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Re: [OT] CD-R Requirements: Conspiracy

On Sat, Nov 23, 2002 at 03:39:32AM +0000, Pigeon wrote:
> OK, but what about the hard drive? In both cases the head has to track
> over the preceding sectors and switch into write mode when it gets to
> the right sector to be written. OK, so one's magnetic, one's optical,
> but the head servos are doing the same thing. The spiral track on a CD
> means you basically have to "pick the track up" a few rotations behind
> where you need to start writing so you've got time to sync in; not a
> problem. And it's the same problem as starting a new session on a
> multisession CD, or packet writing. It's only gonna be awkward if the
> laser drive is so screwed that it burns garbage for the first few
> sectors after you put it into write mode.

HDDs have concentric tracks.  CDs have spiral tracks.  Therefore,
tracking on a CD platter is harder.  The head servos are not doing the
same thing.

HDDs spin at a much higher rate than do CDs.  Therefore, latency is
not as big of an issue with HDDs.

HDDs read and write magnetic ones or zeroes.  If you "screw up" and
reverse the sense of a bit on an HDD, you can repair[1] it.  Not
possible on a CD-R[2].

You claim it's a simple matter of backing up and picking up where you
left off.  On an HDD this is trivial; you simply wait for your sector
to come round again.  On a CD you have _one chance_ to "pick up where
you left off"; if you miss it you can't wait for the CD to spin round
again; the track is a spiral!  You must again backtrack and try to
find the next sector.  If you "miss" and start in the wrong place, you
are screwed.

I am reminded of a quote: Never attribute to malice that which can be
described by sheer incompetence.  Hardware manufacturers are always
producing junk; for the most part the market corrects these flaws.  The
first CD writers were all SCSI, slow, and expensive.  People
complained.  Thus we got IDE CD writers.  People were happier about the
price but still unhappy with performance and reliability.  The CD
writers got faster.  Now reliability was really an issue due to buffer
under-runs.  People complained.  Enter the "burn-proof" CD writer.  Of
course there are still a load of non-burn-proof CD writers out there;
manufacturing facilities do not retool overnight.

[1] Of course if you write the wrong sector you're probably screwed as
far as the original data is concerned.

[2] Even a CD-RW has to be more or less bulk-erased before you can
write on it again.

Nathan Norman - Incanus Networking mailto:nnorman@incanus.net
  Never interrupt your enemy when he is making a mistake.
          -- Napoleon Bonaparte

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