Two students ask:

    Dear Prof Patt,

    This is ********* and ************* of your EE306 class.  Regarding 
    Questions 6 and 7d on PS3, we do not understand what you mean by the 
    necessary number of bits to access the memory.  From our knowledge 
    of memory so far, we only know what address space and addressability 
    are.  Could you describe (or refer to a text example of) the relation 
    between the necessary number of bits to access the location and the 
    addressability of the memory?  As for 7d, we need to better understand 
    the correlation between the number of bits to access the location and 
    the number of locations.

        Sincerely,

	<<names withheld>>


Rather than just give you the answer, let me walk you through it a bit.

You are correct, you only know about address space and addressability.  
Think about what address space refers to.  Think also about what 
addressability refers to.  If you do, I think you will come to the 
realization pretty quickly about the relationship between the number 
of bits necessary to access the memory location and its addressability.  
What was the addressability of the 2^2 by 4 memory we talked about in 
class?  What is its relationship to the number of locations?

As to the number of bits required to access the location and the number of
locations:  The number of bits required to access the location is the number 
of bits required to differentiate that location from all other locations. 
We call that set of bits the ADDRESS of the memory location.

In the memory example we did in class (Figure 3.20 in the book), how many 
bits did we need to access each location?  How many locations were there?

A couple of other things, while I have your attention.  First, a memory 
location and a memory entry -- synonyms, the two words *location* and 
*entry* are used interchangeably.  Both words refer to that particular 
thing that is identified by its address, and contains some fixed number 
of bits.  The number of bits at each address is the memory's addressability.

Thing 2: I am concerned that some of you are not reading the book.  If you 
have a question about the meaning of a word or a phrase, it is very likely 
that the answer to that question is somewhere in the book.  A little reading 
should go a long way in supplementing what I talk about in class.  The book 
should be your first line of attack, when you find yourself stuck wondering 
what a question is asking you.  

Yale Patt