This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
CDs don't have circular tracks. They're laid out on a spiral, with
multiple sessions composed of multiple tracks composed of sectors, and the
data in the sectors is interleaved and spread over a large area. The
sector format is standard, but there's more than one standard.
"The nice thing about standards is that you have so many to choose from."
-- Andrew S. Tanenbaum, _Computer Networks_, 2nd ed, p.254
The ability to read certain portions of a CD depends on the CD firmware.
Some CD players aren't capable of understanding multi-session discs or of
reading audio tracks as digital data. Jitter, described in section (2-15),
is also a problem for some drives.
See also section (3-42) on "bit-for-bit" copies.