[geeks] Advice on buying a new Mac

[Jonathan C. Patschke]

On Mon, 13 Nov 2006, Patrick Giagnocavo wrote:

> No, if you mean "will it pull data off the disk as fast".  Reason is
> twofold:

<snip>

> 2. the physical drive platter is smaller, thus, even though rotating at
> the same speed, the swept area (whatever the technical term is) is less
> than a larger platter.

It takes more time to traverse a smaller distance?

As far as I know, most drives still use a concentric sector layout, so
the number of sectors per angle is a constant across all tracks.  The
density of the inner tracks is bound by the coercivity of the medium,
and the density of the outer tracks is limited by the rotational speed
of the medium.  Packing in the absolute maximum amount (through a single
spiraling track of sectors like CDs use) of storage would complicate
drive electronics significantly.

For what it's worth, a good number of current-model medium-capacity 3.5"
SAS drives use 2.5" HDAs.  Notebook drives aren't slow because of the
physical size[0]; they're slow because they can't be permitted to
dissipate as much heat as a WD Raptor or Seagate Cheetah.  It's only
been recently, though, that the capacity of the 2.5" HDAs has approached
something usable in a server or RAID shelf.  If you only -need- 160GB of
storage per drive, why not save some power by spinning smaller platters?


[0] Consider this:  The slowest moving parts of the disk have less
     travel as the diameter of the platters decreases.
-- 
Jonathan Patschke  ) "Some people grow out of the petty theft of
Elgin, TX         (   childhood.  Others grow up to be CEOs and
USA                )  politicians."              --Forrest Black