Explanation : A CD-ROM is a pre-pressed optical
compact disc that contains data. Computers
can read-but not write to or erase. It has
the capacity of 194 MiB (8 cm), 650-900
MiB (12 cm). A read-only DVD disc used
to permanently store data files. It has the
storage capacity of 4.7 GB (single-sided,
single-layer - common) 8.5 GB (single-
sided, double-layer) 9.4 GB (double-sided,
single-layer) 17.08 GB (double-sided,
double-layer).
Blu-ray or Blu-ray Disc (BD) is a digital
optical disc data storage format. It was
designed to supersede the DVD format, and
is capable of storing several hours of video
in high-definition (HDTV 720p and 108Op)
and ultra high-definition resolution (216Op).