Optical Devices
Click on an Issue below to jump or scroll down to read the entire article.
- What is a CD-ROM?
- What is a CD-ROM drive?
- What is ATA/IDE?
- What is EIDE?
- What is ATAPI?
- Define data transfer rate.
- Define access time.
- What is digital servo?
- How do you measure CD-ROM drive performance?
- How does a drive's speed affect its
performance?
- What is DVD?
- What are the advantages of DVD-ROM over
CD-ROM?
- What is a CD-R/RW drive?
What is a CD-ROM?
CD-ROM is short for Compact Disc-Read Only Memory, which is a type of optical
disk capable of storing large amounts of data – up to 680MB per disc. A single
CD-ROM has the storage capacity of 470 floppy disks, enough memory to store
about 340,000 pages of text.
CD-ROMs require a special machine to record the data, and once recorded, they
cannot be erased and filled with new data. To read a CD, you need a CD-ROM
drive. Almost all CD-ROMs conform to a standard size and format, so it is
usually possible to load any type of CD into any ROM drive. In addition, most
CD-ROM drives are capable of playing audio CDs, which share the same technology.
CD-ROMs are particularly well suited to information that requires large
storage capacity. This includes color graphics, sound, and especially video. In
recent years, as the prices of CD-ROM drives have decreased, the tools for
creating new CD-ROM titles have improved, and the CD-ROM industry has been
expanding rapidly. To date, the most popular CD-ROM titles have been computer
games and multimedia reference works.
What is a CD-ROM drive?
A CD-ROM drive is a device that can read information from a Compact disc.
CD-ROM drives can be either internal, in which case they fit in a drive bay, or
external, in which case they are usually connected to the computer’s parallel
port or SCSI port. Parallel CD-ROM drives are easier to install, but they have
several disadvantages. They are somewhat more expensive than internal drives;
they use up the parallel port, which means that you can’t use that port for
another device such as a printer; and the parallel port itself may not be fast
enough to handle all the data pouring through it. SCSI CD-ROM needs an extra
SCSI controller board to have it connected. Typically, SCSI controller boards
are more expensive than IDE ports.
There are a number of features that CD-ROM classifies drives, the most
important of which is the speed. CD-ROM drives are generally classified as
single-speed, double-speed (2X), triple-speed (3X), quadruple-speed (4X),
hex-speed (6X) or odo-speed (8X), deca-speed (10X), or triple quad-speed (12X).
Within these groups, however, there is some variation. Two more precise
measurements are the drive’s access time and data transfer rate. The seek time,
also called the access time, measures how long, on average, it takes the drive
to access a particular piece of information of disc. The data transfer rate
measures how much data can be read and sent to the computer in a second.
Aside from speed, another feature which CD-ROM classifies drives is
compatibility with existing standards. If you plan to run CD-ROMs in a Windows®
environment, you need a drive that conforms to MPC II standard. If you want to
view photographs stored on CD-ROM, make sure your drive conforms to the format
of a Kodak PhotoCD.
Finally, you should consider how the drive connects to your computer. Most
CD-ROMs connect via a SCSI bus. If your computer does not already contain such
an interface, you will need to install one. Other CD-ROMs connect to an IDE or
Enhanced IDE interface, which is usually the interface used by the hard disk
drive.
What is ATA/IDE?
ATA (Advanced Technology Attachment) and IDE (Integrated Drive Electronics)
both refer to disk drive designs that integrate the controller into the drive to
reduce the interface cost and to ease firmware implementation.
What is EIDE?
EIDE, short for Enhanced IDE, is a new version of the IDE mass storage device
interface standard developed by Western Digital Corporation. It supports
transfer rates of between 11.1 and 13.3 megabytes per second, about three to
four times faster than the old IDE standard. In addition, it can support mass
storage devices of up to 8.4 gigabytes per device, whereas the old standard was
limited to 528MB. Because of its lower cost, enhanced IDE is expected to replace
SCSI in many areas.
What is ATAPI?
AT Attachment Packet Interface (ATAPI) is a standard for devices such as
CD-ROM drives and tape drives, which specifies an interface that is compatible
with ordinary ATA (IDE) port. The advantages of using ATAPI hardware are low
cost and compatibility with an installed IDE adapter.
Define data transfer rate.
Data transfer rate is the speed with which data can be transmitted from one
device to another. Data rates are often measured in megabits (million bits) or
megabytes (million bytes) per second.
Define access time.
Access time is the time a program or device takes to locate a single piece of
information and make it available to the computer for processing. The access
time for disk drives refers to the time it actually takes for the read/write
head to locate a sector on the disk. This is an average time since it depends on
how far away the head is from the desired data. Disk access times are measured
in milliseconds (thousandths of a second); often abbreviated as ms. A drive with
lower access time indicates that it is a higher performance model.
What is digital servo?
This function automatically adjusts the gain/offset to ensure data reading
accuracy and reliability. In contrast to the analog servo, which needs manual
adjustment in the factory prior to its shipment, the digital servo requires no
adjustment during manufacturing, guaranteeing high quality (complies with ISO
9001) and lower costs.
How do you measure CD-ROM drive performance?
The performance of a CD-ROM drive is dependent on two factors: data transfer
rate and access time. Data transfer rate refers to the amount of data that a
CD-ROM drive can send to a PC in a certain period of time. For example, a CD-ROM
with 900 KB/sec transfer rate can read 900k (921,600) bytes of data and transmit
it to a PC in one second. (Note that the transfer rate might alter depending on
the power of the PC system.) Access time is the time required for a CD-ROM drive
to find the desired data on a disc. A shorter access time indicates better
performance. When talking about access time, the term "one third stroke" is
often used. Stroke refers to the distance from the innermost track to the outer
most track of a CD-ROM disk. One-third stroke access time is the time it takes
for a laser pickup to read data by moving 1/3 stroke over the CD-ROM disk.
How does a drive’s speed affect its performance?
A CD-ROM’s speed is measured in terms of its data transfers rate. The data
transfer rate for a CD-ROM drive is measured in terms of bytes per second and
measures the speed at which the drive can transmit data to the system’s memory
and CPU for processing. The higher the data transfer rate and the shorter the
access time, the better the performance of a drive.
Older single speed drives could transfer data at 150K bytes/second, the same
speed as a standard audio drive; but at this speed, images were jumpy and sound
output had pops and cracks in it when the drive was used to read a video file
such as a Video-CD clip. New multi-speed drives (20X, 24X, 32X) significantly
improve a system’s performance when handling image files. Today’s PCs can handle
more in the way of live video clips and animation, and Windows® 95 offers direct
support for multimedia; however, to take advantage of these new developments you
should use a high-performance multi-speed drive like AOpen’s 20X, 24X and 32X
speed drive, model CD-920E/CD-924E/CD932E.
What is DVD?
DVD, short for Digital Versatile Disk, is the newest standard for optical
storage, which specifies a disk that is the same size as a standard CD but is
able to hold much more information. An industry consortium of electronics
companies led developed DVD by Toshiba® and Philips®, and it is anticipated the
new standard will usher in a new era of growth for multimedia, interactive
applications on the PC.
For PC applications, DVD will be used the same way the CD-ROM is used today.
The main attraction for PC users is the larger capacity of the DVD disk. The
capacity will be 17gig on a double-sided dual layer disk, 8 gig on a single
sided dual layer, and 8.4 gig on a CD-R which only be single layer but could be
double or single sided. The PC will also be able to play DVD-Audio and
DVD-Video; two standards developed primarily for home electronics devices. New
ROM drives, called DVD-ROM, will be arriving on the market to accommodate the
new disk format.
Advances in digital video and audio standards are coinciding with the
development of the DVD to create unprecedented multimedia storage capacities.
For instance, MPEG-2 video and audio compression will be used to compress still
images such as scanned or pictures as well as full motion video. This
compression will allow much greater storage than you could attain using a hard
drive; for instance, a single-layer, single-sided DVD has enough capacity to
hold two hours and 13 minutes of video. Some DVD-ROM drives will have a built-in
MPEG-2 chip, and some others will use an MPEG-2 chip installed in the PC.
What are the advantages of DVD-ROM over CD-ROM?
DVD-ROM drives offer several advantages over CD-ROM drives, especially in the
area of storage capacity:
Greater Capacity: With 4.7 gigabytes of storage capacity on a single
layer and 8.4 gigabytes on a dual-layer disc, DVD-ROM offers more than 12 times
the capacity of CD-ROM. When information is stored on both sides of the disk a
single disk can hold up to 17 gigabytes, which is equal to 26 CD-ROM or 12,000
floppies.
Faster data transfer: A basic DVD-ROM drive offers variable data transfer
rate at an average rate of 1,108 kilobytes per second.
Flexibility: DVD will allow greater use and flexibility of Data
Warehousing than ever before possible. One manufacturer has already developed a
100-disk jukebox for DVD that can store 800 gig of data in a box only 2’x2’.
Better Video: Because DVD-ROM has greater storage capacity and a faster
data transfer rate than CD-ROM, it is possible to deliver up to full length
movies on a one-sided disk using compression/decompression that yields broadcast
quality video and stereo sound tracks for use in MS-DOS®/Windows® 3.x. Other
operating systems supply their own ATAPI CD-ROM device drivers.
What is a CD-R/RW drive?
CD-RW is a rewriteable CD utilizing an innovative phase change recording
material (Ag-In-Sb-Te). This breakthrough effectively increases data
eraseability and recording sensibility, which are two major drawbacks of
conventional phase change recording material. During the write operation to a
CD-RW, recording switches between the "amorphous" phase (recorded state) with
lower reflectivity and the "crystal" phase (erased state) with higher
reflectivity according to the temperature rising/falling through laser beam
irradiation.
The CD-RW is ideal for personal uses, such as data back up and making
original CDs, because it allows users to overwrite repeatedly. With CD-R, user
can make discs for distribution, create electronic albums of digital camera
images, store data that should not be revised or deleted.
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