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ProcessvsThread

What is the difference between a process and a thread?

Updated September 30, 20262 min read7 differences

In short

A process is a running program with its own memory, while threads run inside a process and share its memory: lighter, but harder to coordinate safely.

Operating Systemsp. 23

Process

A process is a running instance of a program, with its own memory space, resources, and at least one thread of execution managed by the operating system.

Read the page on Process

Operating Systemsp. 33

Thread

A thread is the smallest unit of execution an operating system can schedule, running inside a process and sharing that process's memory with other threads.

Read the page on Thread

Process and Thread compared

Aspect	Process	Thread
Definition	A running program with its own resources	A path of execution inside a process
Memory	Separate, isolated address space	Shares the process's memory with other threads
Creation cost	Heavier: a new address space and resources	Lighter: mainly a stack and registers
Context switch	Slower, because the memory mapping changes	Faster within the same process
Communication	Pipes, sockets, message queues, shared memory	Directly through shared variables
Failure impact	A crash usually stays inside that process	A crash can bring down the whole process
Main risk	Overhead and slower data exchange	Race conditions and deadlocks

The difference, explained

A process is an instance of a running program: the operating system gives it its own virtual address space, open files and other resources. A thread is a sequence of instructions that the CPU schedules; every process starts with one thread and can create more, all running inside the same process.

The essential difference is memory sharing. Processes are isolated, so one crashing or misbehaving rarely affects another, but they need explicit mechanisms such as pipes, sockets or shared memory to communicate. Threads share the process's heap and global variables, so they can exchange data instantly and are cheaper to create and switch between, but they need locks or other synchronization to avoid race conditions.

Real applications mix both. A web browser runs sites in separate processes for security and stability, while each of those processes uses many threads for rendering, networking and scripts. Servers often run several worker processes, roughly one per CPU core, each handling requests with a pool of threads or an event loop.

A common misconception is that more threads always mean more speed. Threads only run truly in parallel on multiple cores, and in some runtimes, such as the default build of CPython, a global lock lets only one thread run Python code at a time. Too many threads also waste time on context switching and on waiting for shared locks.

Which one should you use?

Choose Process when…

Tasks must be isolated so one failure can't bring down the others.
You need a security boundary, such as for running untrusted code.
CPU-heavy work must run in parallel in a runtime with a global lock.

Choose Thread when…

Tasks need to share a lot of data quickly.
You want lightweight concurrency for many I/O-bound tasks.
You need to keep a user interface responsive during background work.

Separate memory vs shared memory

Processpython

from multiprocessing import Process
counter = 0

def work():
    global counter
    counter += 1  # changes the child process's own copy

if __name__ == "__main__":
    p = Process(target=work)
    p.start()
    p.join()
    print(counter)  # 0: the child had its own memory

Threadpython

from threading import Thread
counter = 0

def work():
    global counter
    counter += 1  # changes the variable all threads share

t = Thread(target=work)
t.start()
t.join()
print(counter)  # 1: threads share the process's memory

Readers ask

Can a process have multiple threads?

Yes. Every process starts with one thread, the main thread, and can create more that run concurrently and share the process's memory.

Are threads faster than processes?

Threads are faster to create and to exchange data, because they share memory. Processes can still be the better choice for CPU-bound work in runtimes with a global lock, or when isolation matters.

What happens to threads when a process ends?

They all stop. Threads live inside their process, so when the process exits or crashes, every thread in it ends too.