Introduction
Over the last several decades, there has been a meteoric rise in the capacity of computer systems to store various types of media. Memory storage technologies have gone a long way from the days of floppy discs, moving on to CDs and DVDs, then USBs, and finally arriving at SSDs and HDDs. Because of advancements in computer technology, it is now feasible to store vast amounts of data on very compact devices, which only need a small fraction of the space that was previously required.
The compact disc (CD) and the digital versatile disc (DVD) are both types of an optical discs, with the primary distinctions being size and production process. In general, a DVD is capable of storing more data than a CD. One of the reasons for this is because CDs only have the polycarbonate substrate on one side, but DVDs have it on both sides. In our prior post on the differences between magnetic discs and optical discs, we went over the components that make up an optical disc as well as the operating principle behind how it reads and writes data.
CDs and DVDs both use optical technology, which involves retrieving data via the use of light, and more especially, lasers. To read the information (data) that is contained in the disc in the form of bits and to write the content, a laser beam is focussed into the CD or DVD.
CD vs DVD
The primary difference between a compact disc (CD) and a digital versatile disc (DVD) is that although both are constructed from the same types of materials, DVDs have two reflective layers, whilst CDs only have one. This extra layer enables DVDs to hold far more data than CDs. The fact that a DVD can store more information than a CD can give it a distinct advantage in terms of both storage capacity and performance.
A compact disc, sometimes known as a CD, is a kind of optical disc that can hold various amounts of data. A typical compact disc has a storage capacity of 700 megabytes, and each byte is comprised of 14 bits. The data is typically stored on the first layer of a CD, which is made of polycarbonate plastic and is the layer's construction material. The information is stored in depressions that have been made on the surface of the polycarbonate.
The Digital Versatile Disc, or DVD, was developed as a means of storing digital information without compromising the integrity of the data during storage. Because digital data is often quite large, there was a need for a storing method that was more efficient. A standard DVD can contain seven times as much information as a CD.
The introduction of the compact disc (CD), which stands for "compact disc," was the first step toward the concept of digitally encoding information. It makes use of an innovative coding approach in which a code consisting of 14 bits is used to signify a computer memory unit, and this style of coding also contributes to the process of error detection. It had been a suitable alternative for the memory device since it supplied a low-cost solution for storing a large amount of information. This was the primary reason why it had been accepted.
DVD, which stands for Digital Versatile Disk, is an alternative to videotape, which is used in tape recorders (Video container Recorders), and fixed storage, which is used in computers. This is because videodiscs can acquire seven times the amount of information that can be stored on CDs. It generates films with excellent visual quality and provides random access to the frames. A videodisc is created from the same material as a compact disc (CD), but the process and thus the layers are fundamentally different. A videodisc is utilized from each of the edges, similar to how 2 CDs are projected along. The error-correcting codes used in DVDs are RS-PC and EFMplus respectively.
Difference Between CD and DVD in Tabular Form
| Parameters of Comparison | CD | DVD |
| Definition | A compact disc, sometimes known as a CD, is a kind of optical disc that can hold a certain amount of data. | A digital versatile data disc, sometimes known as a DVD, is a kind of optical disc that is used only for the purpose of storing digital or video data. |
| Storage capacity | CDs have a storage capacity of 700 megabytes. | The average DVD has the capacity to contain anything from 4.7 to 17 GB of data. |
| Storage layers | CDs only have a single layer of storage behind them. | DVDs include two separate levels of data storage. |
| Metal layer position | The recording layer, which is made of metal, is placed on top of the disc. | The recording layer, which is made of metal, is located in the centre of the disc. |
| Spacing between recording pits | Pits are separated from one another by 0.834 micrometres in total distance. | A distance of 0.4 micrometres separates each pit in the surface. |
What is CD?
The term "compact disc" (CD) refers to a specific kind of optical disc that may be used to store various types of data. A standard compact disc has a storage capacity of 700 megabytes, where one byte is comprised of 14 bits. CDs employ laser light to retrieve data. The information is kept in the polycarbonate layer, which is the first layer of a compact disc (CD). Pits, which are employed for data storage, are recessed throughout the layer.
A distance of 0.834 micrometers separates each pit. The information is etched into the pits using a laser light that has a high intensity. The recording layer is shielded from damage by a thin layer of aluminum, which is followed by an additional shield of protection in the form of a thin layer of acrylic. As a result, of there only being one reflective layer in a CD, there is only one layer of storage space accessible on a CD. Laser light is focused on the pits that are located on the polycarbonate layer of a CD to read the bits that are stored there. A photodetector located inside the CD player reads the pits because they reflect some of the light that is passing through them.
The part of the light that was detected is then interpreted by the integrated circuit that is included inside the CD player, and the result is read as bits of data. The storage capacity of a CD is very constrained because there is only one layer of polycarbonate in the CD. As a result, CDs have gradually lost their relevance over the years.
The first step toward the concept of digitally encoding the data was taken with the introduction of the compact disc, sometimes known as a CD. It employs a one-of-a-kind way of encoding, in which each byte is represented by a 14-bit code, and this form of encoding also contributes to the process of error detection. As a result of its ability to store a considerable quantity of information at a cheap cost, it was an excellent candidate to take the role of magnetic discs.
The indentation pits in the polycarbonate material that makes up the first layer of a CD serve to store the information that is written to it. This layer also serves as the basis of the transparent glass. The term "land" refers to any region that is level or featureless. The programmable disc is covered with the thin material made of aluminum, and then a protective acrylic coating is applied on top of the aluminum layer. The last step involves a label pressing a stamp into the disc. The pits are organized into the spiral track, in the outward direction from the center of the disc. However, the danger of damage is decreased by storing the index information at the beginning of the disc. The length of the pit is 0.8-3 microns, and the width of the pit is 0.5 microns.
The bits that have been stored are read by directing the laser light onto the portion of the spinning disc that is made of polycarbonate. The light that is detected by the photodetector is reflected by the section of the disc that has been indented. The compact disc comes in a few different iterations, the most common of which are the CD-R, CD-ROM, and CD-RW.
What is DVD?
Digital Versatile Disc (DVD) is an optical disc used primarily to hold digital or video data. As a result of the fact that video data often include a huge number of data bytes, the storage capacity of DVDs is also typically rather considerable. The amount of data that may be stored on a standard DVD can vary anywhere from 4.7 to 17 gigabytes. This is because of the way that the DVD was put together. A DVD is constructed using the same components as a CD; however, it has two times the number of layers that a CD has.
The information that makes up a DVD is written onto a layer made of polycarbonate. A compact disc (CD) only has a single layer of polycarbonate in it. Because of this, the amount of data that can be stored on a CD is very restricted. On the other hand, a DVD consists of two layers of polycarbonate in its construction. Because a DVD has two reflecting layers, it provides double with the amount of storage capacity as compared to a standard optical disc. On the surface of the polycarbonate DVD, the data are carved into pits that have been recessed into the material.
The pits on a DVD are packed in much more tightly together. On a DVD, there is a space of 0.4 micrometers between any two pits that are directly next to one another. Because pits on a DVD are packed so closely together, it is possible to store more bits, which results in the DVD having a greater capacity for data storage. Because of this, using a DVD to store digital data in a way that is both more efficient and effective than using a CD.
As a replacement for videotape, which is used in VCRs (Video Cassette Recorders), and CD-ROM, which is used in personal computers (PCs), the introduction of DVDs (Digital Versatile Disks) made this possible. DVDs can acquire a seven times bigger quantity of data than CDs can. Videos may be shown with high visual quality and random access thanks to it. A DVD is constructed from the same substance as a CD, but the procedure and the layers are different. A DVD may be used from both sides, similar to how two CDs can be stuck together. It employs a variety of strategies for error correction, including RS-PC and the recording code EFMPlus, among others.
The employment of a laser with a shorter wavelength, more densely packed data, and the creation of two-sided discs are the three factors that contribute to its larger capacity compared to that of a CD (data can be read from written to both the sides). The employment of a laser with a short wavelength is required to get the narrower gap of about 0.74 microns between the spiral tracks and the minimum distance of 0.4 microns between the pits.
In addition to this, it utilizes a dual-layer of pits and lands on the normal layer, as well as a semi-reflective layer on the reflective layer's very top. To read the material of each layer in a DVD independently, the laser has to have its focus adjusted very precisely. DVDs, like CDs, come in a variety of formats, including DVD-R, DVD-RW, and more besides.
Main Differences Between CD and DVD in Points
- The abbreviation for "Compact Disc" is "CD." It is a kind of optical disc that is used for data storage. DVD is an acronym that stands for "Digitally Versatile Disc," and it refers to a kind of optical storage medium that is used particularly to store digital or video data.
- A CD has a storage capacity of 700 megabytes (MB). The amount of data that may be stored on a DVD can vary anywhere from 4.7 GB to 17 GB.
- A compact disc (CD) only has one layer of polycarbonate material. A DVD is composed of two layers of polycarbonate material.
- The layer of metal that is utilized for recording purposes is located at the very top of a CD. The center of a DVD has the metal layer that is used for recording. This layer is positioned in the center of the disc.
- The distance of 0.834 micrometers that exists between each pit on a CD is what allows for the recording of data on the medium. The distance between each pit on a DVD is 0.4 micrometer.
- In comparison, the data transmission rate for DVDs is 11 Mb/sec, while the data transfer rate for CDs ranges from 1.4 to 1.6 Mb/sec.
- The bit length of a channel on a CD is measured at 300 nanometers, while the bit length of a channel on a DVD is measured at 113 nanometers.
- It is possible that removing the adhesive label off a CD can cause the disc to become severely damaged. The spin, on the other hand, will become uneven after the adhesive label on the DVD has been removed.
Conclusion
The use of the floppy disc to store bits of data was superseded by a superior alternative made possible by the development of the optical disc as a medium for data storage. Optical discs had a greater storage capacity but took up a less amount of area than other data storage mediums did physically. CDs and DVDs are the two kinds of optical discs that get the most used daily. Companies such as Sony and Phillips were the first to develop compact discs.
CDs were a convenient and speedy way to store data on computers because of their small size. DVDs and CDs both employ the same basic idea of storing data, however, DVDs provide far greater capacity and are significantly more efficient than CDs.
Because DVDs provided a more efficient and effective means of storing data than CDs did, CDs eventually became obsolete with the introduction of DVDs.
Both the CD and the DVD are examples of optical recording mediums; however, the CD was designed specifically as an audio storage format, while the DVD is a general storage format. The more recent technology of DVD can store almost seven times as much data as a CD, and its format efficiency is also thirty-two percent higher than that of a CD.
References
- https://www.aes.org/e-lib/online/browse.cfm?elib=12144
- https://www.google.com/books?hl=en&lr=&id=BGnxDwAAQBAJ&oi=fnd&pg=PR9&dq=compact+disc&ots=36ebh0vDhz&sig=MK0tsVuMoSNZYf9C_xlZQe4eBFE
- https://ieeexplore.ieee.org/abstract/document/7243464/
- https://iopscience.iop.org/article/10.1143/JJAP.37.2257/meta
