Don't Panic! The world of CD-ROM technology is not as confusing
as your instruction manual.
CD-ROM stands for Compact Disc Read-Only Memory, a mass storage
medium utilizing an optical laser to read microscopic pits on the
aluminized layer of a polycarbonate disc. The same format is used
for audio Compact Discs. Because of its high storage capacity, reliability,
and low cost, CD-ROM has become an increasingly popular storage media.
The storage capacity
of a CD-ROM disc is approximately 650 megabytes, equivalent to
over 500 high density 3.5" floppy disks or roughly
250,000 typed pages.
First generation drives (known as single speed), provided a transfer
rate of approximately 150 kilobytes per second. Hardware manufacturers
then introduced double speed (300 kB/sec), quad speed (600 kB/sec),
and higher. Current drives operate at up to 40 times speed, although
the maximum rate is only achievable over certain portions of the
disc surface.
Most CD-ROM drives use either the Small Computer Systems Interface
(SCSI), ATAPI enhanced IDE interface, or a vendor proprietary interface.
They also typically support playing audio CDs via an external headphone
jack or line level output. Most drives also allow reading the frames
of data from audio CDs in digital form.
CD-ROMs are usually formatted with an ISO-9660 (formerly called
High Sierra) file system. This format restricts filenames to the
MS-DOS style (8+3 characters). The Rock Ridge Extensions use undefined
fields in the ISO-9660 standard to support longer filenames and additional
Unix style information (e.g. file ownership, symbolic links, etc.).
Microsoft has defined a proprietary ISO file system extension called
Joliet which supports long filenames using the 16-bit UNICODE character
encoding.
PhotoCD is a standard developed by Kodak for storing photographic
images as digital data on a CD-ROM. With appropriate software, you
can view the images on a computer, manipulate them, or send them
to a printer. Information can be added to a PhotoCD at a later date;
this is known as multi-session capability.
CD recordable
(CD-R) drives allow writing onto a special "gold" CD
which can then be read by any CD-ROM drive. Data can only be written
once, although using multi-session new data can be appended to a
disc.
CD-RW (rewritable) drives can be erased and rewritten with new data.
They use special discs which can be read by most recent CD-ROM drives
(but not older ones or most audio CD players).
DVD-ROM expands the storage of a CD to as much as 17 gigabytes.
They are commonly used as a medium for distributing full length motion
pictures encoded using the MPEG-2 format. The MPEG video decoding
is performed using specialized decoder software and/or hardware.
DVD-RAM is a writable version of DVD.
