Process, Types of OS

Process

·       A process is a program in execution

 Serial processing

·         There are two kinds of processing. Serial and Parallel.

·         In serial processing the CPU gets the info, analyze it, process it, send it as output and all these functions are done in a sequential manner, that is, only one job is done at a time and only on the completion of that job the other job starts. 
In parallel processing, all the above mentioned functions are done,as the name suggests, simultaneously or side-by-side.

·          This greatly reduces the time consumed for the operation though it might consume a lot of resource than serial processing.

Batch processing

 Similar jobs are grouped together and done (this saves time resource allocation and reallocation)

Multiprogramming

·         In multiprogramming system, when one program is waiting for I/O transfer; there is another program ready to utilize the CPU.

·         So it is possible for several jobs to share the time of the CPU.

·         But it is important to note that multiprogramming is not defined to be the execution of jobs at the same instance of time.

·         Rather it does mean that there are a number of jobs available to the CPU (placed in main memory) and a portion of one is executed then a segment of another and so on. A simple process of multiprogramming is shown in figure

                

 Types of OS

 1.Batch Operating Systems

 2.Multiprogramming OS

 3.Timesharing OS

 4.Real-Time Operating Systems

 5.Distributed OS

Batch OS

·       It uses batch processing

·       Program, data, and appropriate commands submitted together in the form of a job.

·       Batch OS usually allow little or no interaction b/w users and executing programs.

·       Batch processing has the greatest potential for resource utilization.

·       Scheduling of batch processing is in FIFO manner.

·       As memory management is concerned, it uses the same portion of the monitor for OS, and changing portion of the transient process, when one finishes other takes that area.

Example for batch processing: payroll, forecasting  etc.,

Multiprogramming OS  

·       Multiprogramming OS supports concurrent execution of programs.

·       Code and data of several programs are stored in memory resources are multiplexed among them.

·       Multi processing use multiple processors for concurrent processing.

Protection: Memory is protected from erroneous program corrupting the address.

 Example: Windows XP, Linux

 Timesharing systems 

·       Time-sharing is an example for multiprogramming OS. Multiuser system is another example of the time-sharing system. Here each user gets an illusion of getting an individual monitor. (It is made possible by allocating time slices, eg:  Round robin,)

Real-Time OS

·       A system is said to be Real Time if it is required to complete it’s work & deliver its services on time.

·       Example – Flight Control System

n All tasks in that system must execute on time.

·       Non Example – PC system

·        Uses priority-based preemptive scheduling

·       Purpose is to provide quick event response times.

Hard and Soft Real-Time Systems

n Hard Real-Time System   

w  Failure to meet deadlines is fatal

w  Example: Flight Control System

·       Soft Real-Time System

n Late completion of jobs is undesirable but not fatal.

n System performance degrades as more & more jobs miss deadlines

n Online Databases

   Some of the best known, most widely deployed, real-time operating systems are

·         LynxOS

·         OSE

·         QNX

·         RTLinux

·         VxWorks

·         Windows CE

 Distributed OS

·        A distributed computer system is a collection of autonomous computer systems capable of communication and cooperation via their hardware and software.

·        A distributed operating system is a software over a collection of independent, networked, communicating, and physically separate computational nodes

·         Each individual node holds a specific software subset of the global aggregate operating system. Each subset is a composite of two distinct service provisioners

·        The first is a ubiquitous minimal kernel, or microkernel, that directly controls that node’s hardware. Second is a higher-level collection of system management components that coordinate the node's individual and collaborative activities. These components abstract microkernel functions and support user applications

 Eg: Windows NT, Linux