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Should You Turn Your Computer Off Or Leave It On?

This is a basic concern of all computer owners: how to make the computer last longer. Unfortunately, the answer is more complicated than the question. Some say that if you leave the computer running all the time, it will fail sooner. Others say constantly turning it on and off will break it. The problem is they're both right.

There are two measures of reliability: Mean Time Between Failures (MTBF) and Mean Cycles* Between Failures (MCBF). If you turn something on and leave it on, you've only cycled it once, so you will reach the MTBF first; if you keep turning something on and off, you've hardly used it, but you'll reach the MCBF first.

In general, mechanical components will fail sooner the more you turn them on and off (cycle them). As an example, automobiles which have 100,000 miles on them can be in pretty good shape if all the mileage is highway driving, but automobiles with only 50,000 miles can be wrecks if all the mileage is from stop-and-go city driving. Electronic components, however, will generally fail after they have been powered on for a certain (lengthy) amount of time, regardless of how often you turn them on and off. The problem with computers is that they are made up of both electronic (CPU, RAM, etc.) and mechanical components (hard disk drive, fan, power switch). If you leave the computer running all the time, you will reach the MTBF of the electronic components; if you turn the computer on when you need it, and turn it off every time you're done, you could reach the MCBF of the mechanical components.

My suggestion is that you turn the computer on the first time you need it, and turn it off after the last time you use it. Turning it on (or leaving it on) when you don't need it, will shorten its life, but turning it on and off too many times will also shorten its life.

*A cycle is a change in the operating state of a device. The simplest example is turning something from off to on, but also can include a variety of operating states, such as: standby, sleep, etc.

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Connectors

Quite frequently, a computer will fail, and simply disconnecting everything and connecting it all back up will mysteriously solve the problem. Well, it's really not very mysterious. A connection failed!

Years ago, it was common practice for field repair technicians to simply swap boards which were known to be good, with the boards in the computer that wasn't working. After swapping each board, the technician would test the computer to see if the problem was fixed. If it didn't work, the technician would swap the next board; if it did, the last board swapped was presumed to be at fault as was discarded.

IBM wanted to know what, exactly, was failing on these boards, so it asked its technicians to send the failed boards to a single depot, where the individual components would be tested. What they found was that over 90% of the these boards still worked perfectly! If the technician had simply removed and reinstalled that same board, the computer would have worked.

The reason connectors fail is generally environmental. Often, the connector's copper or gold contacts will oxidize, breaking the electrical connection. Sometimes, during a computer's operation, the components in the case will expand with the increased heat, which can then cause a connection to fail. And sometimes, vibrations from the computer fan, or from other equipment nearby, can cause a connection to shake loose.

This is one of the reasons that laptop computers are slightly more reliable than desktops. Laptop computers include a lot more features which are integrated into the computer logic board, so laptop computers have significantly fewer connections than desktop computers.

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Network Computers

Network computers (NetPCs, thin clients, etc.) are nothing new. In fact, they have actually been around for quite some time. They just went by a different name: Terminal.

In the early days, computers didn't have consoles (keyboards and screens), they just had hexadecimal keypads and nixie tubes (vacuum tubes which contained a variety of filiments, each shaped like a different number) on the front panel. Connecting a single keyboard and monitor to the computer was a huge advance in the computer's user interface. After one terminal was connected, it was a simple matter to connect additional terminals. These were what we call today "dumb terminals", but during the advent of the PC in the workplace, in a last gasp attempt to preserve the superior position of the mainframe computer, terminals got smarter and smarter, doing more and more local processing (checking for data entry errors, mostly). In today's "Windows PC" world, Citrix and Wyse have systems composed of a central Windows Server and Windows terminals. The drawbacks to these are the same as the drawbacks to the earlier terminals:

  1. They depended entirely (or to a great extent, depending on the system) on the processing speed of the central computer. If someone else is running a processor intensive application, you will be locked out until they are finished. And the more terminals that are connected, the more frequently that will happen.
  2. Portable terminals are inconvenient and slow. What's a NetPC without the network? And if you bring the network with you, via a modem, then all the processing must be transmitted through the modem at 56 KiloBITS, or 5.6 KiloBYTES per second. The alternative is that Information Services Departments would have to support laptop PCs under any circumstances. So if they must support PCs for their mobile users, why would they want to support different systems for their stationary users?

For years, market research organizations like DataQuest have been predicting booms in the laptop market and in telecommuting. It seems to me that either of these two trends should quelch any possible resurgence in terminal usage, but the rumors persist despite all rational considerations.

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Power Protection

There are quite a number of things that can go wrong with your electrical service that can adversly affect your computer. The first and most obvious is a power failure, where all electrical power is lost.

Power failures fall into two categories. The distinction is whether they last less than 6 seconds, or greater. Power failures of less than six seconds are when a circuit breaker has tripped in a substation somewhere, and the circuit breaker was able to reset itself. Power failures of greater than six seconds are when the circuit breaker cannot reset itself, and an operator must intervene. This can involve downed power lines, fires, etc., and can take quite some time to resolve. Obviously, a computer cannot operate with no electricity, but a power failure, in and of itself, will not harm your computer. Computers can, however, be damaged by the condition of the power immediately before and immediately after the power failure. There is also the potential for lost data and currupt files.

Another power hazard is variations in the voltage level: overvoltages or undervoltages. These typically occur when other devices on the same circuit (not necessarily inside your house or appartment) draw either significantly more current than normal or significantly less. For example, construction in your neighborhood or a stuck elevator in your building can cause either of these conditions. Undervoltages can also be caused by your utility company, and are called "brown-outs". These can cause components in the computer to run too hot, or affect the timing between devices.

A large, quick overvoltage is another power problem, and is called a surge. Surges are caused by lightning strikes and failures in electrical distribution equipment, and frequently occur before and after power failures. Surges can overload components and cause them to fail.

Line noise is when a high frequency signal is riding on the frequency of the alternating current. With Direct Current, or DC, the electrons are constantly traveling in the same direction through the circuit. With Alternating Current, or AC, the electrons are constantly changing direction, 60 times a second or 60 Hertz (Hz), within the circuit. Other devices on the circuit, such as radios, electic motors, and even other computers and monitors, can generate higher frequency variations withing the 60Hz AC. If the frequency of the line noise coincides with the frequency of any of the components of the computer, it might affect the operation of those components.

Protecting Yourself

Surges and Line Noise

Surge suppressors are designed to divert surges away from your computer equipment and filter out line noise. In general, they do a good job, but quality varies greatly. Some surge protectors will divert the first few surges, but let subsequent surges through without notifying you of the condition. The best indicator of quality is reputation. T C Solutions recommends Tripp Lite products, though there are a number of quality products on the market. A $6.99 surge suppressor at your local home improvement superstore probably isn't a good way to protect your $2000 computer system. Expect to spend $40-$70.

Overvoltages and Undervoltages

Voltage regulators can protect your equipment from these hazards, but so can some UPSs. Consider a Line-Interactive UPS.

Power Failures

To protect against power failures, you can employ an Uninterruptable Power Supply (UPS) which, in its simplest form is a battery backup. UPSs come in three flavors: Backup, Line-Interactive, and On-Line. All three include surge suppression and Line Noise Filtering.

The Backup (or Standby) UPS

The Backup UPS provides backup power when the utility power fails. Utility power usually is from 115 to 120 volts. When it drops below about 90 volts, the Backup UPS switches its outlets to run from its internal batteries. When the utility power returns to above 90 volts, the Backup UPS switches its outlets back to the utility power, and at the same time, recharges its internal batteries so they will be available for the next power failure. The switching time is typically less than 1/100 second, which is fast enough for most computer equipment.

The Line-Interactive UPS

The Line-Interactive UPS adds a voltage regulator to the Backup UPS. In addition to providing battery backup, the Line-Interactive UPS will correct unvervoltages and overvoltages. For most applications, this is the best protection available.

The On-Line UPS

The on-line UPS bypasses any problem that might arrise due to the switching time associated with the Backup UPS by constantly supplying power to its outlets from its internal batteries, and only using the utility power to recharge these batteries. This eliminates the switching time of the Backup UPS, and is generally only required by high-speed telecommunications equipment and the healthcare industry.

What's a VA?

Good question. A VA is a VoltAmpere. Does that help?

Didn't think so. UPSs are available in various sizes. You need to know how much stuff you're going to plug into a UPS to determine how big a UPS you need. Add up the current (in Watts) of all the items you will plug into a UPS, and multiply the result by 1.4. If you have a computer with a 200 Watt power supply, and your monitor draws 100 Watts in normal operation, that's a total of 300 Watts. Multiply 300 by 1.4, and the result, 420, is the smallest UPS, in VA, that you should use.

Remember: It doesn't make much sense to have your computer plugged into a UPS, and not the monitor! How can you select the command to shut down the computer if you can't see your mouse pointer?

A computer with a 200 Watt power supply will probably not draw 200 Watts during normal operation. It will probably only draw about 90 to 120 Watts after it starts up (unless you're playing a 3D game. These games can cause a computer to draw quite a lot of power.) If the devices plugged into the UPS ever draw more than the UPS is rated for, then the UPS can be damaged.

A UPS under full load (for example: a 420VA UPS with devices connected drawing 300 Watts) will provide between 5 and 10 minutes of protection. That's plenty of time to save everything and shut down. You should not consider continuing to work (or play) because if the power failure lasts longer than 6 seconds, then it will probably outlast the capacity of the UPS.

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