DVD-R and DVD-RAM are different formats of writable DVDs, discs you can use to store video, photos or data. While they're similar in their basic purpose, the two formats differ greatly in most aspects. Understanding these differences can help you determine which format is better suited for your needs.
Reuse and Longevity
One of the biggest differences between the DVD-R and DVD-RAM formats is that data stored on a DVD-RAM disc can be removed or written over, while a DVD-R disc can be burned only once. The similar format, DVD-RW, also features rerecording capabilities, but even DVD-RWs aren't as useful. DVD-RW discs can be rewritten only about 1,000 times, while DVD-RAM discs can see 100,000 rewrites. When it comes to overall longevity though, manufacturers estimate DVD-R discs have lifespans ranging from 30 to 100 years, while the DVD-RAM disc's lifespan is estimated to be a maximum of 30 years.
DVD-R and DVD-RAM discs use different recording methods, which explains why DVD-RAM is reusable and DVD-R isn't. DVD-R discs feature a layer of recording dye that the disc drive's laser burns and alters into a pattern designed to mimic the pits on a commercial DVD. The dye can be burned and molded only once. DVD-RAM uses phase-changing technology with a surface capable of being reformed after the initial use. DVD-RAM discs also feature random access characteristics and hard sectors similar to those in RAM and hard disks, separating them from phase-changing-only technologies such as DVD-RW.
One of the largest differences between the two formats is compatibility. For creating each type, you'll need a burner specifically designed to read the type of media you're using. For end use, DVD-R is much more compatible and capable of being played in most DVD-ROM drives and home DVD players. DVD-RAM discs often come in cartridges, which makes it impossible even to put them in a normal disc drive. To read the DVD-RAM format, you'll need a device specifically designed to do so. Format changes throughout the product's lifespan have further complicated the picture in that not all DVD-RAM readers can read all DVD-RAM discs. For example, many recorders designed specifically for 2.5 or 5.2 GB DVD-RAM discs can't read 4.7 or 9.4 GB DVD-RAM discs.
Physical Size and Capacity
The DVD-R and DVD-RAM formats differ physically, as well. DVD-R discs are always 80 or 120 mm discs similar to mini-discs and full-sized DVDs. DVD-RAM discs often come in cartridges designed to fit into DVD-RAM readers. The discs inside the cartridge are also either 80 or 120 mm. While both disc formats have a maximum capacity of 4.7 GB for a single-sided disc, DVD-RAM allocates the space better so you get the full 4.7 GB, whereas only about 3.95 GB of space on a DVD-R is actually usable.