Pros and Cons of amd64 (versus i386).

[Scott Long]

Chris H. wrote:

> Quoting Peter Jeremy <peterjeremy at optushome.com.au>:
> 
>> On Sat, 2006-Apr-08 20:41:36 +0400, Dmitry Morozovsky wrote:
>>
>>> On Fri, 7 Apr 2006, Peter Jeremy wrote:
>>> PJ> Backup your amd64 environment and install i386.  You can re-install
>>> PJ> the amd64 once the testing is finished.  The best benchmark is 
>>> always
>>> PJ> your own application.
>>>
>>> Or, even better, use spare disk or at least spare slice.  Having 
>>> fresh good
>>> backup never hurts though ;-)
>>
>>
>> Note that using different slices may change your results.  All modern
>> disks are faster near the outside (start of the disk) then the inside
>> (I get more than 50% increase from inside to outside on one system).
> 
> 
> My experience(s) seem to indicate the center of the platter results in
> a quicker hit rate. But none the less; this still only further confirms
> your point about the different areas of the platter(s) returning different
> results. It might also be worth noting that the large onboard disk caches
> that come on most modern hard drives will *also* likely help skew the 
> results.
> 
> --Chris H.
> 

Modern disks (I don't know how to define a cutoff to this term,
unfortunately) definitely put more bits onto the outer rim of the
platter than the inner rim.  The days of disks having a fixed number
of sectors per track across the entire platter are long gone.  I was
actually just talking about this with a Maxtor servo engineer the
other day.  I'm still not clear on whether the drive starts recording
at the outer rim or the inner rim of the disk, and that could very well
different between manufacturers.  But, different parts of the disks
do indeed perform differently, both for seek time and for sequential
data thoroughput.  The only way to get a 'fair' comparison is to use
separate identical disks with identical partition layouts for each
of your OS installs.

Scott