When comparing Blu ray vs DVD optical disc formats there are several factors to examine.
The most fundamental difference between DVD vs Blu ray is the disc structure. For DVDs, two discs are manufactured separately and then glued together top side to top side. This results in the data and metal reflective layers residing in the center of the disc structure. For Blu ray, there is only one disc and the data and metal layers are very close to the base or reading side of the disc. Because these layers are so close to the base of the disc, an extra protective layer exists on the base side, something not present with a DVD.
The pits or spot which represent the digital information on the optical disc are smaller for a Blu ray vs DVD and there is a tighter winding of the spiral track groove holding the data on a Blu ray. This allows the storage of more information on a Blu ray than on the same sized DVD optical disc.
To read the different sized data spots and tighter spiral configuration, different lasers are a necessity when reading a Blu ray vs DVD. A DVD uses a laser of 650nm, whereas a Blu ray laser is 405nm.
The main difference between the DVD and Blu ray movie discs is the resolution. For DVD, the resolution is 720x480i, which means 720 pixels displayed across the screen horizontally and 480 vertically. The ‘’i” stands for interlaced, which means for a DVD, 480 lines are displayed vertically on the screen in an alternating pattern. To increase image quality by producing a smoother image, progressive scan DVD players were introduced that increased the resolution to 720x480p, “p” representing progressive. The vertical lines no longer alternate but instead follow sequentially.
For Blu ray, the resolution is 1920x1080p or 1920 pixels across the screen horizontally and 1080 pixels or lines vertically and displayed progressively. This results in six times more pixels and much better image quality.
Although DVD and Blu ray movie discs can come in different structures, in terms of number of data carrying layers, the most common are the dual layer movie discs. These are discs with two data layers both readable from the same side.
The movie formats are read-only and they are not the only types of optical discs available when comparing Blu ray vs DVD. There are also recordable once and erasable/rewriteable formats. For DVD, the recordable formats are DVD-R and DVD+R, which are single layer discs. There is also a DVD+R DL, which contains two data layers instead of one. The erasable DVD format is either the DVD-RW or DVD+RW, both only in single data layer configurations.
For Blu ray, the recordable format is BD-R single layer and dual layer, but also the much less popular BD-R XL with three or four data layers. The rewriteable or erasable formats are like the recordable ones, namely BD-RE (single layer), BD-RE DL (dual data layer), BD-RE XL (three or four storage layers).
Finally, what is the capacity of Blu ray vs DVD? The capacity of each disc varies according to the number of layers in each disc format. For the DVD movie format, the following capacities are possible:
For the DVD-R, DVD+R, DVD-RW, and DVD+RW formats the capacity is 4.7 GB, whereas the DVD+R DL has a capacity of 8.5 GB.
For the Blu-ray formats the capacities are: