When you are ready to buy a new computer, your first decision is whether to purchase a desktop or a laptop computer.

Now that might sound like a fairly easy decision, but there are many things that you need to know before you can make an intelligent choice.

The main reason people purchase laptop computers is portability. It's great to be able to grab that small computer and hit the road. It's perfect if you are traveling, but even when you are at home, you can use it in your local area.

Free wi-fi hot spots are available almost everywhere. So you can use your laptop while you have a cup of coffee at Panera, a hamburger at McDonalds, or an ice cream cone at Cold Stone Creamery.

If you purchase a wireless router, you can also enjoy using your laptop in any room of the house, on the patio or in the garage.

There are, however, things that you give up for that portability. First, although prices are competitive, you will find that laptops are a little more expensive than desktops. Next, you give up expandability.

Desktop computers usually have open bays which you can use to install additional equipment such as television tuners, DVD players and extra video cards. This is not as critical as it once was. There was a time when almost all components needed to be installed inside the computer. That is no longer the case.

Now you can add many components via USB. If you want to add a television tuner or an extra hard drive, you can add one to a desktop or a laptop via the USB port.

What you cannot do with a laptop is upgrade it easily. You can sometimes add more memory to a laptop, but that is about all you can do. If you decide you would like to have better sound or video, you can easily install a new audio or video card into a desktop, but upgrading the components of a laptop is much more difficult and more expensive.

This is also true of repairing a laptop. If the power supply or a fan on a desktop goes out, it is a fairly easy and inexpensive repair. On a laptop, it requires a more expensive proprietary part and more knowledge of how the laptop is built. So most of the time you wind up sending it back to the manufacturer for an expensive repair.

For laptops to be lightweight and compact, the components are often more tied to the motherboard than they are in a desktop. So again, what may be an inexpensive repair for a desktop becomes an expensive repair for a laptop. The tightness of the components also generates more heat, which decreases the longevity of the components.

Because the components usually don't last as long, because laptops get carried around and beat up more and because repairs are more expensive, you can expect a laptop to have a shorter life span than a desktop. I have not read any formal studies on this, but the computers that I see for repair bear this out. It is not unusual for a laptop to last only two or three years. I personally had a laptop that only lasted two years.

That said, however, I also have my original Windows XP laptop that has traveled around the world with me and has never needed a repair. Although the battery won't hold a charge anymore, the laptop is still going strong after eight years of heavy use and travel. So while you can expect that you will probably have to replace a laptop sooner than a desktop, there is no hard and fast rule about it.

One of the biggest differences between a desktop and a laptop is that a laptop has batteries that let you use it without being tethered to an electrical outlet. It's a wonderful concept that works well until the battery starts to wear out.

Depending on usage patterns, the battery can become a doorstop in as little as two to three years. Replacement batteries can cost as much as $150. So if you are thinking of purchasing a laptop, be sure to build that cost into your budget.

Many people want to use a laptop like a desktop computer when they are at home. This is very doable. You can easily hook up a large monitor, keyboard and mouse. Then you simply adjust the settings on the portable so it will not turn off when you close the lid. Put the laptop on the side of, or under the desk, and it is just like having a desktop computer.

The bottom line is that if you don't need the portability that a laptop gives you, buying a desktop computer is more economical in the long run. If, however, you need or want portability, go for the laptop. It may cost more in the long run, but it's worth it if adds to your computer enjoyment.

Sandy Berger welcomes all of questions and comments on today's column. Please post them on the Compu-Kiss Message Board at www.compukiss.com/happycomputing.