Android: Mobile os Vs Desktop os

Mobile os Vs Desk acme os humanoid was designed from the ground up as an operating system (OS) for quick devices. Its built-in application and storage-management systems were engineered with battery life as one of the virtu eachy critical concerns. The humanoid OS does not execute like a desktop operating system. On a desktop OS, like Windows, macintosh OS X, or Ubuntu Linux, the intentionr is responsible for closing programs in site to keep a reasonable amount of memory available. On mechanical man, this is not the event. The OS itself automatically removes programs from memory as memory is needed.The OS whitethorn also preload applications into memory which it thinks might soon be needed. Under the stumper of Google mechanical man The easiest way I move think of to visualize Androids organize is by imagining a house with five rooms The house represents Android in general. The rooms inside, however, represent the five key features in Androids social organization * A pplications * The Application mannequin * Libraries * AndroidRuntime * Linux Kernel. Now, imagine that each of these rooms remove a certain number of pot. Each person represents an element of that room. diametrical rooms hold different amounts of slew.Applications This first room is a doozy. Its people represent all the applications that you nonplus in Android. Games, SMS a calendar, maps, a browser, and your contacts. all told applications be written in Java ,so you offer cast up or take away as many of these as you like. The Application Framework As a fixer, youll have full acces to the APIs used by the core apps. Android is designed so that any application can publish its capabilities. In turn, anyotherapplication can use those capabilities, as well. It has some security constraints, as is expected, but still. Thats pretty awesome.Along with all that, you get a Content Provider (which allows apps to sh atomic number 18 information), a preference Manager (to help you w ith graphics, layout turn ons, and so on, a Notification Manager (which gives you those annoying spatial relation beeps and such), and an Acticity Manager (which manages the life cycle of your apps). all in all in all, when it comes to creating applications quickly and easily, Android has you covered. Well cover how to write an application in another article. So, you could ordinate that the people in this room atomic number 18 the managers and providers and etcetera Believe me, there are a LOT.Libraries Android has a set of core libraries off of which the applications cover. As always, developers can directly advance these. Some of the core libraries include FreeType, SQLite, LibWebCore, and SGL. Android Runtime You could say that the Android runtime room is pretty exclusive it only has two people the Dalvik Virtual Machine and the core libraries (am I getting on your nerves with this people thing yet? ). In Google Android, theres a likewisel called DX. What this does i s it executes sends in . dex format, which are specially for the Dalvik Virtual Machine.This format is also created for minimal memory footprints, which makes it type for cell phones. The Dalvik Virtual Machine is written so it can run fourfold prcesses quickly and smoothly. It relies on the Linux Kernel to do its magic. Well talk al well-nigh that right after this. Linux Kernel Lastly, we have the Linux Kernel. This little room contains the Keypad, WiFi, Camera, and etc. number one woods. The Linux Kernel holds all of Androids internal structure together. It uses Linux 2. 6, and also acts like an abstract entity layer between the hardware and the software. 6 FILE SYSTEM . 1 Storage media NAND Android uses the YAFFS flash file system, the first NAND honed Linux flash file system. For mobile devices, hard disks are too large in size, too fragile and consume too much power to be useful. In contrast, flash memory provides agile read access time and part kinetic shock resistanc e than hard disks. There are fundamentally two different types of flash memory based on their verbalism technique NOR and NAND. NOR is low niggardliness, offers slow writes and fast reads. NAND is low cost, high density and offers fast writes and slow reads.Embedded systems are increasingly using NAND flash for remembering and NOR for code and execution. Limitations Important limitations of NAND memory include closing erasure and memory wear. B tuck in erasure means that when erasing any memory the whole evade must be erased. NAND can be randomly accessed on a page basis during programming, but cannot offer arbitrary random access rewrite or erase during normal operation. To overcome this limitation, memory segments are marked to be removed or dirty. When the entire block is dirty, then it can be erased.Memory wear means that there are a limited number of erase-write cycles in the flash memory and at the end of its lifetime the data integrity of storage will deteriorate. fag o ut levelling techniques are used to uniformly use whole sections and to optimize the add up lifetime of the device. Bad block management (BBM) is also used to serve write verification and remapping to spare sectors in case of write failure. 6. 2 File system for NAND YAFFS YAFFS (Yet Another Flash File System) was developed by Toby Churchill Ltd (TCL) as a reliable filing system with fast boot time for their flash memory devices.They initially tried to change existing flash file systems such as JFFS (used importantly for NOR) to add NAND support, but it turned out that the slow boot time and push back consumption of existing flash file systems was unacceptable. This led them to develop a different flash file system especially for NAND according to its features and limitations to optimize accomplishance and ensure blueness. Upon completion YAFFS performed better than existing flash file systems and can still be used with NOR, even though it is was specifically designed for NAND. YAFFS is the first flash file system specifically designed for NAND flash.YAFFS includes the following features Journaling a log-structured file system, which makes it robust to possible power failures. line of reasoning that YAFFS requires some RAM to maintain the data structure for its log. Garbage prayer highly optimized and predictable garbage collection strategies that makes it high performance and settled on a lower floor hard writing. Collection is executed when set free space becomes low. get off memory requirement it has a lower memory footprint than most other logstructured flash file systems, so it is to a greater extent scalable. Flexibility it uses a more general definition of NAND flash, is highly configurable and can be customized to work with various flash devices, different geometries, different wrongful conduct correction options, caching options, etc. Portability although YAFFS was originally designed for use with Linux, its modular design make it una ccented and portable to many operating systems. The file-system-specific code was kept separate from the main YAFFS file system code. The YAFFS Direct Interface (YDI) can hook up to other filesystems by applying a wrapper layer. Robustness it is well time-tested and has been used in many products. Bad block handling and error correction mitigate the limitations of flash memory. We can conceptually treat YAFFS as an improved version of flash file system with following improvements 1. YAFFS uses less(prenominal) run-time RAM. 2. YAFFS garbage collection is simpler and faster. 3. YAFFS uses a whole page per file for headers and provides no compression. 4. YAFFS can be used on NOR but, will not perform very well. Therefore, partition size can be a guideline to choose between YAFFS and JFFS.For smaller partition sizes JFFS is better suited whereas for larger sizes YAFFS performs better. KERNAL MODIFICATIONS Android is based on the Linux, but does not use a standard Linux kernel. The k ernel enhancements of Android include alarm driver, ashmem (Android shared memory driver), binder driver(Inter-Process Communication Interface), power management, low memory killer, kernel debugger and logger. All these kernel enhancements have been contributed back to the open source community under the GNU Public License (GPL) 8. Here we list a drumhead of the most substantial components alarm driver provides timers to wake devices up from cessation * ashmem allows applications to share memory and manages the sharing in kernel levels. * binder driver facilitates inter-process communication since data can be shared by multiple applications through the use of shared memory. A supporter registered as an IPC service do not have to worry about different locomote because binder will handle, monitor and manage them. Binder also takes fearfulness of synchronization between processes. * Power management built on the top on standard Linux Power Management (PM) and take a more aggressi ve policy to manage and save power.Android is hailed as the first complete, open, and free mobile platform. Complete The designers took a comprehensive approach when they developed the Android platform. They began with a secure operating system and built a robust software framework on top that allows for rich application training opportunities. Open The Android platform is provided through open source licensing. Developers have unprecedented access to the handset features when developing applications. Free Android applications are free to develop. There are no licensing or royalty fees to develop on the platform.No required membership fees. No required testing fees. No required signing or certification fees. Android applications can be distributed and commercialized in a variety of ways. Android instead has its profess Linux power extension, Power Manager instead. The core power driver (Shown at the bottom of Figure 3 as Power) was added to the Linux kernel in dress to facilitat e this functionality. This module provides low level drivers in order to control the peripherals supported by the Power Manager. These peripherals currently include prove display and backlight, keyboard backlight and button backlight.Each peripherals power is controlled through the use of Wake Locks. These locks are requested through the API whenever an application requires one of the managed peripherals to remain powered on (Each lock setting shown in Table 1). If no wake lock exists which locks the device, then it is powered off to conserve battery life. In the case of multiple power settings the transition is managed through the use of delays based on system activity. A sample of this behaviour is shown in Figure 4 for the screen backlight. In addition to Wake Locks the Power.