patchProgramming from the Ground Up Book - Patches: patch #2591, Data Bus Clarifications

 
 

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patch #2591: Data Bus Clarifications

Submitted by:  None
Submitted on:  Thu 05 Feb 2004 09:48:17 PM UTC  
 
Category: NonePriority: 1 - Later
Status: NonePrivacy: Public
Assigned to: NoneOriginator Email: -unavailable-
Open/Closed: Open

Sat 20 Mar 2004 06:45:23 PM UTC, comment #1:

Quoted:
-------------
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.
-------------

The reason for this, IMO, is that they need a standard. Think of how much extra work the cpu would have to do to figure out how big the memory sizes are. Mixing different memory stick manufacturers would create havoc on the cpu. So instead, the cpu decides that a byte is 0 to 255 then it knows for certain that when it checks memory, regardless of the manufacturer, it knows where and how much.

Matt Robineau <vexer>
Thu 05 Feb 2004 09:48:17 PM UTC, original submission:

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.

Anonymous

 

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