【正文】 ocoa Touch respectively. Layers of Core OS and Core Service are designed in C language to handle core system services, enabling developers to perform file access, sockets calling and data handling. CFNetwork and SQLite are also parts of these 2 layers. The layer of Media, according to its name, this layer is used to control video and audio, as well handle 2D and 3D images. The Open GLES Quratz part of the layer is coded with C language, while the part of CoreAudio and CoreAnimation is Objective C based. The layer of Cocoa Touch builds a basic framework for all kinds of programs in iPhone. Most programs run in Cocoa Touch layer, and it’s surely Objective C based [3] [4]. The latest iPhone OS is iOS 4. It includes the following new features: classification. This feature enables user to place sorted softwares into different documents, making it clearer to manage. 2. Email integration. One account is for all s from different providers. 3. iBook, originally from iPad, is built in iOS. 4. A brand new Apple Game Center makes iPhone a tremendous entertainment platform. . Android vs. iPhone Being the top 2 smart phone OSs, we’re sure that both Android and iPhone have their own advantages and disadvantages. Now let’s take a look at each of them, and see what unique feature they have. Android Froyo fully support multitask, which means you can listen to music while writing blog. And iOS 4, officially announced to be ‘multitasked’, is in fact a play of concept. Only a few of softwares which are authorized by Apple can run ‘simultaneously’, whose principle is much easier that multitask:when an application is switched out, its current state is saved and then the system just closes it. And when it’s switched in, we’re back to the previous snapshot [5] [6] [7]. During the publication of Android Froyo, Google announced it has ‘the most fluent web browser’,because the use of V8 JavaScript engine. V8 is a brand new engine, designed for running big size JavaScript application. In some kind 河北大學 21012 屆本科畢業(yè)生外文文獻翻譯 4 of tests, V8 is much faster than JScript from Inter Explorer, SpiderMonkey from Firefox and JavaScriptCore from Safari. It all owe to 3 key parts of V8, they’re fast attribute access, dynamic code generation, effective trash cleaning. . Fast Attribute Access JavaScript is a kind of dynamic language, which means attributes can be added or deleted at runtime, and they’re frequently changed. Most JavaScript engines use a dictionary style structure to store the attributes of an object, so it requires a whole dictionary search to find the position of attributes in ’s quite inefficient and it’s slower than Java and Smalltalk. To solve this problem, V8 discarded dynamic search and realized it in a different way: Create hidden classes for objects dynamically. In JavaScript, every time when we’re adding a new attribute to an object,we create a subclass with the new attribute from a hidden class as the super class. It’s a recursive course and the above performance happens only once when we first do this. Later we just use the previous hidden subclass when we’re in the same situation. So there’s no need to repeat operation and create a dictionary. This leads to the save of time and energy, as well make it easier for the implementation of class optimization and inner cache [4]. . Dynamic Code Generation When JavaScript is running for the very first time, V8 translate it directly into local machine code, rather than explain it to bytecode. Attribute access is done by inner cache, which is often translated into instructions by V8 at runtime. When it es to the code where certain object is accessed, V8 tries to find the current hidden class. Meanwhile, V8 assumes that all objects in the snippet are described by the same hidden class, so V8 willmodify corresponding inner cache to make the direct use of the hidden class more convenient. If thisassumption is correct, the access of attributes can be all done in only 1 instruction. Even if the predictionfails, inner cache is modified again by V8, which won’t take too muc h time and resource. When one hidden class is shared by a lot of objects, the access speed can be close to most dynamic language access speed. Inner cache and hidden class, mixed with dynamic code and class optimization, improve the efficiency of JavaScript at a large scale [4]. . Effective Trash Cleaning 河北大學 21012 屆本科畢業(yè)生外文文獻翻譯 5 V8 does memory recycles automatically. To guarantee the speed of object distribution, as well cut the time of trash cleaning and clear fragment up, V8 will interrupt the running application when performing trash cleaning. Mostly, only a small part of object stack is involved in trash cleaning cycle, so the interruption caused little. All location of objects and pointers are logged by V8, so the system won’t take object for pointer and memory overflow is avoided [4]. Besides ‘the most fluent web browser’, Google collaborated with Adobe and Android Froyo fully supports Flash. That’s to say, not only flash media, but all flash web pages can display perfectly on Android. To the contrary, Apple turned down Adobe and take HTML5 as iPhone’s web protocol, making it unable to show some flash based animation. Android Froyo also leads the way in work sharing. Smart phone with Froyo can be connected toa PC as a 3G NIC, and can also conveniently convert 3G signal to WiFi. iOS 4 can do the first too, butfailed to convert 3G to WiFi. Video conference is both supported by Froyo and iOS 4, but the conditions are different. You can see aFroyo user via camera as long as you get a camera also. However, iOS 4 user can only do video talk toanother iOS 4 user, which is a big limitation. While Android is ascendant in work interaction, Apple is unique in its friendship and added feature of ‘so