Aspects of Energy Consumption and Saving in Computer
We are living in the era of computers. We are using computers in every field and we always measure the performance of computers in terms of speed and portability. But do we ever have spoken in terms of energy? Do we know how much electric energy it consumes?
Today we see power cuts in our cities and energy sources like petrol and diesel’s prices are moving out of normal man’s reach. Seeing all these things do we ever think about saving energy while using computers? In this article I have put some information which can help you in saving energy.
Our Desktop computer uses about 60 – 250 watts of power where as some other computers use more. With most devices we can look at the label to see how much energy it can consume. Each part in computer accounts for different level of energy consumption. So architecture of computer will determine the power consumed by that system.
How much power computer used to consume in earlier days? The first electronic computer was invented in 1946. Since then lot of changes have occurred in the architecture and organization (material which they are made of) of computers and hence the power consumption by the computers. Earlier computers were using vacuum tubes and it consumed power of the order of several kilowatts ie thousands of watts. The ENIAC computer could perform 5000 arithmetic calculations per second, weighing 30 tons, containing 18000 vacuum tubes, consuming 150 kilowatts of power. EDVAC consumed 50kwatts. ORDVAC consumed 35 kwatts and UNIVAC-I consumed 124.5 kwatts on an average (these are all earlier computers). The power is dissipated both by the action of the switching devices contained in the CPU (such as transistors or vacuum tubes) as well as energy lost in the form of heat due to the resistivity of the electrical circuits.
Computer organisation and architecture - a major factor in power consumption Do you know microcontrollers? These microcontrollers are used in embeded technology like robotics etc. Once I asked one of my friends working in the field of embeded systems: “can we replace microprocessors with the micro controller in PC’s?”. He told many reasons and one of them was if we use microcontroller of microprocessor capacity, it will burst whole PC(personnal computer). Because power consumed by it and hence the heat produced by it will be more. So architecture and organisation of computers and its implementation has a major role in saving energy.
In earlier days the CPU component was accounted for most of the power consumed. Now a day, majority of the computer’s energy is consumed by monitors.
CPU But today we have CPUs like Intel XScale that can consume only 0.5 watts of power. We are able to find CPUs consuming power in the range 9-125 watts of power. If we are using a mobile (Motorola) it uses only 3 watts when we are on call and 2 watts when idle. AMD 64 FX a multicore processor uses about 125 watts.
MonitorIf some one wants to buy a computer he will first see speed of processor, then memory requirements (both primary and secondary) and then he goes for the monitor. Different varieties of monitors are coming in the market. Conventional computer systems have used cathode ray tube (CRT) technology for the computer display. However, in the past decade technological advances in Thin Film Transistor (TFT) Liquid Crystal Displays (LCD) have made this increasingly popular. Do you know why? There are many reasons and one of them is power saving.
DO LCDs save energy? Yes. LCDs use considerably less energy than CRTs, both when running and also when in standby mode. Overall, LCDs can reduce display energy use by some 60%. For
example, a 15” LCD uses around 25 watts when operational and around 3 watts when in
standby mode, compared with an equivalent viewing area 17” CRT that uses 80 watts when operational and 5 watts in standby mode. LCD screens recover from standby faster
than CRTs and consume less power when they do this. LCDs do not emit the same
heat load as does a CRT , and this saves energy on air conditioning in a building. The uniform brightness of an LCD screen means that the screen can better tolerate variations in light levels, and reductions in lighting also saves energy.
A Japanese study in the beginning of 2003 estimates that if Japan continues on its path towards replacing old CRTs with new LCDs so that some 76% of displays will be LCDs by the end of 2003, this will save 3 billion KWh of power consumption (the equivalent of the total power consumption of 1,000,000 households or the power production of about 3 nuclear power plants).
The Laptops and TFT monitors use this LCD technology. Our laptop uses about 15-45 watts only, that is very small compared to what CRTs consume.
What is LCD ? I think people have heard about LCD. Now a days, TV with LCD screen is very popular. LCD -- the name itself is little confusing. Liquid is completely different from crystal, then what is this Liquid Crystal!! They are neither liquid nor solid. Liquid crystals are closer to liquid state than solid. It takes fair amount of heat to change a suitable substance from solid into liquid crystal. It takes little more heat to convert into real liquid. They are very sensitive to temperature. It works on the principle of polarization. It is placed in between two polarized glasses.
Now a days TFT technology is used in LCD which will save more energy than earlier passive matrix LCD displays. The benefit of a TFT monitor is a separate, tiny transistor for each pixel on the display. Because each transistor is so small, the amount of charge needed to control it is also small. This allows for very fast re-drawing of the display, as the image is re-painted or refreshed several times per second. Since amount of charge needed to work is small, the power consumption is also less.
Here is some information about power consumption by some monitors.
Are we switching off monitor while not using it? Some people are used to sleep, listening to songs in computer. In such a situation they always forget to switch off the monitor. If we are copying something, suppose it takes lot of time and we are not doing anything else in computer, so better we switch off our monitor. It will save lot of energy. If we turn off monitor it will use only 0-10 watts of power.
Adjusting power settings on our computer to automatically go to standby/sleep mode after few minutes also saves energy. In sleep or standby mode it will use 1-6 watts of power. Here is some information about the power consumption by a monitor in different mode.
Apple iMac G5 w/built in 20" LCD screen.bmp)
This is all about how much the main components of computer consume power. Whether the power consumption depends on the tasks we do on computer? Processor intensive tasks and I/O intensive tasks consume more energy. Email and word processors consume less energy where as the computation done by ALU (Arithmetic Logic Unit) uses more. Copying of files from CDs and other I/O devices use more energy since it is related to memory.
Some people think that putting screen saver saves energy. But it is not true. It is recommended because it keeps CRT safe from damage. If you click refresh it will also consume energy.
This is all about importance of energy in computers. But computers account for only a fraction of worldwide electrical use, even with the burgeoning Internet usage. Air conditioning, lighting, refrigeration, etc. account for a lot more. In fact, as inefficient CRT monitors are being phased out in favor of newer LCD screens, energy consumption by computer is likely to remain flat or even go down over the next several years.
This article is published in our college magazene.