Sony MZ-R90 - Manual (Page 52)

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How the MiniDisc got so small
The 2.5-inch MiniDisc, encased in a plastic
cartridge that looks like a 3.5-inch diskette
(see illustration above), uses a new digital
audio compression technology called
ATRAC (Adaptive TRansform Acoustic
Coding). To store more sound in less space,
ATRAC extracts and encodes only those
frequency components actually audible to
the human ear.
Quick Random Access
Like CDs, MDs offer instantaneous random
access to the beginning of any music track.
Premastered MDs are recorded with location
addresses corresponding to each music
selection.
Recordable MDs are manufactured with a
“User TOC Area” to contain the order of the
music. The TOC (Table of Contents) system
is similar to the “directory management
system” of floppy disks. In other words,
starting and ending addresses for all music
tracks recorded on the disc are stored in this
area. This lets you randomly access the
beginning of any track as soon as you enter
the track number (AMS), as well as label the
location with a track name as you would a
file on a diskette.
Shock-Resistant Memory
One major drawback of optical read systems
is that they can skip or mute when subjected
to vibration. The MD system resolves this
problem by using a buffer memory that
stores audio data.
User TOC Area Music Data
Contains the order and start/end
points of the music.