Monitor, Short Term Scheduler, Distributed OS, Android OS

Q.7) Write short notes (Any Three)

i) Monitor
ii) Short Term Scheduler
iii) Distributed OS
iv) Android OS

i) Monitor

Monitor is an abstract data type that contains

- Shared data.
- A set of atomic operations on that data.
- A set of condition variables.

A function defined within a monitor can access only those variables declared locally within the monitor and its formal parameters. While using monitor, only one process is active at a time.

The operations in monitor are wait and signal. These operations are invoked by condition variable. The operation x.wait();means that the process invoking this operation is suspended until another process invokes x.signal(); where x is a conditional variable.



ii) Short Term Scheduler

Ans.

There are three types of scheduler in operating system.

- Long Term Scheduler
- Medium Term Scheduler
- Short Term Scheduler

It is also called CPU scheduler because it provides the processes to CPU.Processes that are ready to execute are available in ready queue. Short Term scheduler picks the process from ready queue and make available to CPU for execution. If there are more than processes in ready queue, then it picks the process with highest priority.Short Term scheduler is fastest among all other scheduler. It will invoke when some event is occur so the current running process is interrupted. For example clock interrupts, I/O interrupts, operating system calls, etc.

iii) Distributed OS

A distributed operating system is software that is distributed over a collection of independent nodes. These nodes are loosely coupled and communicating with each other. By loosely coupled systems means that such computers have no hardware connections at the CPU level. Each individual node contains specific software that is part of global OS. When a user works on distributed OS, it works in similar manner as a single node. It means, at actual it consists of multiple nodes, but appears to users as a single-node.

Distributed systems provide the following advantages:

- Sharing of resources.
- Reliability.
- Communication.
- Computation speedup

Distributed systems are more reliable than a central system because if any component in central system as example CPU, disk or memory fails, the system will go down.When there are multiple instances, the system will work continuously in spite of failures. Distributed systems handles both hardware and software errors.

A distributed system is a set of computers that communicate and co-operate each other using software and hardware interconnecting components.

iv) Android OS

Android is an operating system that was founded in Palo Alto of California, U.S. by Andy Rubin, Rich miner, Nick sears and Chris White in 2003. Later Android Inc. was acquired by Google in 2005. It is based on Linux family of operating system and mainly designed for smart phones. It is written in C, C++, and java language. Most of the android apps are developed in java programming language. Android operating system uses less memory to keep power consumption at a minimum, in contrast to desktop operating systems

Features of Android

- Integrated Browser
- Optimized Graphics
- Multi-touch
- Multitasking
- Bluetooth
- Streaming media support
- SQLite Database

Android operating system is the collection of software and can be divided in five sections.

- Linux kernel
- Libraries
- Android Runtime
- Application Framework
- Application

Linux kernel

It is available at the bottom of the Android software stack. It provides an abstraction between the device hardware and the upper layers. It provides the following functions in the Android system:

- Hardware Abstraction
- Memory Management
- Security Settings
- Power Management
- Support for Shared Libraries

Libraries

The next layer in the Android architecture includes Android’s native libraries. It is the collection of predefined API. User can directly reference these libraries while developing the apps.

Android Runtime

Android runtime includes the core java libraries andDalvik VM. It responsible for running apps on Android devices.Dalvik VM is optimized for low memory requirements.

Application Framework

There are so many important components are available in this layer and Our applications directly interact with these components.

Important blocks of Application Framework:

- Activity Manager
- Content Providers
- Telephony Manager
- Location Manager
- Resource Manager

Application

All the user defined applications are installed on this layer (Top of the layer).User directly interacts directly with this layer. This layer also comprises many native applications such as web browser email applications, SMS client app, Contact manager etc.