Personal computers are notorious for having a half-life of about two years.
In scientific terms, this means that two years after you buy the computer, half of your friends will sneer at you for having an outdated machine. In households with children, the half-life is closer to six months. At 24 months the owner will probably begin to worry about upgrading the computer with new memory chips, a new processor, a faster CD-ROM drive, a bigger hard disk, a faster modem, a new operating system, a software upgrade or some gadget that was not invented when the machine was new. True, automobiles also begin losing value the minute they are driven from the showroom. They may need periodic repairs, and they eventually wear out.