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but very briefly.

A drive with a higher speed rating would draw more power while spinning
up, but would probably use the same amount while actually doing work.
While installing Linux on a different system with an Asus 52x CD-ROM drive,
I noticed the load for the entire system went from around 50W when idle to
a fairly stable 90W while doing CD media verification.  How much of that
was the drive and how much was the CPU is unclear -- the load on the system
would go from 50W to 70W when quickly raising and lowering a window under
X11 -- but it's clear that there's more to the story than the drive itself.

My earlier hypothesis -- that CD recorders draw significantly more power
when recording -- appears to be incorrect.  There have been cases where
people could do test writes but not actual writes, and solved the problem
by upgrading their power supply.  However, this appears to have more to
do with the power supply's stability than changing load requirements.
The power supply that fixed the problem may have been more reliable, or
perhaps the old one was always overtaxed and the problem didn't manifest
itself until something requiring precise power management was in use.


Subject: [5-27] Will the laser in my drive wear out?
(2002/12/02)

Yes, eventually.  Depending on a number of factors, though, it's quite
possible that your device will suffer mechanical breakdown or simply
become obsolete before that happens.

There are many different ways to construct a laser diode.  Different
approaches result in different wavelengths, maximum power levels, and
lifetimes.  The lifetime of a laser is usually measured as MTTF (Mean
Time To Failure) at a particular power level and ambient temperature
(e.g. 10,000 hours at 5mW and 50 degrees Celsius).

Higher power levels mean higher heat dissipation -- the optical conversion
efficiency of a laser diode is around 30% -- and in the semiconductor world,
more heat usually equates to shorter lifetime.  Recording for an hour at high
speed will take a greater toll on the laser than playing a CD for an hour.

The bottom line is, there really isn't anything you can do to make the
laser last longer.  It'll last a very long time when used to read CDs,
so there's no point in reserving the drive just for recording.  It might
last a little longer if you use lower recording speeds, but if you're
willing to do that then why pay for a high-speed recorder?

Sony Semiconductor's "Laser Diode Guide" is available from
http://www.sony.net/Products/SC-HP/laser/guide.html.

Laser diodes can suffer catastrophic failure (they suddenly stop working)
or gradual degradation (reduced optical power for a given input power
level).  The power calibration sequence ((4-13), (5-11)) automatically
adjusts the power supplied to the laser for a given disc and write speed,
so reductions in output are compensated for automatically.  However,
if the laser's efficiency is reduced, more DC power must be supplied,
more heat is generated, and the likelihood of failure increases.

For a discussion of laser diode reliability, see
http://www.bostonlaserinc.com/art1.php.


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