Why does the 20 bit address bus determine the storage space of 1MB

Why? 20 The bit address bus determines that the storage space is ：

instead of

First listen to a story , Please bring in the settings completely ：

Our family is a pig farm , My pig farm has only 8 A room , The specifications of each room are fixed , Only eight pigs can be raised

Now I want to give it to the pig farm 8 Room number , I have a book like this ：

（ A scoring book like a basketball game , The difference is , I can only write 0 and 1 Two figures , To show the end 8 A room , I need three pieces to turn ）

So the room number is

000

001

010

011

100

101

110

111

Now I ask you , From my three bars indicating the room number and the situation that there are eight pigs in each room , Can you see how many pigs there are in my family ？

You will answer ：

8 A room , A room 8 Pigs , Namely 8*8=64 Pigs

Because we assume that in this world , A room can only hold eight pigs , No more, no less

therefore , in the course of time , When people from different pig farms communicate , No longer say how many pigs I have , But how many rooms do I have

Everyone knows that you have 5 A room of pigs means you have 5*8 = 40 Pigs .

And in the computer ：

The smallest data storage unit in a computer is byte, That is to say a standard “ room ” Size is 8 Bit binary number , namely 1Byte（1Byte = 8bit）

In the case of pigs , To express the end 8 A room , need 3 Zhang Tiao ：

therefore , Let's change the sentence again ：

Then it becomes a computer term ：

After converting into storage space ：

20 The bit address bus determines that the storage space is ：（ B = Byte ）