20 Things They Don't Want You to Know

We reveal some of what vendors are keeping mum, such as: You never have to pay full price, extended warranties rarely pay for themselves, and the big sites do have customer service numbers.

Useless Specs

Digital Zoom

Not all zoom is created equal. While optical zoom uses the camera's lens to increase magnification, digital zoom uses software built into a camera to magnify a subset of an image captured by a lens. The software does this by upsampling (or interpolating) pixels--generating new image data based on samples from the original pixels. That process can degrade the quality of the photo, making it blurry and pixelated. Optical zoom is the important number to look for.

Response Time and Contrast for LCDs

An LCD's response time is supposed to tell you how well a monitor will respond to fast-moving images. Unfortunately, LCD manufacturers measure response times in so many different ways that the figures they quote are pretty much useless, as we found out in "LCD Specs: Not So Swift." And contrast ratios aren't much use either. In June 2003, we found monitors that underperformed their ratings by more than 50 percent.

Speaker Wattage

Speaker manufacturers have a bag full of tricks they can use to inflate the power ratings of their speakers. But wattage should be pretty low on your list of deciding factors, especially for PC speakers. As any audiophile will tell you, there's no substitute for a good listening test when you're shopping for speakers. So put down the spec sheet, pick up a CD you're familiar with, and listen before you buy. If you insist on comparing speaker specs, look for a figure labeled Watts RMS that's broken down by channel instead of combined into a number representing total system power.

Burst Transfer Rate

Hard-drive marketers like to push big numbers, such as a drive's burst transfer rate. But that number has little meaning. A typical Serial ATA drive can transfer bursts of data at 150 MBps when exclusively writing to or reading from its cache. But that doesn't happen often. A drive's sustained transfer rate or internal transfer rate (usually around 65 MBps), has more bearing on performance.

Eric Dahl is a senior editor and Grace Aquino is a senior associate editor at PC World.