What is an Operating System?
An Operating System (OS) is the most important software that runs on a computer. It acts as an intermediary or a manager between the computer’s hardware and the user. 🤝
Think of an OS as the manager of a busy restaurant. The manager doesn’t cook the food (the hardware’s job) or eat the food (the user’s job), but they take orders, manage the kitchen staff, and ensure everything runs smoothly so the customer gets their meal.
In short, you cannot use a computer or a smartphone without an operating system.
- Examples: Microsoft Windows, macOS, Linux, Android, and iOS.
Main Functions of an Operating System
The OS is responsible for managing all the resources of the computer. Its key functions are:
- Process Management: Manages the execution of programs (processes). It decides which process gets the CPU and for how long.
- Memory Management: Manages the main memory (RAM). It allocates and deallocates memory space required by programs.
- File Management: Organizes and keeps track of files and directories on storage devices like hard disks.
- Device Management: Manages all input/output (I/O) devices like keyboards, mice, printers, and disk drives.
- Security: Provides security by means of passwords and other similar techniques to prevent unauthorized access to programs and data.
Types of Operating Systems
Different operating systems are designed for different purposes. Here are the most important types you should know for your exams.
1. Batch Operating System
This is one of the earliest types of OS. Here, similar jobs are batched together and executed as a group. The user does not interact directly with the computer.
- How it works: Users would prepare their jobs (on punch cards) and submit them to a computer operator. The operator would collect jobs with similar needs into a batch and run them together.
- Key Idea: Maximize CPU utilization by running jobs back-to-back.
- Example: Bank statement generation or payroll systems, where the same task (calculating salary) is performed for thousands of employees.
2. Multiprogramming Operating System
This OS keeps several jobs in the main memory at the same time. The CPU is never idle.
- How it works: When one job needs to wait for an I/O operation (like reading from a disk), the OS switches the CPU to another job that is ready to run.
- Key Idea: Increase CPU utilization by always having a job to execute.
- Example: Running a word processor and a web browser on your PC. While the word processor waits for your input, the OS can let the browser download a file.
3. Time-Sharing (or Multitasking) Operating System
This is a logical extension of multiprogramming. It allows many users to share the computer’s resources simultaneously. The CPU’s time is shared among multiple jobs.
- How it works: The system switches between processes so frequently (using a technique called time-slicing) that each user feels like they have their own dedicated computer.
- Key Idea: Provide good response time to each user.
- Example: Modern desktop operating systems like Windows 11 and macOS. You can have multiple applications open and actively running at once.
4. Real-Time Operating System (RTOS)
This OS is used where there are strict time requirements for operations. The system must process data and produce a result within a specified deadline.
- How it works: It is designed for high reliability and predictability.
- Key Idea: Completing a task on time is more important than anything else.
- Example: Systems used in missile guidance, medical imaging (like MRI machines), and industrial control systems where a delay could be catastrophic.
5. Distributed Operating System
This system runs on multiple, independent computers that are connected by a network but appears to the user as a single, coherent system.
- How it works: It manages a group of distinct computers and makes them work together.
- Key Idea: Increase reliability, performance, and resource sharing across a network.
- Example: A network of servers working together to manage a large banking application or a major e-commerce website.
Quick Comparison Table
| OS Type | Main Goal | Key Feature | Example |
| Batch | Maximize CPU use | Jobs with similar needs run in a group | Payroll System |
| Multiprogramming | Maximize CPU use | Keeps multiple jobs in memory | Early Mainframes |
| Time-Sharing | Minimize response time | CPU time is shared among users | Windows, macOS |
| Real-Time | Meet deadlines | Strict time constraints | Medical, Industrial Systems |
| Distributed | High reliability & sharing | Manages multiple computers as one | Networked Servers |