CHAPTER 13

710 Chapter 13 Optical Storage
Orange Book
The Orange Book defines the standards for recordable CDs and originally was announced in 1989 by
Philips and Sony. The Orange Book comes in three parts: Part I describes a format called CD-MO
(magneto-optical), which was to be a rewritable format but was withdrawn before any products really
came to market; Part II (1989) describes CD-R; and Part III (1996) describes CD-RW. Note that originally,
CD-R was refered to as CD-WO (write-once), and CD-RW originally was called CD-E (erasable).
The Orange Book Part II CD-R design is known as a WORM (write once read mostly) format. After a
portion of a CD-R disc is recorded, it can’t be overwritten or reused. Recorded CD-R discs are Red
Book and Yellow Book compatible, which means they are readable on conventional CD-DA or CD-
ROM drives. The CD-R definition in the Orange Book Part II is divided into two volumes. Volume 1
defines recording speeds of 1x, 2x, and 4x the standard CD speed; the last revision, dated December
1998, is 3.1. Volume 2 defines recording speeds up to 16x the standard CD speed, and the last version
released, 0.9, is dated December 2000.
The Orange Book Part III describes CD-RW. As the name implies, CD-RW enables you to erase and
overwrite information in addition to reading and writing. The Orange Book Part III CD-RW definition
was broken into two volumes. Volume 1 defines recording speeds of 1x, 2x, and 4x times the standard
CD speed; the latest version, 2.0, is dated August 1998. Volume 2 defines recording speeds from 4x to
10x standard CD speed, and is sometimes refered to as high-speed CD-RW; the latest version, 1.0, is
dated May 2000.
Besides the capability to record on CDs, the most important features instituted in the Orange Book
specification is the capability to do multisession recording.
Multisession Recording
Before the Orange Book specification, CDs had to be written as a single session. A session is defined as
a lead-in, followed by one or more tracks of data (or audio), followed by a lead-out. The lead-in takes
up 4,500 sectors on the disc (1 minute if measured in time or about 9.2MB worth of data). The lead-in
also indicates whether the disc is multisession, and what the next writable address on the disc is (if
the disc isn’t closed). The first lead-out on a disc (or the only one if it is a single session or Disk At
Once recording) is 6,750 sectors long (1.5 minutes if measured in time or about 13.8MB worth of
data). If the disc is a multisession disc, any subsequent lead-outs are 2,250 sectors long (0.5 minutes in
time or about 4.6MB worth of data).
A multisession CD has multiple sessions, with each individual session complete from lead-in to leadout.
The mandatory lead-in and lead-out for each session does waste space on the disc. In fact, 48 sessions
would literally use up all of a 74-minute disc even with no data recorded in each session!
Therefore, the practical limit for the number of sessions you can record on a disc would be much less
than that.
CD-DA and older CD-ROM drives couldn’t read more than one session on a disc, so that is the way
most pressed CDs are recorded. The Orange Book allows multiple sessions on a single disc. To allow
this, the Orange Book defines three main methods or modes of recording:
■ Disk-at-Once (DAO)
■ Track-at-Once (TAO)
■ Packet writing
Disc-at-Once
Disc-at-Once means pretty much what it says: It is a single- session method of writing CDs in which
the lead-in, data tracks, and lead-out are written in a single operation without ever turning off the