The U.S. Environmental Protection Agency (EPA) confirms that putting desktop PCs in a low-power sleep mode after a period of inactivity can lead to annual energy savings of $15 to $45 per computer. The EPA breaks sleep mode down into two categories: "system standby" and "hibernate." System standby wakes up faster than hibernate (five to 10 seconds compared with 20 or more seconds) but does not save work in the event power is interrupted or lost. This is because in system standby the PC saves work to RAM, whereas in hibernate it saves to the hard disk, which records data magnetically, thereby retaining it even when the power is cut.
If the EPA's projected cost savings fail to dazzle, there are other incentives for using computers more efficiently. The EPA says that PCs adhering to its latest Energy Star specifications are expected to save consumers and businesses more than $1.8 billion in energy costs over the next five years and prevent greenhouse gas emissions equal to the annual output of 2.7 million vehicles. Desktop PCs meet Energy Star qualifications if they use two watts or less of electricity in system standby mode, five watts or less in sleep mode and no more than 60 watts in active mode. Laptops qualify under Energy Star if they use 0.5 watt or less in standby, five watts or less in sleep and 15 watts or less in active mode.
When it comes to judging whether sleep or standby causes more wear and tear on your computer, pick your poison. Whereas disk hard drives are most likely to crash during the process of turning off the computer, leaving the PC on causes the microprocessor to generate heat—more heat than if the system is shut down—that will wear down the electronics over time. "Some components will last longer if you shut down your computer, others won't," Bosley says.
As a general rule of thumb, he says, most electronics have some failure rate linked to the amount of hours they're in use. A few hundred dollars will buy you either a blazing-fast new microprocessor or a spacious, terabyte-size hard drive, so the replacement cost differences are negligible.
Of course, the importance of whether to power down or put your computer to sleep depends a lot on how much you use it. If you spend 20 minutes each night reviewing your e-mail, it's a waste of energy to leave your PC on all day. If you're continually on your computer, or go back several times a day, it's best to leave it in sleep mode between sessions. Another variable is the efficiency of the PC's processor. Slower ones use less energy but have to work longer and harder than more powerful CPUs. "It's like a car," Bosley says, "you can't talk about gas mileage without talking about the vehicle's performance."
Ultimately, if you want to leave your PC on most of the time, your best move is to buy one that meets the EPA's Energy Star efficiency standards—Energy Star–approved PCs consume less than half the amount of energy as products without this designation—and also to make sure your computer defaults into sleep mode if it is inactive for any length of time. That sort of compromise will make sure your computer is ready for action on a moment's notice without padding your utility bills.