NICE PPT

1. B.TECH (MBA) ECE
ROLL NO. :- 34
 REG. NO:- 10808679
 SECTION :- B6803(G2)

2. COMPACT DISK READ ONLY
MEMORY

4.  Compact Disc Read Only Memory.A
compact disc format that is used to
hold text,graphics, and hi-fi stereo
sound.The disc is almost the same as
the music CD,but uses different tracks
for data.The music CD player cannot
play CD-ROM disc but CD-ROM
players may be able to play music CD
discs and have jacks for connection to
an amplifier and/or earphones.A CD-
ROM player is cabled to and
controlled by a card that is plugged
into one of the PCs expansion slots.

5. • Sony of Japan and Philips of the
Netherlands developed the compact disc
(CD), a small hard plastic disc that could
be economically produced in large
quantities. CD-Audio was the first
application for this new technology. CD-
Audio was very successful, due in large
part to the producers adherence to a set
of specifications that later became
standards. The adherence to these
standards lead to the worldwide growth
of the CD-Audio industry. When CD-ROM
was designed, the industry recognized
the need for standards and developed
ISO 9660 as the base standard for all CD-
ROMs.

6. • Physically, the standardPhysically, the standard
compact disc is a disc made ofcompact disc is a disc made of
clear polycarbonate plastic,clear polycarbonate plastic,
coated with a reflective metal,coated with a reflective metal,
and a protective coat of clearand a protective coat of clear
lacquer. Data is placed on thelacquer. Data is placed on the
CD-ROM in the form of smallCD-ROM in the form of small
pits recorded in a spiral trackpits recorded in a spiral track
starting at the center of thestarting at the center of the
CD- ROM and working to theCD- ROM and working to the
outer edge. If the data track ofouter edge. If the data track of
a CD-ROM could be stretcheda CD-ROM could be stretched
out it would be about 4.5Kmout it would be about 4.5Km
long.long.

7.  The standard CD-ROM can hold up to
74 minutes (about 680 Megabytes) of
data, uncompressed. This is roughly
equivalent to 300,000 typewritten
pages. Along with the data, error
detection and correction codes are also
recorded on the disc. This accounts for
the incredibility low error rate when
reading CD-ROMs.

8.  Since CD-ROMs are replicated in large
quantities, the process requires producing a
"master" disc. To produce the glass master, the
encoder's high power laser beam burns the pits
onto a glass disc that has been coated with
photoresist. Once "burned", the glass disc is then
coated with an ultrathin metal coating (usually a
nickel alloy). Finally, it is used to produce the
metal stampers that are fitted into the CD-ROM
replication machines to press the final CD-
ROMs. After stamping the CD-ROMs, they are
coated with the reflective layer (usually
aluminum), the protective lacquer, and finally
the label is printed on it.

9.  Data is read from the CD-ROM with the help ofData is read from the CD-ROM with the help of
CD-ROM drive. While reading a CD-ROM, a lowCD-ROM drive. While reading a CD-ROM, a low
power laser beam is focused on the rotating CD-power laser beam is focused on the rotating CD-
ROM and its reflection is viewed by the readROM and its reflection is viewed by the read
head. When the beam reflects back from the CD-head. When the beam reflects back from the CD-
ROM, it's intensity changes as it moves fromROM, it's intensity changes as it moves from
"land" to "pits". These variations in the laser beam"land" to "pits". These variations in the laser beam
are decoded as data by the CD-ROM drive. Itare decoded as data by the CD-ROM drive. It
should be noted, that unlike hard discs whichshould be noted, that unlike hard discs which
rotate at a constant angular velocity (CAV), CD-rotate at a constant angular velocity (CAV), CD-
ROMs rotate at a constant linear velocity (CLV) ofROMs rotate at a constant linear velocity (CLV) of
about one meter per second. This requires thatabout one meter per second. This requires that
the drives servo mechanism makes the CD-ROMthe drives servo mechanism makes the CD-ROM
turn slower as the read head moves to the outerturn slower as the read head moves to the outer
edge of the disc.edge of the disc.

10.  Data AccessData Access
Unlike tape that must be accessedUnlike tape that must be accessed
sequentially, CD-ROM can be accessedsequentially, CD-ROM can be accessed
randomly. Random access reduces the timerandomly. Random access reduces the time
required to retrieve data. It also allowsrequired to retrieve data. It also allows
retrieval software to quickly retrieve relatedretrieval software to quickly retrieve related
data items across the entire database.data items across the entire database.
 Longevity and IntegrityLongevity and Integrity
Testing suggests that a properly produced CD-Testing suggests that a properly produced CD-
ROM can last more than 100 years. CD- ROMROM can last more than 100 years. CD- ROM
is a read-only medium, which insures theis a read-only medium, which insures the
integrity of the data for the life of the CD-integrity of the data for the life of the CD-
ROM.ROM.

11.  Compared to other storage
disks or diskettes, a CD-
ROM is a very rugged,
long- lasting, secure
medium for storing large
amounts of read-only
information. CD-ROM is
the most cost effective way
to produce and distribute
large quantities of data.