DVD Mathematics
David Shamah, The Jerusalem Post January 24, 2006
You know what they say about computers – the minute the newest models comes off the assembly line, it's already obsolete, because back in the lab they've already developed a prototype two generations ahead of the most advanced commercially available systems. As the old saying goes, "If cars had progressed as fast as computers, we would be driving at 500 MPH in a $25 car that gets 2 million miles per gallon and seats the population of China."
This is relevant to many of us who are interested in burning DVDs because most of the computers we are using have CD writers that, at best, can play DVDs. DVD writers are still not de riegeur in discount systems (although over the past half year or so they have become part of many system 'packages'). But if you want to make a DVD, you need a DVD writer – and software to write with, of course.
As is usual with computer technology “DVD” (Digital Video Disc) means different things to different people. DVDs that you stick into a DVD player are known as DVD-Video discs, while DVD-ROMs are used for file storage and creating DVD-Videos on your computer. Within the DVD-ROM world there are several distinctions, including DVD-R, DVD+R (note the plus/minus signs), DVD-RW, DVD+RW (ditto) and DVD-RAM. The R vs RW part is easy to understand; R's let you record whatever you want on a DVD, while RW's let you write, erase and rewrite (up to 1,000 times, according to most manufacturers).
Dealing with that plus and minus business, on the other hand, is a hassle. The +R and -R standards were created and supported by competing companies and standards groups (thre minuses by Pioneer, and the plusses by HP and Sony). Nowadays, newer DVD writers can handle either format, as can most newer DVD players – although some older players are said to have trouble playing DVD+R's, making DVD-R the “most compatible” format. Practically speaking, the type of DVD you end up with depends on what you put into your computer's writer, as both +R's and -R's are readily available in office supply stores (although, as the “senior” format, DVD-R's are generally cheaper).
There's also another player on the field, called DVD-RAM, which is mostly meant for data storage, since the cartridges it uses cannot fir into a commercial DVD player. The media is also more expensive than either DVD-R/+R, but you can't beat them for file storage and backup – RAM's can generally take up to 100,000 rewritings, compared to the paltry 1000 or so times DVD -RW/+RW is capable of..
Despite the confusion DVDs are the only medium really fit to use for recording video, because the file sizes – depending on encoding, of course – can be several gigabytes per hour. With CDs, you're lucky to get 700 MB, while DVDs provide 4.9 GB (9.4 GB for double layered discs, where the top layer on the disc is semi-transparent so that the laser can focus through it and read the second layer). Both sides of a DVD can be written to, if your hardware and software support this, so a double sided/double layer DVD can theoretically hold 17 GB. It's a “theoretical” number, though, because of crazy computer computations (a DVD a kilobyte is 1,000 bytes rather than 1,024 bytes, so you lose a few hundred MB on a 4.9 GB DVD, whose effective file capacity is 4.25 or so GB. To add to the confusion, by the way, DVD capacity sizes are sometimes referred to by their code names: Single-sided DVDs (4.9 theoretical GB capacity) are referred to as DVD 5 discs, single sided, dual layer, 8.5 GB discs are called DVD-9's, double sided, single layer, 9.4 GB discs are DVD-10's, and double sided, double layer, 17 GB discs are DVD-18 DVDs.
CDs can be used for videos, if you're willing to compress way down – most CD/DVD writing software can create a VCD (Video CD) or SVCD (Super VCD) on a 650MB - 700 MB CD, but unless the program is short, it's going to be difficult to write a fully authored video presentation on a either VCD flavor (although, as mentioned, it is possible).
I should also mention that this entire discussion of DVD capacities, and upcoming information on DVD writers and software, is (probably) only going to be relevant for the next couple of years or so. That's because DVDs, which started out as a replacement technology for VHS (which many people considered a perfectly good technology), is about to undergo a replacement itself. Two new DVD formats, DVD-HD and Blu-Ray DVD, are competing to become the next generation DVD standard. The advantages of both these formats is higher storage capacity (between 15 GB and 50 GB, depending on its layering), greater support for codec compression, and support for high-definition video.
Both formats, actually, use a “blue ray” laser beam, which has a shorter wavelength allowing it to read the smaller digital data "spots" packed a lot more densely onto a standard-size disc, instead of the red laser beam currently used in DVD players. Blu-ray is supported by a consortium of major manufacturers, led by Sony, Panasonic, Samsung, Dell, HP, Philips, while HD-DVD is supported by NEC and Toshiba, among others. In what is shaping up as a Beta vs. VHS battle (one Sony intends to win this time), Sony recently announced that its new PlayStation 3 (to be introduced later this year) will use Blu-ray discs, something that will give a definite boost to the format – as will the company's rumored decision to begin releasing its extensive video library on Blu-ray as well. Whatever happens, apparently the powers that be have decided that its time for us to spend more money on new hardware and “software” to play out movies and discs on. Will it ever end? No; this is how these guys stay in business. However, until such time as the formats “officially” change, we need to be entertained, so we will continue this discussion of DVD writing equipment next time.