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Faculty of Nursing
Adult care Nursing Department
underneath the other. Finally, a different manufacturing technique allows the use of both sides of a DVD.
Each layer on a DVD can hold approximately 4.7 GB. If both layers on both sides are used, the DVD
capacity is approximately 17 GB. The use of a blue laser extends this capability even further, to
approximately 50 GB. WORM, or write-once-read-many-times, disks were originally designed to provide
an inexpensive way for archiving data. WORM disks provide high-capacity storage with the convenience
of compact size, reasonable cost, and removability. As the name indicates, WORM disks can be written,
but, once written, a data block cannot be rewritten. The inability to tamper with the data on a WORM
disk has taken on importance in business, where the permanence of many business data archives is
required for legal purposes. When a file is updated, it is simply written again to a new block and a new
directory entry is provided.
Thus, a complete audit trail exists automatically. When the disk is filled, it is simply stored away and a
new disk used. WORM disks work similarly to a CD or DVD. The major difference is that the disk is made
of a material that can be blistered by a medium-power laser. Initially, the entire disk is smooth. When
data is to be written, the medium-power laser creates tiny blisters in the appropriate locations. These
correspond to the pits in a normal CD-ROM. The WORM disk is read with a separate low-power laser in
the same way as a CD-ROM. This blister technology is used in various CD and DVD formats, called CD-R,
DVD-R, and DVD+R. Additionally, there are rewriteable versions of this technology. These are known as
CD-RW, DVD-RW, DVD+RW, DVD-RAM, and DVD+RAMBD-RE. There are file compatibility issues
between the different WORM and rewriteable CD and DVD formats. Some drives will read every format;
others will only read some of the formats.
Figure 9 CD-ROM Read Process.
70 Academic Year 2025/2026
