            return data.CompareTo(rhs.data);
        }        public bool Equals(Node<T> rhs)
        {
            return this.data.Equals(rhs.data);
        }        public Node<T> Add(Node<T> newNode)
        {
            if (this.CompareTo(newNode) > 0)
            {
                newNode.next = this;
                if (this.prev != null)
                {
                    this.prev.next = newNode;
                    newNode.prev = this.prev;
                }
                this.prev = newNode;
                return newNode;
            }
            else
            {
                if (this.next != null)
                {
                    this.next.Add(newNode);
                }
                else
                {
                    this.next = newNode;
                    newNode.prev = this;
                }
                return this;
            }
        }        public override string ToString()
        {
            string output = data.ToString();
            if (next != null)
            {
                output += ", " + next.ToString;
            }
            return output;
        }
    }