標題：嵌入式系統與通用計算機系統的區別
To understand what falls into the category of embedded computing ,it is instructive to note what is not a requirement for embedded
devices.Lifetimes of embedded devices are very different from the three-year obsolescence cycle of general-purpose machines.
Some devices are nearly disposable:the average Japanese cellular phone is replaced in less than one year. At the opposite extreme,
infrastructural devices such as telephone switches depreciate on a 30-year schedule.these lifetime differences have concrete effects
on upgradability and backward compatibility.Few embedded devices have upgrade requirements. For example,avid automotive
enthusiasts change the chips in their cars,but these are usually ROMS,not processors.Most consumer items(e.g,cellular phones and
pagers)are replaced,not upgraded.
Backward compatibility is seldom an embedded requirement,as software does not migrate from one device to another.
(An interesting exception is game consoles:to maintain compatibility ,later console chips must be capable of being exactly as fast as
the early versions despite changes in underlying process technology.in consoles,backward compatibility is often implemented by
putting a complete copy of the previous-generation console in one small corner of the next-generation die.)
Because many embedded designs need not be backward compatible with previous implementations,designers are free to switch
designs with each product generation.Consequently,there is less emphasis on the distinction between architecture and implementation
.if a new version of a chip is slightly incompatible but much better then its predecessors,designers may still be willing to use it.
Designers of embedded devices face more constraints than designers of general-purpose devices. Power,energy efficiency ,cost
,and physical dimensions usually have a much bigger in embedded systems.This is not to say that embedded devices are
more difficult to build than general-purpose devices;the latter tend to have high overall performance goals and huge compatibility
requirements.But the overall priorities and the balance among them are different for embedded devices.
翻譯：
首先為了瞭解哪些屬於嵌入式計算範疇，我們必須知道嵌入式裝置必須具備哪些特點。就裝置生命週期而言，嵌入式裝置與三年才更新一次的通用裝置存在很大的差異，有些甚至是一次性的。日本人平均不到一年的時間就更換一次手機。與之相反的是，一些基礎設定如電話交換機則工作30年。生命週期的不同將會對裝置的升級和後續相容性造成很大的影響。很少有嵌入式裝置有升級的必要。比如說，狂熱的汽車愛好者通常更換車的晶片是ROM，而不是處理器。大部分的消費產品(如手機，呼機)是被替換掉，而不是升級。
另一方面，向後相容同樣不是嵌入式裝置的必須，就像軟體不需要考慮向其他平臺移植一樣。【但是有個有趣的個例：遊戲機。為了保持可擴充套件性，不管基礎硬體上有什麼樣的改變，新的處理器必須能夠處理的和原有的一樣快;為了實現後續相容，則是將上一代的控制程式固化到新一代處理器的某個儲存區裡】因為許多的嵌入式產品不需要和以前的產品保持相容，所以設計者們可以隨心所欲的設計每一代產品。所以，架構和實現並沒有特別明顯的區別。比如有個最新的晶片與器件有些小小的不相容，但是比以往的效能要好上許多，設計者可能更願意使用它。
嵌入式裝置設計者們將會比通用裝置設計者面臨更多的束縛。電源，功耗，成本，大小。當然，這並不是說嵌入式裝置設計就比通用裝置設計要難；通用設計對整體效能和相容性有很高的要求。當然這些要求與嵌入式裝置有著很大的不同。