Android Operating System

1. Android – Mobile OS
Case study 2

2. Silberschatz, Galvin, Gagne. Operating System Concepts Essentials. 8th
Edition.
ISBN: 978-0-470-88920-6
A. Tanenbaum. Modern Operating Systems. 3rd Edition.
ISBN: 0136006639
H. Al-Rayes. Studying Main Differences between Android & Linux
Operating Systems. Diyala University.
Android Developer Website. http://developer.android.com
Sources and extra reading

3.  History of Android
 Android design principles
 Android Architecture
 Memory Management
 Threads and Scheduling
 Android File System
 Security
 Programming Interface
Topics covered in this session

4. - What is android? Linux 2.6 based operating system for mobile
devices.
- Open source and released under Apache Licence (Carriers can modify
it before distributing).
- Google acquired android in 2005.
- Android 1.0 released 2008.
- In 2012 Android 4.2 released
- Improvements include support for new devices:
- Cameras
- Multi core CPU
- Barometer
- etc
History of Android

5.  Long battery life.
 Fast boot up.
 Fast response.
 Applications (Programming environment?)
 Security
 How do these differ from the needs of a desktop system?
 Consider how the above are met by the system design.
Design principles – What is required of a
mobile OS?

6.  Battery
 Touch screen
 Portable (Mobile CPU)
 More limited memory
 Fewer devices
Mobile hardware differences

7. Android Architecture
Source: http://developer.android.com/about/versions/index.html

8. Android Architecture
Source: http://developer.android.com/about/versions/index.html

9. Android Architecture
Source: http://developer.android.com/about/versions/index.html

10. Android Architecture
Source: http://developer.android.com/about/versions/index.html

11. Android Architecture
Source: http://developer.android.com/about/versions/index.html

12. Application life cycle

13.  Android uses it’s own virtual machine to manage application
memory.
 Dalvik VM allows multiple instances of VM to be running
efficiently in parallel.
Memory management

14.  Differences between mobile app cycle and desktop app
cycle?
 Key principles:
 Android does not usually kill an app, they keep running even after you switch,
but saves state
 Task killers?
 Android kills apps when memory usage too high.
 But saves it’s state for quick restart.
 Uses Linux’s time sliced scheduling policy based on priority
Process Management

15. Process Priorities
 Split into background and
foreground.
 What happens if UI thread is
starved?

16. Flash Hard Disk Drives
Random Access ~0.1ms 5-10ms
File fragment impact No Greatly impacted
Total power ½ to 1/3 of HDD Up to 15+ watts
Reliability Reliable Less reliable due to mechanical
parts
Write longevity Limited number of writes. Less of a problem
Capacity <=512GB Up to 4TB
Price $1.5 - 2.0 GB $0.10 - 0.20 GB
Disk I/O

17.  What needs storing? Consider a map application (Lat/long).
 Swapping to flash affecting life.
Why not use swapping?

18.  Supports multiple different file systems (based on Linux Kernel).
 Usually yaffs2/vfat/ext4, depending on device manufacturer.
 Partitions:
 /boot (Included android kernel)
 /system (Android GUI and pre-installed applications). – Read only
 /recovery (Backup)
 /data (User data)
 /cache (Frequently accessed data)
 /misc (Contains misc system settings in form of on/off switches)
 /sdcard (SD card)
Android File System

19.  Android seeks to be the most secure and usable operating system for
mobile platforms by re-purposing traditional operating system
security controls to:
 Protect user data
 Protect system resources (including the network)
 Provide application isolation
 To achieve these objectives, Android provides these key security
features:
 Robust security at the OS level through the Linux kernel
 Mandatory application sandbox for all applications
 Secure interprocess communication
 Application signing
 Application-defined and user-granted permissions
Security

20.  Assigns .unique user ID (UID) to each android application.
 Uses UNIX style file permissions due to different UIDs
 Ensures app A doesn’t read app B’s files.
 Ensures app A doesn’t exhaust B’s memory
 Ensures app A doesn’t exhaust B’s CPU usage
 Ensures app A doesn’t exhaust user Bs devices (GPS, BT)
 Linux kernel enforces security between applications
 Stops memory corruption errors causing vulnerabilities.
 Read only system partition
Security Continued

21.  Use of restricted APIs require
application permissions.
 Application Signing. Application
packages are signed to identify author
and prevent tampering. Some windows
7 system files are signed in a similar
way.
Security Continued

22.  Each program runs in it’s own VM.
 Need to understand an activities lifecycle.
 Make use of Android SDK
 Applications programmed in Java, with layouts coded in XML.
 Packaged as .apk files for delivery through Android store.
 Importance of file size + data usage.
Programming for Android