Philips CDD522 Operating Instructions Manual page 35

The only problem was its manufacturing process using
molds to stamp the disks. Small quantities couldn't be
produced, let alone piece-wise reproduction.
In 1992, Philips introduced the CD Recordable. With it
came a new Standard, The Orange Book. The CD-R
makes it possible to record data and audio on a special
disk. It does not allow ERASURE of info. Once written,
no way back.
That special disk when BLANK has none of the elements
we just discussed: No Tracks, Subcode, Lead-in, Lead-
Out or Sectors. It doesn't even have a groove, since
there are no pits (Precisely these are to be recorded !).
Of course, it does have a structure (the CD-R has to know
where it is on the disk, even when its blank). On that disk
you'll find (or at least the CD-R will) a PRE-GROOVE.
This Pre-groove is a small, continuous, undeep gutter, laid
on the disk in a spiral form (like the original string of
bumps on a stamped disk).
The spiral form of the pre-groove exhibits a small jitter
that, when the disk is rotated at the correct linear velocity,
has a frequency of 22.05 KHz. This Wobble, as the jitter
is called, is used by the CD-R for speed control and pre-
groove tracking.
The CD-R needs more than that to know were it is, so the
22.05 KHz Wobble is FM-modulated with time information,
the so-called ATIP (Absolute Time In Pre-groove). This
time runs continuously from the beginning to the end of
the pre-groove.