DISC SIZE AND CAPACITY
What are the physical sizes of CD-R and CD-RW discs?
CD-R and CD-RW discs come in standard 12 cm (120 mm) and 8 cm (80 mm) sizes.
The most popular is the larger 12 cm type which has the same physical dimension
as most commercial audio CDs and computer software CD-ROMs. 8 cm discs are less
common but, thanks to their smaller size, are gaining popularity for use in consumer
electronic devices such as portable compressed digital audio players, digital
still image cameras and data storage products like miniature CD recorders.
What about business card CD-R and CD-RW discs?
Beyond the conventional 8 cm and 12 cm sizes some manufacturers offer discs shaped
like business and credit cards or in other novelty forms. These do not conform
with Orange Book specifications and, as a result, may not write and play back
in all recorders or reading devices. Following manufacturer instructions is always
the best course.
What capacities of blank CD-R and CD-RW discs are available?
Manufacturers commonly express disc capacity in terms of how much Red Book digital
audio (in minutes) and computer data (in megabytes) a disc can contain. Historically,
63 minute/550 MB (12 cm) and 18 minute/158 MB (8 cm) discs were once available
but are now rendered obsolete by advances in recording technology. Currently,
74 minute/650 MB, 80 minute/700 MB (12 cm) and 21 minute/185 MB (8 cm) discs
are the market standards.
What about 34, 90 and 99 minute CD-R discs?
A few media manufacturers have recently introduced 34 minute/300 MB (8 cm), 90
minute/790 MB and 99 minute/870 MB (12 cm) CD-R discs. To achieve these higher
capacities such discs do not conform to Orange Book specifications and, as a
result, may not write in all recorders, be accessible to all software or readable
in all players and drives. Using 34, 90 and 99 minute CD-R discs is therefore
How much information can actually be stored on CD-R and CD-RW discs?
The amount of information that can be written is determined by the disc’s
recording capacity as well as the physical and logical formats used.
Each of the five main CD physical formats devotes a different amount of space
to user data (audio = 2,352 bytes/block, CD-ROM Mode 1 = 2,048 bytes/block, CD-ROM
Mode 2 = 2,336/bytes/block, XA Form 1 = 2,048 bytes/block, XA Form 2 = 2,324
bytes/block). For any given data format disc capacity can be calculated by multiplying
the appropriate user data area size by the CD data transfer rate of 75 blocks
per second by 60 seconds by the minute size of disc. For example, a 80 minute
disc written in CD-ROM Mode 1 format: user data area of 2048 bytes/block x 75
blocks/second = 153,600 bytes/second x 60 seconds = 9,216,000 bytes/minute x
80 minutes = 737,280,000 bytes. This rounds to roughly 700 MB (dividing by 1,024
to convert into KB and again by 1,024 to convert into MB). It should be noted,
however, that in the real world capacity can vary slightly among discs from different
For discs written with computer data the logical format used also consumes space
available for user information. For example, the overhead for the first session
of a multisession disc consumes 22 MB of space and each subsequent session thereafter
uses 13 MB. And in the case of CD-RW discs which are formatted for random packet-writing,
usable capacity is reduced by roughly 23%.
CD-R and CD-RW Disc Capacities
(capacities indicated in bytes)
What is the difference between 74 and 80 minute discs?
The only meaningful difference between most 74 and 80 minute discs is their
storage capacity. Typically, this increase in usable space is achieved
by tightening the coils of the pregroove (track pitch). This allows the
disc to accommodate a longer pregroove and therefore a larger recordable
Are there any compatibility issues when using 80 minute instead of 74 minute
Originally, 80 minute discs were specialized products for use in audio
premastering studios but now have become commonplace and compatible with
most software, recorders, readers and players. In some instances, however,
older recorders and premastering software must be upgraded to accommodate
80 minute discs. It is, therefore, advisable to check with the manufacturers
of your products and ensure that the latest versions of software and firmware
are being used.
What is overburning?
Overburning (sometimes called oversizing) is the ability to write beyond
the manufacturer’s declared capacity on a CD-R or CD-RW disc. This
is accomplished by using the disc’s Lead-Out Area (reserved to indicate
to a reading device that the end of the data has been reached) to store
the additional user information. Although some recorders and premastering
software packages have the ability to overburn a disc the practice is not
permitted by Orange Book standards. Overburning might affect product warranties
and result in lost data so it is not recommended.