Next, decide if you want to do a basic wipe, a government wipe or more. A basic wipe will write a 0 on every drive sector in one pass. A basic wipe is fastest and cheapest, but it leaves traces. Motivated hackers could possibly retrieve the data under the 0s.

The US Department of Defence standard 5220.22-M (a standard exceeding Australia's NPP 4.2) dictates a stronger scrub. The so-called government wipe makes three overwrites on the disk. The first wipe puts 0s on sectors, the second, 1s, and the third, a random character. The more times the process is repeated, the less likely anyone could get anything off the drive.

More scrubbing means more time (and money). A single overwrite on a 40GB hard drive can take 20 minutes. A government wipe can take up to three hours.

A more secure option exists: degaussing, in which a giant magnet delivers negative and positive jolts to the hard drive, destroying it. But since the hard drive accounts for about two-thirds of the recovery value of an old PC's parts, degaussing carries a steep cost.

Quick Fact: Don't Quit Your Day Job to Mine Computers! The combined worth of the precious metals (gold and silver) in 5000 PCs is only about $300. Newer PCs have even less.

Quick Fact: No Tax Break for You! In Australia, companies can only claim a tax deduction if the equipment being donated is less than 12 months old. (Current local accounting practices usually fully depreciate PCs over a three year period.) It's a puzzling disincentive to doing the right thing with old equipment.

Step 3: Finally, Send Them to Their Reward.

The disposal guys call it "shred, grind, separate, refine, smelt, melt and pelletize"

After their disks have been wiped, computers head off in various directions. Some get a light dusting and a technical refresh and are shot off to the secondary market for resale. Others are pegged for donation. Companies with a truly thorough asset management plan might even redeploy some, turning old desktops into, say, Linux servers. Older, less useful computers can be cannibalized for parts.

After all that, what's left are the dregs.

The dregs include three types of materials: recyclable commodities, recyclable precious metals and poison (see "The Weight of Waste", below). Proper disposition gets labour- and cost-intensive here. Computers take time and a lot of labour to disassemble. According to one published report, a disposition company once told the US Government Accountability Office (GAO) that to remove the lithium battery from a single Hewlett-Packard computer required the removal of 30 screws.

Once a computer has been disassembled, the parts that have no reuse value head off to a violent death. They will be run through any number of large, expensive machines in a process the International Association of Electronics Recyclers describes as "shred, grind, separate, refine, smelt, melt and pelletize". Different materials are ground into different sizes, from the size of a quarter to the size of a pinhead.

Metals and plastics are sold to dealers by the kilo. Toxic waste is shipped off to an environmental disposal company. Precious metals are dealt with as well. Some disposition companies perform these processes themselves. Others offload the heavily regulated toxic waste disposal and partner with companies that specialize in those specific environmental processes. CIOs should make sure that the disposition and environmental disposal companies they deal with carry "errors and omission" insurance as well as pollution insurance. The prices these commodities bring, minus the cost of disposal, help to offset the overall disposition costs.

Quick Fact: The Smell of Dead Digits A shredded hard drive produces about two cups of digital "mulch", which has an oddly sweetish smell, something like petroleum mixed with sugar.

MONITOR MALAISE

Loaded with as much as 1.8 kilograms of lead, CRTs require extra money and care for proper disposal. What's more, the leaded glass inside a CRT ("cullet") is hard to recycle, and its reuse is limited by regulators. In 2000, 13.6 million kilograms of lead-bearing CRTs were trashed, and by 2030, that total will rise to 180 million kilograms.

The Weight of Waste

What 5000 computers contain

Other 330kg

Nickel 1.75 tons

Tin 1.75 tons

Zinc 3.5 tons

Lead 10.5 tons

Copper 12.25 tons

Aluminium 24.5 tons