CHAPTER 13

732 Chapter 13 Optical Storage
■ Column 1. Indicates the advertised drive speed. This is a constant speed if the drive is CLV or a
maximum speed only if CAV (most DVD-ROM drives are CAV).
■ Columns 2 and 3. Indicate how long it would take to read a full disc (single- or dual-layer) if the
drive were CLV. For CAV drives, those figures are longer because the average read speed is less
than the advertised speed. The fourth column indicates the data transfer rate, which for CAV
drives is a maximum figure seen only when reading the end of a disc.
■ Columns 4–8. Indicate the actual minimum “x” speed for CAV drives, along with the minimum
transfer speed (when reading the start of any disc) and an optimistic average speed (true only
when reading a full disc; otherwise, it’s even lower) in both “x” and byte-per-second formats.
■ Columns 9 and 10. Indicate the maximum linear speeds the drive attains, in both meters per second
and miles per hour. CLV drives maintain those speeds everywhere on the disc, whereas CAV
drives reach those speeds only on the outer part of a disc.
■ Columns 11 and 12. Indicate the rotational speeds of a drive. The first of those shows how
quickly the disc spins when reading the start of a disc. This applies to either CAV or CLV drives.
For CAV drives, that figure is constant no matter where on the disc is being read. The second of
those two colums shows the maximum rotational speed if the drive were a CLV type. Because
most faster drives are CAV, those figures are mostly theoretical for the faster drives.
■ Column 13. Shows the speed the drive would be rated if it were a CD-ROM drive. This is based
on the rotational speed, not the transfer rate. In other words, a 12x DVD drive would perform
as a 32x CD-ROM drive when reading CDs. Most DVD drives list their speeds when reading CDs
in the specifications. Due to the use of PCAV (Partial CAV) designs, some might have higher CD
performances than the table indicates.
DVD Formats and Standards
As with the CD standards, the DVD standards are published in reference books produced mainly by
the DVD forum, but also by other companies.
The DVD-Video and DVD-ROM standards are pretty well established, but recordable DVD technology
is still evolving. The standards situation for recordable DVD is more confusing than usual, especially
because there are at least four different (and somewhat incompatible) recording formats! It remains to
be seen which will have the best support and become the most popular, but so far the DVD+RW format
looks to be the most promising.
The current standard DVD formats are shown in Table 13.21.
Table 13.21 Standard DVD Formats and Capacities
Data Video
Format Disc Size Sides Layers Capacity Capacity
DVD-ROM Formats and Capacities
DVD-5 120mm Single Single 4.7GB 2.2 hours
DVD-9 120mm Single Double 8.5GB 4.0 hours
DVD-10 120mm Double Single 9.4GB 4.4 hours
DVD-14 120mm Double Both 13.2GB 6.3 hours
DVD-18 120mm Double Double 17.1GB 8.1 hours
DVD-1 80mm Single Single 1.5GB 0.7 hours
DVD-2 80mm Single Double 2.7GB 1.3 hours