[Pgubook-readers] Initial feedback

[Xavier Noria]

I have started the book and my first impression is that it is just 
great. It addresses the fundamental doubts I have had for several years 
(I program in several languages but my low-level ends in C). The 
introductory chapters are very well written and the concepts clearly 
introduced. I had played with MIX and had readed some stuff but this 
description has put everything together very well for me.

There was a couple of things in chapter 2 I think it would be worth to 
mention as a matter of feedback, not sure whether this is on topic but 
here they go:

* The data bus is introduced as a mean to fetch data from memory 
(page7, 2nd paragrapgh). Right before, however, it is said that the CPU 
fetches the content in the address stored in the program counter. In 
that context it is emphasized that memory cells are of equal type, and 
that what differs is the way the numbers are interpreted, which makes 
me wonder whether the data bus is used as well in that case, and if not 
how is the instruction actually fetched and why the difference.

* In that introduction there is a conceptual separation between memory 
and CPU. But because of that the sentence "On x86 processors, a byte is 
a number between 0 and 255" surprised to me. It made me wonder why the 
processor, which until now was something kind of independent, 
determines the size of the cells and not, say, the memory manufacturer.

* I appreciated the comment about the simplifications being made and 
the list of keywords to find further information.

-- fxn