Explain the working of CD-ROM and DVD-ROM
A Compact disc read-only memory (CD-ROM) is a storage device that can be read but not written to.
CD-ROM was a common convention for delivery of audio and other data through the years before small solid-state flash drives and other devices began to take over.
Techopedia Explains Compact Disc-Read-Only Memory
As magnetic tape had replaced vinyl, the compact disc replaced magnetic tape as a durable, easy way to store information.
In many ways, the CD-ROM was the last physical data storage method, coinciding with the use of floppy disks for computers. By contrast, today’s data storage and data transmissions are mostly ‘completely digital’ in the sense that tiny pieces of hardware can handle the information that would have been put in dozens of individual compact discs or floppy disks.
As compact discs became a common data format for both music and other kinds of data, writable CDs allow users to download data from their computers to be used in other devices, for instance, in replicating songs and playlists for use in stereo systems with compact disc capability.
As compact discs became useful for storing and delivering software in addition tomusic, companies worked on specific technical protocols for different kinds of digital data written onto CD-ROM products. These continue to help manage video, individual files and different kinds of data that may be on a compact disc.
Digital versatile disc-read only memory (DVD-ROM) is a read-only digital versatile disc (DVD) commonly used for storing large software applications. It is similar to a compact disk-read only memory (CD-ROM) but has a larger capacity. A DVD-ROM stores around 4.38 GB of data. A CD-ROM usually stores 650 MB of data.
A DVD-ROM permanently stores data files which cannot be changed, written over or erased. A personal computer (PC) with a DVD-ROM or a DVD-RAM drive is designed to read a DVD-ROM disc. Generally a DVD-ROM disc is not equipped to be used with a DVD drive connected to a home theater system or television. But many DVD-ROM drives can generally read a DVD movie disc.
A DVD-ROM is one of the various types of DVDs. A blank DVD is generally a DVD-R or DVD+R, which has a read-write format. The +R or -R references the format standards and is a rewritable or recordable DVD.
Compared to a CD-ROM, a DVD-ROM has the same 5 inch diameter and 1.2
millimeter (mm) thickness. But because a DVD-ROM uses a shorter wavelength laser with tighter compacted pits, the disc capacity is increased. In fact, the smallest DVD-ROM can store approximately 7 times more data than a CD-ROM.
This term is also known as digital video disc ROM.
Techopedia Explains Digital Versatile Disc-Read Only Memory
The DVD-ROM was first introduced in 1996 by the DVD Forum, a group of ten international companies using and developing DVD and HD DVD formats for media, software and hardware. The DVD Forum consists of the founding companies plus over 220 other members. Japan produced the first DVD-ROMs in November 1996. By March 1997 it was introduced in the United States. The DVD Forum also releases all DVD specifications published in the DVD books by titles such as DVD-ROM Book or DVD-R Book.
A typical DVD-ROM can hold up to 17 GB/s of data if both sides of the disc are writable.
The DVD-ROM is comprised of two 0.6 millimeters (mm) acrylic layers bondedtogether. The double-sided disc consists of two recordable grooved sides. With two layers, a DVD’s laser beam only has to go through 0.06 mm to reach the recording layer. Having a thin layer allows the lens to focus the beam to a smaller spot size, which in turn writes smaller pits for more data. The data is encoded in the form of spiral pits that are merely nanometers apart. The spiral path begins at the center of the disc and coils numerous times until it reaches the outer edge. With a double-layered disc the path continues to the second layer. A double-sided disc needs to be manually turned over and the path resumes in the center.