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"  Double-Decker Disks I&amp;#039;m interested in a new DVD burner and I&amp;#039;ve noticed that many new burners are dual-layer drives. How do these things work and will the discs play in nondual- layer drives and DVD players? A standard single-layer recordable DVD can carry 4.7GB of data, which may seem like a lot, until you notice that a standard store-bought movie DVD has up to 8.5GB of data on it. That&amp;#039;s because Hollywood has been pressing movies onto high-capacity dual-layer discs for years. The bottom recording layer of dual-layer discs is semitransparent, and burners and players make a minute adjustment in the focus of the laser&amp;#039;s lens to read the upper layer of the DVD through the bottom layer. There is a difference between Hollywood&amp;#039;s factory-pressed DVDs and burnable dual-layer DVDs. Pressed DVDs use a reflective layer stamped with physical bumps that represent the digital 1s and 0s that make up a movie, whereas burnable DVDs use an organic dye that changes its opacity when exposed to heat -- mimicking the bumps of pressed DVDs. Now, you may be wondering, if a single-layer DVD has 4.7GB of capacity, why doesn&amp;#039;t a dual-layer disc have 9.4GB? A representative from the DVD Forum explained to us that extending a DVD player&amp;#039;s laser beam to the upper layer of the disc requires larger pits and bumps (or lands) to ensure clear readability -- reducing capacity by about 10 percent. I&amp;#039;ve found that dual-layer discs I&amp;#039;ve burned usually work in my standard DVD player, but there&amp;#039;s no guarantee. The situation is similar to when CD burning came of age a few years ago -- older hardware will be less likely to read homemade discs, while newer hardware probably will read it just fine. At this point, dual-layer DVD burners are nearly the same price as single-layer burners, so you should definitely get one if you&amp;#039;re in the market. Sadly, dual-layer blank DVDs are more expensive than single-layer ones. As with everything shiny and new, manufacturing capacity and demand must increase for prices to fall. Map Quest  KNOW YOUR STUFF ExpressCard  You&amp;#039;ll notice a change to the side of your next laptop. The PC Card expansion slots that you know and love are disappearing in favor of a new standard: ExpressCard. According to Richard Shim, an analyst at the technology market research firm IDC, ExpressCard is predicted to be in about 18 percent of new laptops by the end of the year. ExpressCard transfers information at up to 2.5 gigabits per second (more than twice as fast as a PC Card), making it ideal for graphics and video. It comes in 54mm and 34mm widths; both sizes fit in the same slot. One thing that won&amp;#039;t fit in ExpressCard slots, however, is your old PC Card. --Glenn Derene  I recently bought a small, stick-to-the-window navigation system, and I use it all the time. But I travel a lot and I am wondering if it will work in foreign countries. If so, where can I get the map data? From a hardware standpoint, the basic GPS unit should work anywhere in the world. (It is &amp;quot;global&amp;quot; after all.) There is a chance that you cannot add new map data, but most modern GPS units let you load new maps in one of two ways. Higher-end models -- including, I suspect, the stick-to-the-window unit you bought -- have an SD flash memory card slot from which they pull map information. Loading another map set would be as easy as purchasing a new set of maps (costing anywhere from $75 to $400, depending on make and model) and popping in the card. Other models use either built-in flash memory or an internal hard drive. In that case, you&amp;#039;ll have to order a CD from the manufacturer (the price is about the same as that of an SD card) and copy the map data over to your unit from your PC. European map data is available from almost every GPS manufacturer, while map data for Asia, Africa and other regions (with place names in English) are not as common. Garmin&amp;#039;s Web site has a list of third-party MapSource developers that sell maps covering areas that Garmin does not. It is possible to add custom-created data compiled by GPS aficionados (as long as you trust their skills). If you own a Garmin GPS unit (or one that uses the company&amp;#039;s MapSource standard), you can access a variety of free maps at mapcenter.cgpsmapper.com. You can even use the freeware tools at cgpsmapper.com to create your own maps from publicly available topographic maps. If you get really plugged into GPS map creation, Rich Owings, author of GPS Mapping: Make Your Own Maps, runs a nice blog on the subject at gpstracklog.typepad.com. Clean Slate I don&amp;#039;t like to leave temporary Internet files, cookies and browsing history on my computer after my Web surfing sessions. Is there any automated way to clean up after myself when I shut down my browser? In Internet Explorer, automatically clearing your temporary Internet files is simple. Select Tools from the menu bar, then click on Internet Options. Inside the box that opens, select the Advanced tab, then scroll to the section labeled Security. Check the box that says &amp;quot;Empty Temporary Internet Files folder when browser is closed,&amp;quot; then click on the Apply button. Easy as pie. Firefox makes it pretty easy, too. Simply select the Tools menu, then Options. Click Download History, then the Settings button in the lower righthand corner to bring up the Clear Private Data menu. There, you can choose to clear almost everything automatically, including browsing history, cookies and temporary Internet files (called Cache in the Firefox parlance). But let me point out something: Cached files speed up your browsing experience by obviating the need to redownload content from frequently visited Web sites. Sure, if you have several gigabytes of temporary files, it could start to clog up a slower machine&amp;#039;s browser, but clearing them out every time is probably overkill. If your concern is less about browsing speed and more about privacy issues, then you might want to go whole-hog and consider something like FoxTor (cups.cs.cmu.edu/foxtor), a package that combines Firefox, Tor (The Onion Router), and Privoxy to completely mask your browsing habits. "^^<http://www.w3.org/2001/XMLSchema#string>
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