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Subject: RE: Re[2]: Hard Disk Question
From: Fred Maxwell (
Date: 2004-05-08

Roland wrote:

> i`m no mechanic - but - regarding the new 1.8" HDD models:
> shouldn`t such HDDs be more robust than a 2.5" HDD in general ?
> Less weight means less forces - so probably a tiny HDD is more
> robust than a bigger HDD ?

You are a better mechanic than you give yourself credit for. There are
several mechanical factors at work:

A larger hard drive requires a longer arm to hold the head. That means
that, in general, the arm has more mass.

Because the arm is longer, there is also greater leverage when it receives a

Since a 1.8" hard drive has a shorter and lighter arm, it's, in general,
going to be more shock-resistant.

Here's where things get interesting: The primary reason that mass is kept
down on the arm and head assemblies is to allow faster seeks (the head
moving from one track to another). This is important when reading and
writing randomly placed data as one normally does when using a computer.

In the case of an MP3 player, the needs are totally different. There is a
specific rate at which you can use the data (e.g., 128kbps, 192kpbs, etc.)
and as long as the hard drive can seek and read fast enough to keep a buffer
of audio data filled, you're golden. Therefore, it would be possible to
design a slower, but more rugged, hard drive that would be well-suited to a
portable MP3 player -- even though it would have too slow an average access
time to be satisfactory in a personal computer. (It would still be plenty
fast for reading directories on the player).

The next step in making an optimized MP3 player hard drive is to reduce
power consumption. The best ways to do that are

1. Reduce rotational mass and centralize it more (translation, smaller
diameter, lighter platters). That reduces current consumption to spin the
platters up to speed.
2. Reduce the drive RPMs. You just don't need high rotational speed to
keep up with MP3 data rates.

  Fred Maxwell


Page was last modified "Jan 10 2012" The Rockbox Crew