zoukankan      html  css  js  c++  java
  • Modern Operating System --- Power Management

    The first general-purpose electronic comuter, the ENIAC, had 18,000 vacuum tubes and

    consumed 140,000 watts of power. As a result, it ran up a non-trivial electricity bill. After

    the invention of the transistor, power usage dropped dramatiscally and the computer

    industry lost interest in power requirements. However, nowadays power management is

    back in the spotlight for several reasons, and the operating system is playing a role here.

    Let us start with desktop PCs. A desktop PC often has a 200-watt power supply (which is

    typically 85% efficient, that is, loses 15% of the incoming energy to heat). If 100 million

    of these machines are turned out at once worldwide, together they use 20,000 megawatts

    of electricity. This is the total output of 20 average-sized nuclear power plants. From an

    environment point of view, getting rid of 10 nuclear power plant (or an equivalent number

    of fossil fuel plants) is a big win and well worth pursuing.

    The other place where power is a big issue is on battery-powered computers, incluing notebooks,

    handhelds, and Webpads, among others. The heart of the problem is that the batteries can

    not hold enough charge to last very long, a few hours at most. Furthermore, despite massive

    research efforts by battery companies, computer companies, and consumer electronics 

    companies, progress is glacial. To an industry used to a doubling of performance every 18 

    months (Moore's Law), having no progress at all seems like a violation of the laws of physics,

    but that is the current situation. As a consequence, making computers use less energy so 

    existing batteries last longer is high on everyone's agenda. The operating system plays a major

    rule here, as we will see below.

    At the lowest level, hardware vendors are trying to make their electronics more energy efficient.

    Techniques used include reducing transistor size, employing dynamic voltage scaling, using low-swing

    and adiabatic buses, and similar technique. There are two general approaches to reducing energy

    consumption. The first one is for the operating system to turn off parts of the computer (mostly

    I/O devices) when they are not in use because a device that is off uses little or no energy. The

    second one is for the application program to use less energy, possibily degrading the quility of the

    user experience, in order to stretch out battery time. We will look at each of these approaches

    in turn, but first we will say a little bit about hardware design with respect to power usage.

  • 相关阅读:
    Jersey Politics
    网络流——最小费用最大流
    网络流——最大流Dinic算法
    【洛谷2756】飞行员配对方案问题(二分图匹配,网络流24题)
    状压dp入门
    2018九江市赛
    [CQOI2007]余数求和
    CSAPC2008 skyline
    [ZJOI2009]函数 题解
    由不定方程想到的——数论选讲
  • 原文地址:https://www.cnblogs.com/miaoyong/p/4886768.html
Copyright © 2011-2022 走看看