The Holy Grail of mobile computing is a portable device that has the power of a desktop computer， lasts more than a day on a single battery charge， and weighs next to nothing. Right now， such a computer is still a myth.
But computer makers are pushing the limits of weight and power.
Today’s so-called ultra① light computers， which retail from about 1，800 to more than 3，000， are less than an inch thick， weigh less than three pounds， and have the computing power of a typical desktop.
Yet many of the smallest， lightest computers are studded with tradeoffs②. They， for example， won’t last more than a few hours on a single battery， don’t come with built-in CD or DVD drives， and have less powerful processors than “normal” PCs.
Right now， you have to compromise to get to the form factor， that is， the ideal size and weight. But we’re making plans to offset them.
One of the most promising new technologies to help achieve that goal is a new breed of low-powered microprocessors that can vary the speeds at which they operate.
During complex computing tasks -such as crunching③ a large amount of numerical data in a spreadsheet—the processors might run at their top rate， or “clock speed.” But for less demanding tasks—running a word processor or playing music， for instance—the chip can slow way down.
The chief advantage of these processors， including Intel’s Mobile Pentium III-M and Transmeta Corp.’s Crusoe， is the power they save. At slow speeds， for example， they typically require less than 1 watt， which means a computer’s rechargeable batteries will last much longer between charges. Meanwhile， labs are testing new battery technologies.
Most rechargeable batteries， made of lithium④， provide portable computers about four or five hours before they need to be recharged. But research into different， lighter materials—such as zinc⑤ combined with air—could produce batteries with greater “energy densities.” If more power can be packed into less space， portable computers can be made even lighter than the current crop of ultra lights.
Computer makers have touted a new type of portable computer called the tablet PC.
These computers—typically the size and shape of a 1.5-inch-thick stack of typing paper-feature a screen that users can “write” on using a plastic stylus⑥. The software， a special version of Microsoft’s new Windows XP operating system， can interpret those pen strokes. And， instead of using a computer mouse to click on icons⑦， users will merely tap on the screen to access the Internet or start programs.
Such pen-based computers will have all the power， memory and features of an ordinary notebook computer.
Such snazzy portables may not be as cheap as ordinary notebooks， however. Early tablet PCs were priced well above 3，000 because of expensive parts such as the touch-sensitive screen.
① ultraadj. 极端的，偏激的，过分的
② tradeoff=trade-off
③ crunchv. 嘎吱作响地咬嚼
④ lithiumn. ［化］锂
⑤ zincn. ［化］锌[U]
⑥ stylusn. 描画针
⑦ iconn. ［电脑］代表所指谓的图像
打造更好的超轻电脑
“圣盘”是一种便携式电脑，它的能力如同一台台式电脑，电池充电一次可用一天多，而且重量很轻。现在这样的电脑还只是个神话，但电脑制造者正在突破电脑重量和能力的极限。
现在，这种所谓超轻电脑零售价大约在1，800到3，000多美元，该电脑的厚度不到一英寸，重量不到3磅，其计算能力相当于一台普通的台式电脑。
然而，许多最小的最轻的电脑都是权衡利弊后的最佳组合。例如，它们一次充电电池的使用不能超过几个小时，不能匹配内置的CD或DVD驱动装置，处理器的能力低于 “正常”电脑。
电脑制造商不得不折衷设计方案，才能达到理想的大小和重量。但是要弥补因折衷而造成的不足使其有助于达到这一目标。最有希望的新技术之一就是制造新型的低功率微处理器，处理器在运行中可以改变速度。
在执行复杂的计算任务，如连续处理大批的数字数据时，这种处理器以极高的速度，即 “时钟脉冲速度”运行。但是在执行要求较低的任务，如运行一个文字处理器或放音乐时，该芯片能减速。
包括英特尔的便携式奔腾3-M和Transmeta公司的Crusoe在内的这些处理器的主要优点是节省功率。例如，在慢速时，它们一般只需不到1瓦特功率，这意味着该计算机的可充电电池在两次充电之间使用时间更长。与此同时，新的电池技术也正在试用。
大多数可充电电池是由锂制作的，它能为便携式电脑提供大约4或5小时电源，然后才需要再充电。如果研制出不同的、更轻的如锌与空气结合的材料，就能生产具有更大 “能量密度”的电池。如果能在更小空间中储存更大功率，便携式电脑就能造得比现在任何超轻电脑还要轻。
电脑制造商已推出了一款叫平板个人电脑的便携式电脑，这种电脑——一般只相当于1.5英寸打印纸的大小和形状——有一个用户可用塑料笔 “写”的视屏。内置的软件是微软新版视窗XP的一种特殊版，它可以翻译笔写的内容。使用者不再使用鼠标去点击图标，仅仅靠触摸视屏就可以上网或启动程序。
这种笔写式电脑具有普通笔记本电脑的运算能力、记忆和特征。
然而，这样时新的便携式电脑可能不如普通笔记本电脑便宜。因为像触敏视屏这样一些部件价格十分昂贵，最初平板电脑的售价远远超过3，000美元。