* Batch processing
- Batch processing is a technique in which an Operating System collects the programs and data together in a batch before processing starts. An operating system does the following activities related to batch processing −
• The OS defines a job which has predefined sequence of commands, programs and data as a single unit.
• The OS keeps a number a jobs in memory and executes them without any manual information.
• Jobs are processed in the order of submission, i.e., first come first served fashion.
• When a job completes its execution, its memory is released and the output for the job gets copied into an output spool for later printing or processing.
Advantages
• Batch processing takes much of the work of the operator to the computer.
• Increased performance as a new job get started as soon as the previous job is finished, without any manual intervention.

Disadvantages
• Difficult to debug program.
• A job could enter an infinite loop.
• Due to lack of protection scheme, one batch job can affect pending jobs.

Offline Data Entry – A process of entering information in a specific database format as per the client’s requirements or instruction without using the internet is called offline data entry. The skills which are required in this process are typing, accuracy, and knowledge of Microsoft Word or Microsoft Excel. Usually, offline data entry tasks are assigned on the basis of contract, fixed or hourly rate.

Online Data Entry – This is totally different from offline data entry, here data entry tasks are accomplished by using internet services. The tasks involves in online data entry is submitting online forms, image processing, distinct submission of content in the website, data indexing, mining and cleansing, e-commerce product data entry, etc.

Data entry is a time-consuming process and it required a qualified staff. Hence, many companies outsource their online data entry tasks to process their business data in the substantial time frame.

Online processing is an automated way to enter and process data or reports continuously as use as the source documents are available. A good example of online processing is bar code scanning. When you buy a shirt at Target, the bar code gets scanned at the register. This shirt (source document) is immediately updated in Target’s inventory system as being sold. It is also updated in cost and sales reports. The online processing system continuously updates the entire accounting system.

What Does Online Processing Mean?
Before computers were widespread in business accounting systems, most companies had to process data or reports in batches. Invoices, for instances, had to be gathered, entered, and processed periodically by employees. Batch processing could be done daily or even weekly. As you can see, this is the most efficient manual way to process data, but it also provides outdated information. After computers and mainframe servers became more affordable for smaller business, most business moved from batch processing to online processing.

Example :- As you can see, the online processing system has many advantages over the batch processing system. Online processing is faster and gives continuous data for management. Take our Target example of instance. If batch processing was used, inventory reports would only be updated periodically. This means that management would only have useful inventory data on the day a batch process was run. This could be as often as every day or as infrequent as every month. Since online processing updates continuously, managers can run an inventory report any day at any time and have accurate up-to-date information.

Real Time Processing System
A real-time system is defined as a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment. The time taken by the system to respond to an input and display of required updated information is termed as the response time. So in this method, the response time is very less as compared to online processing.
Real-time systems are used when there are rigid time requirements on the operation of a processor or the flow of data and real-time systems can be used as a control device in a dedicated application. A real-time operating system must have well-defined, fixed time constraints, otherwise the system will fail. For example, Scientific experiments, medical imaging systems, industrial control systems, weapon systems, robots, air traffic control systems, etc.

There are two types of real-time operating systems.

Hard real-time systems
Hard real-time systems guarantee that critical tasks complete on time. In hard real-time systems, secondary storage is limited or missing and the data is stored in ROM. In these systems, virtual memory is almost never found.
Soft real-time systems
Soft real-time systems are less restrictive. A critical real-time task gets priority over other tasks and retains the priority until it completes. Soft real-time systems have limited utility than hard real-time systems. For example, multimedia, virtual reality, Advanced Scientific Projects like undersea exploration and planetary rovers, etc.

Time-sharing processing systems
Time-sharing is a technique which enables many people, located at various terminals, to use a particular computer system at the same time. Time-sharing or multitasking is a logical extension of multiprogramming. Processor's time which is shared among multiple users simultaneously is termed as time-sharing.
The main difference between Multiprogrammed Batch Systems and Time-Sharing Systems is that in case of multiprogrammed batch systems, the objective is to maximize processor use, whereas in Time-Sharing Systems, the objective is to minimize response time.
Multiple jobs are executed by the CPU by switching between them, but the switches occur so frequently. Thus, the user can receive an immediate response. For example, in a transaction processing, the processor executes each user program in a short burst or quantum of computation. That is, if n users are present, then each user can get a time quantum. When the user submits the command, the response time is in few seconds at most.
The operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time. Computer systems that were designed primarily as batch systems have been modified to time-sharing systems.

Advantages of Timesharing operating systems are as follows
• Provides the advantage of quick response.
• Avoids duplication of software.
• Reduces CPU idle time.

Disadvantages of Time-sharing operating systems are as follows 
• Problem of reliability.
• Question of security and integrity of user programs and data.
• Problem of data communication.