Most computer users are vigilant when it comes to the possibility of virus attacks and other technological threats. There is, however, one potential disaster that can strike anywhere, anytime, that's not taken seriously by some - the possibility of a power outage. A preventative UPS device is much more valuable than an expensive cure.
A UPS (uninterruptible power supply) is a device that allows your computer to keep running for a relatively short time when the primary power source has been lost. The UPS may have one or a number of batteries that keep the power flowing, even through a blackout. They also provide protection against spikes, sags, surges, noise, lightning, and brownouts. A UPS can be more than just a safety net. It can regulate the power that comes from your wall socket. The UPS can ensure all your 240-volt power devices always receive clean and smooth power. Some of the better UPSs ship with software that will let system administrators monitor the status of the UPS from a remote location via a network node or the Web. Some software can also e-mail users, letting them know there is a problem in the server room. If the power does not come back up before the UPS is depleted, the software can initiate a system shutdown. Users are warned of the shutdown and their files are automatically saved prior to the shutdown.
There are two basic types of UPS. The first is called a standby power system (SPS), which monitors the line and kicks over to battery power as soon as it detects an outage. With this type of UPS, there's a millisecond lag during which your machine is powerless. The second type, an online UPS, provides a constant stream of power--but is more expensive. All the UPSs we tested for this month's feature were of the second type. These UPSs constantly monitor the integrity of the power by boosting or reducing the voltage to your PC whenever the line voltage rises too high or falls too low. They will also switch to battery power if the deviation becomes too great. This gives it a great advantage over standby UPSs. Standby UPSs switch between utility and battery power when utility power fails. They maintain stable system operation when utility power is unstable but the only drawback is that they use a smaller charger. The charger takes longer to recharge the batteries, and while this is happening, for over a period of a few hours, the UPS will deliver little or no backup protection.
The capacity of a UPS can be measured in power (measured in volt-amperes or VA) and energy (measured in watt-hours). Power determines how much equipment the UPS can operate and energy determines how long the UPS can operate your equipment. All the UPSs in this roundup use some sort of sealed lead acid battery. The rated lifetime is three to six years and as the batteries age, runtime also gradually declines. Software plays an important role in shutting down your equipment. UPS software works by polling the UPS, then posting all of its operating parameters such as battery capacity, input voltage, output voltage and battery voltage. Some software will let you schedule a system shutdown, graph any power problems and schedule events and create multiple logs. The relay of control information between the UPS and software is by way of a RS-232C serial port or 10Base-T network connection.
For this comparison we decided to only test true line interactive UPSs that are rated between 600VA and 1000VA. UPSs of this rating are suitable for PCs, workstations, and small servers. The RMIT IT Test Lab received 11 UPSs in total--three of which were rack mountable. Most of the UPSs shipped with power cables and support Windows, OS/2, Netware, and many Unix variants.
