There are a huge range of options today for storing data. From a simple USB pen drive to external hard drives, cloud storage and optical media like CDs and DVDs. When you're considering personal storage needs, it helps to know how much each type of storage device can hold. In general, CD capacity is 700 MB, whereas DVD storage capacity is 4.7 GB. But to be sure you make the right decision, take time to learn more.
CD stands for compact disc, and compared to storage methods that came before it like floppy discs, vinyl records (for music specifically) and cassette tapes, it offered a wide range of advantages. As well as not needing to be rewound after it had finished playing (like cassette tapes) and making it easier to skip to the next track on a music CD (offering an advantage over vinyl records), the improvement in storage space was a huge benefit. The average CD capacity is 700 MB.
This storage space might not mean too much to you in terms of megabytes, so you can think of it in terms of the amount of audio and video you can store on the disc. For CD-quality audio, a CD can store about 80 minutes of content, whereas for videos you can get around 60 minutes of content onto the disc. The size of picture depends strongly on the resolution and physical size of the image, but generally speaking, an average picture can be considered anywhere from 4 to 24 MB. At 10 MB per picture (roughly the size of a 15 megapixel high-quality JPEG image), you can store about 70 pictures on a single CD.
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DVD Storage Capacity
DVD stands for Digital Versatile Disc, and they have quickly become the preferred storage type for many different applications. In particular, movies are commonly stored on DVDs, but they're also being used much more often for things like computer programs and other types of data.
An average DVD storage capacity is 4.7 GB, which is over six and a half times the size of a CD. This is enough to store 120 minutes of high quality video (or 180 minutes of standard definition video), which explains why movies weren't commonly stored on discs until DVDs became widely available. Although audio storage on DVDs isn't particularly common, you could fit about six hours of CD-quality audio on a DVD, or if you're using MP3s, a whopping 72 hours. Using the same size of image as before (10 MB per picture), a DVD can store 470 images.
There are also other types of DVD – including dual-layer discs or double-sided discs – which increase the storage size substantially. A dual-layer disc stores around 8.5 GB of data, while a double-sided disc stores 9.4 GB.
CD vs. DVD: The Differences
Both CDs and DVDs are small discs and look essentially the same. However, there are many differences between the different technologies when you dig a little deeper. The biggest difference is the one addressed above: DVDs have much more storage space than a CD, making them perfect for things like fitting full movies on a single disc. DVDs also have more options when it comes to multiple layers and being double-sided.
The reason DVDs can hold more data than CDs is related to how closely-packed the information is on the readable surface of the disk. In both cases, the data is stored in collections of "dots," very shallow pits on the surface of the disk, read by the laser in the player and basically translated into a series of 1s and 0s to produce audio, video or other data. On a DVD, the dots are much more compactly-stored and much smaller in size than they are on a CD, which translates into a greatly-increased storage capacity.
This also explains another important difference between CDs and DVDs. You can play CDs on a DVD player, but you can't play DVDs on a CD player. This is because the laser on a DVD player has to be capable of reading the tinier dots on the surface of the disc (by using smaller-wavelength light), whereas the laser on a CD player doesn't need to be as precise. So the technology used to read DVDs can easily interpret the relatively sparse pattern of dots on a CD, but a CD reader simply can't be precise enough to read the data from a DVD.
When Did DVDs Come Out?
DVDs were invented in 1995, with Sony, Phillips, Toshiba and Warner Home Entertainment all working on projects to produce something like the technology we know today. Sony demonstrated its DVD technology in January of that year, but three weeks later Warner and Toshiba announced their alternative form of the technology, which was double-sided and thinner than Sony's and Phillips' version. A debate erupted in the technology industry about which approach was better, and more companies joined the development of the technology.
The standardized DVD wasn't in development until technology giants Apple, Compaq, IBM, Microsoft, HP and Fujitsu released a report stating they refused to support either form of the DVD while there were two distinct types trying to be brought to market. This resulted in the companies coming together – and using elements of both existing designs – to settle on a "standard" for the DVD. By 1996, the first feature films were released on DVD, while commercial DVD players hit the United States market in 1997.
Types of DVDs
There are many different formats of DVD on the market, and to really understand the technology you need a working understanding of what these are. The simplest type is a DVD-ROM, where "ROM" stands for "read only media," meaning that the content is written onto the disc prior to being sold and can't be rewritten. The first form of writable DVD drive, called DVD-RAM, was first sold in 1998, but despite being a good idea in principle, it never really made headway in the field as a whole.
DVD-R (recordable) was the first format of DVDs released that was write-once, and they're still available today, compatible with around 90 percent of DVD players on the market. However, the error correction and detection on these discs is worse than the similar format DVD+R, and this other format is also compatible with the vast majority of DVD players on the market, although only around 85 percent. There is also a dual-layer version of DVD+R, called DVD+R DL, with a greater storage capacity of 8.5 GB, as well as the same thing for DVD-R.
DVD-RW is a rewritable DVD format, which allows you to rewrite the information on the disc up to 1,000 times. However, like DVD-R, the error correction and detection mechanism on these discs aren't as good as the plus format. This means the DVD+RW format is technically better, and both formats are now around the same price, so there's little benefit in choosing DVD-RW. The +RW format is also capable of being read by slightly more DVD players, although both are compatible with roughly 70 percent of players on the market.
Types of CDs
The types of CDs available closely follows the types of DVDs, with a CD-ROM standing for compact disc-read only media and being the simplest format. The CD-R format can be written onto only once, but these discs are compatible with pretty much any CD player or CD drive you'll find today. Technically, these discs should have a smaller capacity of 650 MB, but most modern discs have the standard CD capacity of 700 MB.
CD-RW (rewritable) discs can be written onto and rewritten onto up to 1,000 times, much like the DVD-RW discs. While most CD writing drives will burn onto CD-R discs at the maximum speed possible for the drive, CD-RW discs have stricter limits on writing speed, so the drives base their speed on the capabilities of the disc. Standard CD-RW discs can be written onto at up to 4X speed, while high-speed versions support up to 12X, ultra-speed versions support up to 24X and ultra-speed-plus discs support burning at up to 32X.
Blu-Ray and HD DVD Discs
CDs and DVDs aren't the only types of optical storage discs available today, with Blu-Ray and HD DVD discs having extra capacity to support HD-quality video files. Compared to the 4.7 to 9.4 GB capacity of a DVD, an HD DVD has 15 GB of storage space for a single-layer disc and 30 GB for a dual-layer disc.
Comparatively, Blu-Ray is better when it comes to storage capacity, offering 25 GB in single-layer formats and 50 GB in dual-layer formats. The two technologies were engaged in a format war as both of the technologies were released, but despite the cheaper cost of HD DVD discs, Blu-Ray's additional storage space, and the wider support for the format, settled the issue. Blu-Ray discs and players remain common, but HD DVDs are not so widely-used and are likely to become obsolete in the same way as Betamax did after losing out to VHS.
Alternatives for Storage
For many years, optical media had a definite advantage when it came to storing files, music and video clips. However, there are now a huge range of options available for storage which blow even the dual-layer DVD storage capacity out of the water. The alternative storage options available are also generally easier to use and support rewriting of data in a much more intuitive way.
The most well-known alternative storage devices are USB pen drives or sticks. These are very affordable and tend to be able to store huge amounts of data, with sticks of 128 GB of storage space being very common and others offering up to 512 GB or even more. There is no competition if you're looking at raw storage space and the flexibility of the medium, with essentially any device with a USB port able to read the information. If you want something even bigger, external hard drives work in a similar way, but have much larger capacities, in the terabyte (TB) range.
SD cards are another storage medium that can be read by a huge range of devices. While SD card readers aren't as common as USB drives, SD cards can store huge amounts of data, again surpassing what optical media are capable of. For example, SD cards with 128 GB capacities are common, and some modern cards even approach 1 TB or more.