Introduction to Operating System -Virtualization, Concurrency, and Persistence

 

How Operating Systems Really Work: Virtualization, Concurrency, and Persistence

Have you ever wondered how your laptop can play music, run a web browser, download files, and open a Word document—all at the same time—without melting down?
It might look simple, but beneath the surface, your operating system (OS) is doing incredibly sophisticated work.

In this , we’ll break down the three most important ideas that make modern operating systems possible:

• Virtualization

• Concurrency

• Persistence

These concepts are the foundation of how computers manage programs(applications), memory, and data. 

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1. Virtualization: Making One Computer Look Like Many

Virtualization is all about creating useful illusions.

You might have Spotify playing, Instagram open, and a browser loading—all on one phone.

It feels like all apps run simultaneously, but the phone is rapidly switching between them so smoothly you don’t notice.

Virtualization = making one CPU appear like many.

Even on a single physical CPU, the OS gives each running program the illusion that it has its own private processor.

This is exactly how the OS handles the CPU.

CPU Virtualization

Your computer might have only one CPU core, but the OS rotates between programs so quickly that every program feels like it has its own private processor.

The OS does this by:

• rapidly switching between programs

• saving each program’s progress

• deciding which program runs next (scheduling)

Memory Virtualization

The OS also gives each program its own private memory space—even though all programs share the same physical RAM.

It’s like dividing the pizza into slices so each person feels like they have their own pizza, even though there’s only one pizza.

Something even cooler happens with memory.
Each program gets its own private “virtual” address space, like its own private storage box.

This prevents programs from interfering with each other and keeps the system safe.

Under the hood:

• OS maps virtual addresses → physical memory

• Ensures protection and isolation

• Uses hardware support such as page tables

Virtualization makes a single machine behave like many smaller, simpler machines.

Overall Purpose of Virtualization

• Makes the system easy to use

• Provides a uniform programming interface

• Allows safe resource sharing

• Supports running many programs concurrently

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2. Concurrency: When Many Things Happen at Once

Concurrency is what happens when a system tries to do multiple tasks at the same time—or at least gives the illusion of doing so.It refers to problems that arise when multiple threads or processes run at the same time and share data or resources.

Why concurrency is tricky

Imagine two people using the same jar of coins.
If both try to:

1. pick up the jar

2. count the coins

3. put it back
   at the same time, they might mess up the count or overwrite each other’s results.

Computers face similar problems when multiple threads access the same data.

A real example

When two threads try to increment a shared counter variable

Because counter++ is not one action—it’s three smaller steps:

• load the value

• add 1

• store it back

If two threads interleave these steps, they can accidentally overwrite each other.

This is known as a race condition.

Why Concurrency Matters

• OS inherently operates concurrently:

  • servicing interrupts

  • switching between processes

  • handling I/O in parallel

• Modern applications also use threads to exploit multicore hardware.

How the OS helps

Operating systems provide tools to prevent these problems:

• locks

• semaphores

• atomic operations

All of these help coordinate access to shared data so programs behave correctly.

Concurrency makes systems fast and responsive—but only when managed carefully.

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3. Persistence: Making Data Last Forever

Everything in RAM disappears when the power goes off.
That’s why you lose unsaved work after a crash.

Persistence solves this problem.

What is persistence?

Persistence means storing data permanently on non-volatile devices like:

• hard drives

• SSDs

• flash storage

Your computer uses persistence when it:

• saves a document

• installs software

• stores photos

• remembers your settings

How the OS provides persistence

The OS uses a file system to organize and protect your data.
When you save a file, the OS:

1. finds a place on the disk

2. writes your data

3. updates metadata like file name and location

But writing to storage is slow and risky. So file systems use special techniques to ensure reliability, like:

• journaling

• copy-on-write

• careful write ordering

• Provide shared access:

  • Unlike CPU/memory, disks are not fully virtualized per-process because files are designed to be shared among programs (e.g., editor → compiler → executable workflow).

These methods keep your data safe, even if the system fails.

Key Challenges

• Reliability: avoid corruption after crashes

• Performance: storage devices are slow; OS must batch writes, buffer data, and schedule efficiently

Persistence ensures your files remain intact through crashes, shutdowns, and restarts.

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Bringing It All Together

Your operating system is constantly working behind the scenes to:

✔ Virtualize hardware

so each program feels like it has its own CPU and memory.

✔ Manage concurrency

so multiple tasks run smoothly—even when sharing resources.

✔ Provide persistence

so your files remain safe and accessible over time.

Together, these ideas form the backbone of modern computing.
Once you understand virtualization, concurrency, and persistence, the inner workings of your computer become much less mysterious—and a lot more impressive. 

Understanding these ideas makes it much easier to learn how systems work and prepares you for deeper courses in OS design, systems programming, and computer architecture.