On a DVD
Q. When I burn a DVD, I have room for about two hours of recorded video on the disc. However, I recently bought a DVD recording of the opera "Carmen" that is more than three hours long. How can this much video fit on a DVD and why can't I do it, too?
A. Digital videodiscs can store different amounts of information, depending on the number of data layers available. A DVD with a single layer for storing data can hold up to 4.7 gigabytes. A DVD with a double layer for storage (also called a "dual-layer" DVD) can store up to 8.5 gigabytes of data.
So the amount of recorded video you can fit on a disc varies based on the type of DVD you use (and what your recorder can handle), as well as the quality of your recording. Some DVD burners and recording programs also offer different video-quality modes, where the lower the quality, the more video you can squeeze onto a disc.
Your DVD recorder is probably using single-layer discs. Most commercial DVDs, like those for Hollywood movies or opera performance recordings, use the dual-layer discs to hold a greater amount of video at a higher quality -- and still have room for things like bonus features. If you have ever watched a movie on DVD and noticed a slight pause or stutter about halfway into the film, you are most likely hearing the DVD player shift from one data layer to the next on the disc inside.
How to Hunt
For a Perfect Phone
Q. I will soon have to replace my ancient 10-year-old cellphone with a smartphone -- but which one? I have not been able to find up-to-date substantive details comparing the major Apple and Android smartphones. Do you have any advice on where to find such information?
A. The amount of smartphone choices out there can be overwhelming, but there are a few factors to consider when beginning your search. Your wireless carrier won't carry all models, so unless you plan to change companies, you may want to start with the handsets your carrier supports. The company's Web site should list the models it sells and you can find reviews of those phones on sites like CNet (reviews.cnet.com/smartphone-reviews) and PCMag.com.
If you don't have a wireless contract or loyalty to your carrier, be sure to check that the mobile company you choose has adequate coverage in your area. You can find coverage maps on the carrier Web sites.
One way to approach the phone search is to make a list of features you want -- like a good camera, a big screen, a particular hardware brand -- and then see what smartphone meets your wish list. Comparison sites like WhistleOut (www.whistleout.com/CellPhones/Phone-Finder) and PhoneArena.com give you a screen full of options to whittle down.
TIP OF THE WEEK Google Plus can automatically back up pictures taken with Android phones and tablets, but Google's social network has a few other features as well -- like photo-editing right in the Web browser. When in your Google Plus Photos collection, click a picture to open it. On the next screen, click the Edit button to get to a set of tools you can use to crop, rotate and resize the image right in your Web browser.
On the editing screen, you can also adjust the photo's exposure and color balance manually -- or click the Auto-Fix button to have Google Plus automatically enhance the shot for you. You can also add filters, text and other elements to jazz up the picture.
Personal Tech invites questions about computer-based technology to QandA@nytimes.com. This column will answer questions of general interest, but letters cannot be answered individually.
This article originally appeared in The New York Times.