外文翻譯--分析和比較開放和封閉的移動平臺

1、.附 錄 An Analysis and Comparison of Open and Closed MobilePlatformsAndroid vs. iPhone1. IntroductionIn recent years, the popularity of smart phone kept going up. More and more smart phones are sold anda lot of people are embracing them. Smart phones brought great convenience to users, as well created

2、 opportunities for smart phone researchers. Thats to say, the wide spread of smart phones benefited both sides. At the same time, developing of smart phone OS becomes one of the smartest industry. To be a smart phone OS, the system should: 1. Provide services like a PC. 2. Work with a GPU for better

3、 visual effects. 3. Allow the user to surf on Internet freely. And apparently, therere also some weaknesses:1.Limited battery. 2. Poor CPU performance against PC CPU. 3. Small storage. 4. The use of RAM may leads to loss of data when the phone runs out of batteryNow the 2 giants of smart phone OS ar

4、e Android and iPhone OS. On one side, Android is based on Linux kernel and Dalvik virtual machine, and it is open sourced. The upper layer of Android is Java based,allowing developers to develop Android applications with Google SDK and sell their software in Android Market. On the other side, iPhone

5、 OS, which bases on Unix kernel and Darwin model but is closed sourced,evolves from Mac OS X and is the default OS of iPhone, iPod Touch and iPad. Objective C based software can run in iPhone OS, and just like Android, you can develop your own iPhone applications and upload them onto Apples App Stor

6、e for sale .By comparing the latest Android and iPhone OS, Android 2.2 Froyo and iOS 4, we can take a glimpse at the main feature of open and closed smart phone OSs. While the 2 OSs are designed in rather different mentality and functionality, its a little early to tell which one is better. 2. Smart

7、 Phone OS2.1. AndroidThe system architecture of Android consists of 5 layers, which are Linux Kernel, Android Runtime, Libraries, Application Framework and Applications, from bottom to top.Android provides core services like security, memory management, process management, network stack and drivers,

8、 basing on Linux 2.6. Being the abstract layer between software and hardware, the layer of Linux Kernel hides the implementing details of hardware and provides integrated services for upper layer.Dalvik virtual machine and Java core libraries are included in the layer of Android Runtime, providing m

9、ost functions in Java core libraries.The layer of Libraries contains a class of C/C+ libraries for Android components. Those libraries are integrated by the layer of Application Framework and then provided to developers.The layer of Application Framework provides all kinds of modules for program ini

10、tialization to simplify the use of components, allowing developers do whatever they want and provide services for other softwares, under the limitation of security, of course.Mainstream applications are located in the layer of Application, including e-mail, SMS, calendar, Google map, Web browser and

11、 contacts. Users interact directly with this layer12 .The latest version of Android, Android 2.2 Froyo, puts on some new features. They are: 1. Support Flash 10.1, enables user to watch flash on the phone. 2. V8 JavaScript engine in web browser leads to faster Internet data transportation. 3. Big ad

12、vance in network sharing. You can use the phone as a 3G NIC,or convert 3G signal to Wi-Fi. 4. Automatically software update. 5. Softwares can be setup in SD card to extend file storages.2.2. iPhoneiPhone OS is consist of 4 abstract layers: Core OS, Core Service, Media and Cocoa Touch respectively.La

13、yers 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 vi

14、deo and audio, as well handle 2D and 3D images. The Open GL-ES Quratz part of the layer is coded with C language, while the part of Core-Audio and Core-Animation 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 Tou

15、ch layer, and its surely Objective C based .The latest iPhone OS is iOS 4. It includes the following new features: 1.Software classification. Thisfeature enables user to place sorted softwares into different documents, making it clearer to manage. 2. Email integration. One account is for all e-mails

16、 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.2.3. Android vs. iPhoneBeing the top 2 smart phone OSs, were sure that both Android and iPhone have their own advantages and disadvantages. No

17、w lets take a look at each of them, and see what unique feature they have.Android 2.2 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 b

18、y 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 its switched in, were back to the previous snapshot .During the publication of Android 2.2 Froyo, Google announce

19、d 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 of tests, V8 is much faster than JScript from Internet Explorer, SpiderMonkey from Firefox and JavaScriptCore from Safari. It all

20、 owe to 3 key parts of V8, theyre fast attribute access, dynamic code generation, effective trash cleaning. 2.3.1. Fast Attribute AccessJavaScript is a kind of dynamic language, which means attributes can be added or deleted at runtime, and theyre frequently changed. Most JavaScript engines use a di

21、ctionary style structure to store the attributes of an object, so it requires a whole dictionary search to find the position of attributes in memory.Its quite inefficient and its slower than Java and Smalltalk.To solve this problem, V8 discarded dynamic search and realized it in a different way: Cre

22、ate hidden classes for objects dynamically. In JavaScript, every time when were adding a new attribute to an object,we create a subclass with the new attribute from a hidden class as the super class. Its a recursive course and the above performance happens only once when we first do this. Later we j

23、ust use the previous hidden subclass when were in the same situation. So theres 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 .2.3.2. Dynamic Code GenerationWhen Java

24、Script 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 comes to the code where certain object is accessed, V8 tries

25、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 don

26、e in only 1 instruction. Even if the predictionfails, inner cache is modified again by V8, which wont take too much 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 dy

27、namic code and class optimization, improve the efficiency of JavaScript at a large scale.2.3.3. Effective Trash CleaningV8 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 ap

28、plication 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 wont take object for pointer and memory overflow is avoided.Besides the mos

29、t fluent web browser, Google collaborated with Adobe and Android 2.2 Froyo fully supports Flash. Thats 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 iPhones web protocol, making it unable to show som

30、e flash based animation.Android 2.2 Froyo also leads the way in network sharing. Smart phone with Froyo can be connected toa PC as a 3G NIC, and can also conveniently convert 3G signal to Wi-Fi. iOS 4 can do the first too, butfailed to convert 3G to Wi-Fi.Video conference is both supported by Froyo

31、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 network interaction, Apple is unique in its friendship and entert

32、ainment.The added feature of software classification enables user to place sorted softwares into differentdocuments, making it clearer to manage. Whats more, therere hundreds of thousands applications inApp Store, meaning that iPhone can have up to hundreds of thousands functions. This is a ratherre

33、markable feature that Apple publicizes.And the most convincing point given by Apple, is that Android looks exactly familiar with iPhone. Although its just a subjective sense, the born of iPhone really brought big revolution to the phone industry, and the name Apple itself is a world famous brand . 3

34、. Open and Closed platforms3.1. SDKThe most important part of every developing platform is SDK, enable 3rd party developers to make software for the platform. Usually, libraries, debug tools and emulators are included in SDK. Different platforms distribute their SDKs differently. Some SDK is complet

35、e free and open, while others are strictly limited.Developers of open platforms can get and modify part or all of the source code. Google and Linux are leaders of open platforms; they publicized the whole source code of Android and Linux. The good point is that, platform owners can save a great amou

36、nt of time and energy developing and maintaining the platform, because 3rd party developers will do this for them. With less money spent on development and maintenance, a relatively low price can attract more and more phone users.Contrarily, closed platforms lock their source code in the safety and

37、forbid 3rd party accesses. Apple and Microsoft are the representatives of them, they are both closed sourced, but some differences do exists. 3rd party iPhone applications are restricted within narrow limits, for that Apple will look through every application which is uploaded onto App Store, and a

38、lot of applications are turned down.Microsoft dont check Windows applications at all, it all depends on the users themselves. You installed the mareware, you suffer the loss.3.2. Application MarketMarket is the medium between developers and users, hence its very important. Some predicted that there

39、will be more and more application markets while some dont think so. In current markets, both do exist. Some specify only one market for their products, while others sell their softwares in various markets.Softwares from Nokia, Microsoft and Linux Mobile are sold in every market. Developers of these

40、platforms can release their own application in whatever markets, so markets have to compete with each other for a living. This is good for users. However, the lack of universal management may lead to mess and chaos, softwares that have the same functionality exist in different markets, which confuse

41、s users a lot.Correspondingly, sole markets claim that most applications should be sold in them. This kind of monopolization leads to no competitor. App Store and Android Market are deputy of sole markets. Normally, iPhone applications can only be found in App Store, and Apple will check every one o

42、f them by itself. Good news is that every application in App Store is officially tested, its safe; Bad news is that a lot of pretty good softwares are rejected for various reasons. And a big unofficial mechanism is built by hackers, that is jailbreak and SIM unlock.Jailbreak is a process that allows

43、 iPad, iPhone and iPod Touch users to gain root access and unlock the operating system thus removing any limitations imposed upon them by Apple. Once jailbroken, iPhone users are able to download many extensions and themes previously unavailable through the App Store via installers such as Cydia. A

44、jailbroken iPad, iPhone or iPod Touch is still able to use the App Store and iTunes.And a SIM lock is a capability built into GSM phones by mobile phone manufacturers. Networkproviders use this capability to restrict the use of these phones to specific countries and network providers.Generally, phon

45、es can be locked to accept only SIM cards based on the International Mobile Subscriber Identity. SIM unlock make it possible to use a mobile phone without considering countries and networks specified by mobile phone manufacturers.However in Android, Google doesnt test every application at all, so al

46、though theres an official market for Android applications, you can still release your product anywhere you want. Considering security problems, Google banned the use of some components. Like jailbreak and SIM unlock in iPhone, root in Android gives users 100% control of their devices, along with som

47、e security risks. Root is a process that allows users of cellphones running the Android operating system to attain privileged control (known as "root access") within Android's Linux subsystem, similar to jailbreaking on Apple devices running the iOS operating system, overcoming limitat

48、ions that the carriers and manufacturers put on such phones. Rooting makes it possible to use custom versions of the Android system such as CyanogenMod, supporting features unavailable in stock ROMs. It also allows for newer versions of Android not supplied by the original device manufacturer. In co

49、ntrast to iOS jailbreaking, rooting is not needed to run applications not distributed by the official Android Market. It is needed however, when trying to access paid Android applications from countries which are not part of the paid applications market.3.3. IntegrationSome companies focus only on t

50、heir core industry, i.e. develop an operating system and provide an environment for 3rd party development. Others not only do these, but manage the process of developing a software to publicizing it. Depending on the integration of platforms, we sort them to 4 kinds: full integration platform, marke

51、t integration platform, device integration platform and no integration platform.The publicizing model of full integration platform is very strict. Its management ranges from device manufacturing to application release, whose representative is Apple. Apples factory produces iPhone, Apples App Store s

52、ells application, Apples iTunes is the channel of Apples resources. The whole process is under Apples control.Market integration platforms commit themselves to developing and selling softwares. Google is one of them. Unlike apple, Google dont have a factory to manufacture its own handsets, but only

53、developed Android and set up Android Market for Android applications. However, companies like Google definitely have the capability to produce its own devices. Google is in good relationship with HTC, who is the OEM of T-Mobile, O2 and Orange, etc.Device integration platforms produce their own hands

54、ets, but dont set up application markets. Forexample, RIM makes Blackberry, but theres no official application market for Blackberry. No integration platforms do few things. Microsoft neither makes mobile phones, nor sets up a market.What they do is only developing the operating system: Windows Phon

55、e 7. 4. ConclusionRepresentatives of open and closed platforms, Android 2.2 Froyo and iOS 4 are both loved and hated.Great browsers are built into them, and their producers are both world famous revolutionary. Android leans to Internet experience, which comes down in one continuous line with Google.

56、 But currently, various versions of Android fill the market, and most companies in Open Handset Alliance tend to customize their own Android systems. These facts make Android lack of a general brand image, so people may feel confused and say No to Android. iPhone OS focuses more on entertainment and

57、 its very friendly. But Apple is too cool to attract more customers: Diehard fans of Steve Jobs buy every product made by Apple, and people who dislike the style Apple do things may just sniffed at Apple.Besides, Android 2.2 Froyo succeeds the features of open platforms well. Its a users only platfo

58、rm, because users of Froyo can almost customize everything they want. And members of Open HandsetAlliance tend to provide more choices for users. And iOS 4, typically closed platform member, manages everything ranging from OS development to device manufacturing. Its a consider for users platform.To some extent, users of Android canonizes free and open, what they care is if they have 100% management of their handsets, no matter whether the OS is called Android or Another. Apple users are loyal to the brand;