//The Abstract ComputerFactory to create an Abstract CPU and Memory
public interface ComputerFactory
{
    CPU createCPU();
    Memory createMemory();
}

//Abstract CPU
public interface CPU
{
    string GetCPU();
}

//Abstract Memory
public interface Memory
{
    string GetMemory();
}

//Concrete ComputerFactoryA tp create CPUA and MemoryA
public class ComputerFactoryA : ComputerFactory
{
    public CPU createCPU() { return new CPUA(); }
    public Memory createMemory() { return new MemoryA(); }
}

//Concrete CPUA
public class CPUA : CPU
{
    public string GetCPU() { return "CPUA"; }
}

//Concrete MemoryA
public class MemoryA : Memory
{
    public string GetMemory() { return "MemoryA"; }
}

//client class
using System;
public class Client
{
    //this is a template method; does not depend on the Concrete Factory 
    //and the Concrete classes
    public static void BuildComputer(ComputerFactory factory)
    {
        CPU cpu = factory.createCPU();
        Memory memory = factory.createMemory();
        Console.WriteLine("CPU:{0}", cpu.GetCPU());
        Console.WriteLine("Memory:{0}", memory.GetMemory());
    }    
}

Client.BuildComputer(new ComputerFactoryA());