79
a disc spins a constant speed, with the result that the
tracks nearest the center pass under the reading head at
a lower speed that the tracks nearer to the outer edge of
the disk. This is the approach normally taken in mag-
netic disks, so the sectors on the disk are physically
shorter near the center and longer near the edge of the
disc. CAV is also used for Magneto-Optical discs and
CD-R/RW discs (reading only)
Constant Linear Velocity A rotation mode in which
the speed of rotation is variable, so that all data sectors
pass under the reading head at exactly the same speed;
the rotation rate of the disc is faster when the reading
head is near the center of the disc, and slower as the
reading head moves further from the center of the disc;
sector size is constant. Used with Compact Discs for
recording and slower speed reading/playing.
Cost-Per-Megabyte A measure of the expense in-
curred per megabyte of usable storage received. The
common formula is to divide the cost of the drive-and
the case of the removable media, the cost of the media-
by the number of megabytes. This measure alone ig-
nores performance issues, which has a significant im-
pact on the selection of storage method.
Cyclability A measure of how many times a CD-RW
disc can be re-written. Currently, cyclabilty for CD-
RW is set at 1,000 cycles (rewrites to any one sector)
Direct Overwrite (DOW) A method of recording new
data onto a CD-RW disc directly over the existing data.
This saves time since the disc does not need to be pre-
erased prior to recording new data. Some Magneto-
Optical systems are capable of DOW.
Directory In the logical format of a disc, a “branch” of
the information tree containing other directories (sub-
directories) and/or files.
Glossary
