Computer Parts-Optical Disc

CD-ROM (Compact Disk Read Only Memory)

It is a storage device with medium capacity i.e. to hold 650 MB/700 MB (60/80 Min. Audio/Video). Computer has special drive known as CD-Drive to provide support for placing and running CDs. It can store data, audio and video.

It is made up of plastic with special surface having optical sensitivity. CD-Drive has a laser light source that reads data from the CD-ROM. The CD-ROM surface is a mirror covered with billions of tiny bumps that are arranged in a long, tightly wound spiral track of data, circling from the inside of the disc to the outside.

The CD-Drive reads the bumps with a precise laser and interprets the information as bits of data. CD-ROMs are economical and easily available storage media. CDs are available in variations such as CD-R (Compact Disk Recordable) and CD-RW(Compact Disk Rewritable).

The data on CD-R media can only be written once whereas CD-RW media allows multiple write/over-write operations on it. There are two types of CD Drives, one known as CD-R Drive that performs only read operation, and the other known as CD-RW Drive (or CD-Burner) that performs read as well write operations.

Working of a CD-ROM Drive

When you play a CD, the laser beam passes through the CD's polycarbonate layer, reflects off the aluminum layer and hits an optoelectronic device that detects changes in light. The bumps reflect light differently than the flat parts of the aluminum layer, which are called lands. The optoelectronic sensor detects these changes in reflectivity, and the electronics in the CD-player drive interpret the changes as data bits.

DVD (Digital Versatile Disc)

Computer has special drive known as DVD-Drive to provide support for placing and running DVDs. A DVD is very similar to a CD, but it has a much larger data storage capacity. A standard DVD media holds about seven times more data than a CD media.

This huge capacity means that a DVD has enough room to store a full-length, MPEG- 2-encoded movie, as well as other information. A DVD can store data, audio and video. It is made up of plastic with special surface having optical sensitivity denser as compared to CDs. A DVD drive is capable of running a CD media also.

The DVD media can store up to 4.7 GB of data as compared to 650-700 MB storage capacity of CD-ROMs. DVDs are of the same diameter and thickness as CDs, and they are made using some of the same materials and manufacturing methods. Like a CD, the data on a DVD is encoded in the form of small pits and bumps in the track of the disc.

Pen Drive

This is a type of flash memory storage device of the size of a thumb and can plug into the USB port of the computer. USB flash drives are more compact, generally faster, hold more data, and are more reliable (due to their lack of moving parts) than disk storage.

Most flash drives use a standard USB connector, which is connected directly to the USB port on a personal computer. Flash drive is nearly free from scratch and dust problems that exist in the other storage media, such as floppy disks and compact discs.

This makes it ideal for transporting data or work files from one location to another, such as from home to school or office or work places. It also allows one to perform multiple read-write operations. Flash drives are also a relatively dense form of storage, where even the cheapest will store dozens of floppy disks worth of data.

Some can hold more data than a CD (700 MB). Top of the line flash drives can store more data than a DVD. Flash drives often last for 500,000 or more erase/write cycles. Optical storage devices are also slower than their flash-based counterparts.


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