Oh really?

Are you a software engineer too!

The data on a hard drive is truly random access and because of that it can
be in any order. That's why we have things like disk defragmenters. There is
a file system in place that requires that the entire partition on the hard
drive has a format regardless of the amount of data that is stored there. CD
audio is nothing like the data structures that are stored on a hard drive.
The tracks are most definitely in order on the disk and they can be accessed
simply by moving the laser read head a certain amount to catch the stream
somewhere near the beginning of the track. CD audio was developed WAY before
anyone had the idea of putting a file format and computer data on a CD. Sure
lots of enhancements to the format have come along over the years. I'm
talking about first generation CD.

~James. )


wrote in message
ups.com...

James Lehman wrote:
It is my understanding that Redbook Audio is a digital audio data
storage
system that does not have the likes of a file system, like you would
find on
a data CD. It is more like the grooves on an old LP. The original idea
of a
CD audio player was a digital extension of the idea of the LP. It spins.
It's round. It has a hole in the middle. The tracks on a disk need to be
accessible while the disk is spinning and in any rotation so you can cue
a
track from somewhere near the beginning, not necessarily the exact same
sample every time; much like dropping the needle in the darker grooves
on an
LP. Because there is no file system, it takes some special care to
extract
the audio as a pure digital stream.

That's not correct.

CD audio data is collected into well-defined units that comprise
a hiearchy which certainly qualifies as a random-access, indexable,
seekable (with 100% repeatability) hierarchy.

The smallest addressable unit in a CD is a subcode block, which has
its own sync work, instructions, data, commands and error correction
information. Such a block can define the beginning of a track or index,
which is uniquely and repeatably accessible, just as would the sector
on a harddrive.

The lead-in tracks contain track and index tables that can be read in,
as the vast majority of CD players do. That's why when you put in a CD,
the player will often display immediately how many tracks it finds. It
does not have to read the entire disk to gather this information: it's
all in the index track. Another word for "index track" would
appropriately be "directory." This area includes not only track
subcode block index information, but includes track and index timing
as well.

Once any one entry is known, the drive can be commanded to seek to
the exact location on the disk and start playing (reading) immediately.
It will do so from the same sample every time you command it to do
so. There is no inaccuracy in that respect. You're limited to starting
reading from the beginning of a sub code block, and not anywhere in
the middle, simply because the error correction requires an entire
block to perform its operations.

In all respects, a CD is far more different from an LP than it is
similar, and for more like a hard drive than it is different.