I'm typing this on a 3-year old PC laptop which is still going strong thanks partly to a new hard drive (the old one went to a new home via eBay) and additional memory. The most processor-intensive application I use is probably Photoshop CS, which despite not exhibiting Ferrari-like performance, operates more than adequately. Besides, it's good to test your patience.
Despite looking longingly at the G4 Powerbook, I see no practical reason for replacing this workhorse for some time to come (touch wood, or, rather, composite plastic).
Lucky me. As Moore's Law continues to hold true, a significant number of computer users wholly replace their machine, on average, every two years. Modern software such as PC games, digital photo applications and even the most popular operating systems (MacOS X, Win XP) demand powerful home computers with multi-GHz processors and 512MB RAM or more. This need for speed, combined with ever-decreasing prices and ever-increasing advertising budgets for manufacturers, makes people ditch their 'old' machine and upgrade.
So what happens to these old PCs? Surely people don't take them to the tip when there are schools/hospitals/charities/small businesses which could undoubtably benefit from them? Well, sadly, in our disposable society this is not the case. We bin them.
Not only does the 'e-waste mountain' contribute to our bloated landfill sites, but the pollution resulting from it, combined with the effects of the energy-intensive manufacturing process of computers, is huge. Scientists at the UN university in Tokyo have estimated that making a new computer requires 240kg of fossil fuels, 22kg of chemicals and 1,500kg of water. The Silicon Valley Toxics Coalition have calculated that microchip production involves more energy, water, fossil fuels, toxic chemicals, and elemental gases than any industry in history.
"One semiconductor plant can require enough electricity to power a city of 60,000 and several million gallons of water a day."
Given that there are over 700 million personal computers in use throughout the world, and with annual computer sales running at over 170 million, that's a pretty serious environmental impact.
So how can this waste be reduced whilst allowing progress to continue uninhibited? Recycling rather than disposing is obviously the place to start, but whilst necessary to recover valuable metals, even this can be environmentally damaging (using acid baths to strip circuitry, for example).
The best possible way forward is to make PCs last longer, which means making them easily extensible as well as expandable. Expandability has been around, to some degree, since the dawn of the PC (adding a second hard drive, adding more RAM, replacing graphics cards) but it remains prohibitively difficult to do. The average PC user has trouble understanding Office Assistant, never mind replacing a motherboard.
Surely, in the age of nano-technology, a PC can be developed which provides easy upgrade of all it's components? I understand that we currently have chipset and bus speed incompatibilities, but perhaps these are introduced by the manufacturers for convenience or as a method of ensuring they sell more units? A combined effort between manufactures and designers could easily overcome problems like this and result in benefits for the environment and consumers alike, whilst not necessarily adversely affecting profits.
In today's world, profit-seeking is inevitable but, like the PC waste mountain, year-on-year growth simply isn't sustainable. It may take consumer demand, government regulation or an all-out miracle for these changes to happen, but until they do we're facing problems as abundant as cheap PCs.
-  National Safety Council, "Electronic Product Recovery and Recycling Baseline Report: Recycling of Selected Electronic Products in the United States", May 1999
-  Silicon Valley Toxics Coalition, "Fourth Annual Computer Report Card, January 9, 2003". https://www.svtc.org/cleancc/pubs/2002report.htm
-  Source: Computer Industry Almanac. https://www.c-i-a.com/pr0203.htm
-  Source: https://www.pcworld.com/news/article/0,aid,119347,00.asp