- — 18 October, 2005 11:16
- DVD vs. CD
- Capacity confusion
- Questions to ask yourself
- Comparing DVD standards
- Who supports which standard
- Other Considerations
Comparing DVD standards
As we've seen, the three DVD standards (DVD-RAM, DVD-RW/R, DVD+RW/R) each have their own pros and cons. Below is a breakdown of these standards.
- The name "DVD-RAM" refers to the random method used by this kind of drive to record and retrieve data to and from your discs. True RAM resides in your computer, and parcels out memory to the various programs sitting on your hard drive.
- Although they are optical storage, DVD-RAM discs are treated by a PC as though they are removable hard disks. This means you can drag files DVD-RAM on and off the disc without a dedicated writing (or "burning") process as with other forms of writeable DVD. Files can be added, changed or deleted from the disc without having to rewrite the entire disc.
- Unfortunately, DVD-RAM discs will not function in commercial DVD players, or in the majority of DVD-ROM (computer) drives. DVD-RAM writers won't write to CD-R or CD-RW media either, so you will also need a separate CD burner if you wish to burn CDs. Like all DVD standards, however, DVD-RAM drives can read these CD formats. Note that some DVD-RAM drives can also write to DVD-R discs, which will function in many standard home players.
- The benefit of DVD-RAM discs is that they come in either single-sided or double-sided capacities, providing consumers with even more room for data storage. DVD-RAM discs come in single-sided 2.6GB and 4.7GB discs, as well as double-sided discs which can take up to 9.4GB.
- The biggest difference between DVD-RAM and other DVD standards is that the discs are usually housed in protective caddies. Because the caddies are larger than regular discs, they cannot be slotted into other types of DVD drives or commercial DVD players. Users can take a single-sided DVD-RAM disc out of its caddy, but only the latest generation of DVD-ROM drives will read them. Double-sided DVD-RAM discs are in a sealed caddy and can't be used this way.
- RAM is supported by the DVD Forum, which claims you can rewrite this type of media up to 100,000 times.
- RW stands for rewritable.
- The DVD-RW standard is supported by the DVD Forum.
- Unlike DVD-RAM, DVD-RW writers require their own dedicated writing software (like CD-RW) to be installed on the computer.
- DVD-RW discs do not have a caddy. This means that, physically, DVD-RW discs can fit into any drive and should be readable by most drives, as well as commercial DVD players.
- The standard also supports CD-RW formats, and will write CDs as well as DVDs. This means you don't have to own a CD burner to burn CDs.
- DVD-RW discs are single-sided discs only, and can store up to 4.7GB of data. The DVD Forum claims users can write to the same disc up to 1000 times.
- DVD-RW discs can be read in DVD-ROM drives.
- DVD-R, or DVD-Recordable, is the write-once standard developed for DVD-RW technology and approved by the DVD Forum. The -R discs are the most versatile of DVD media, and can be used with DVD-RW and some DVD-RAM drives.
- DVD-Recordable discs can store up to 4.7GB of data.
- Like CD-R discs, DVD-R discs are single-sided and can only be written to once.
- DVD-R can contain any type of information normally stored on mass-produced DVD discs -- video, audio, images, data files, multimedia programs, and so on.
- The bonus to using DVD-R media is that they are recognised by virtually all DVD-ROM drives and domestic players.
Plus and minus -- much of a muchness?
Talk about rewritable DVD and you'll sound as if you're choking on an acronym salad. The two predominant DVD writing standards -- DVD-RW and DVD+RW -- are often mentioned in the same breath. But does that mean they work the same way? Hardly.
Writing once, writing twice
Each standard formats rewritable discs for packet writing in a different way. The firmware of the +RW standard handles the physical formatting of a disc. When you insert a black disc in the drive, the formatting occurs in the background. During use, it seems as if the drive takes scarcely more than a minute to complete the formatting before it allows you to start copying data to the disc.
DVD-RW leaves disc formatting up to the software you use with the drive. A lot of units supporting DVD-RW include software that formats DVD-RW discs in the background.
DVD-RAM was created with data applications in mind. The discs are preformatted with sector marks when they're made, and manufacturers claim this gives DVD-RAM drives faster random-access capability (like that of hard disks), enabling them to find data on the disc more quickly than its competitor's standards. DVD-RAM media and drives also contain extensive defect-management and error-correction technologies to ensure correct data storage.
- DVD+RW is a similar standard to DVD-RW, but is not supported by the DVD Forum. DVD+RW was developed by the DVD Alliance.
- Like DVD-RW writers, DVD+RW writers will also require dedicated writing software on the computer to write to disc.
- DVD+RW discs do not have a caddy, so they can physically fit in most drives and players.
- DVD+RW discs can be read in DVD-ROM drives.
- DVD+RW supports CD-RW formats and will write CDs as well as DVDs.
- DVD+RW discs can be formatted for sequential data streams (video) or random access similar to capabilities of DVD-RAM technology (data).
- Proponents of the DVD+RW standard also say the standard's built-in defect management makes it equally good for data and video and puts it a step ahead of the Forum's DVD-RW standard.
- Defect management is designed for reliability of data being written to the disc. It uses buffer underrun prevention technology to deal with the interruptions while DVD or CDs lasers are in the process of writing to disc. This technology allows consumers to burn CDs at maximum drive speed without failures. When a PC is interrupting this process, the defect management technology stops the writing, and moves to the next segment of the DVD or CDs next segment. This takes up a small amount of disc space to record the change. When the disc is being replayed, the laser will recognise the interruption and move to the next segment without lack of performance from the user perspective. Because the DVD+RW standard does not support -R discs, the DVD+RW Alliance crafted its own write-once media called DVD+R.
- DVD+R discs store the same amount of information as DVD-R discs (4.7GB) and cost about the same price.
- DVD+R discs are single-sided discs which can only be written to once.
- DVD+R discs can only be written to using a DVD+RW compatible writer. Despite this, the alliance claims +R discs can play in most commercial DVD players and DVD-ROM drives.