diff between "system calls" and "kernel threads"

Hello,
May i know what is the difference between systems calls and kernel threads. I googled for the answer but as a newbie i didnt get understand what the difference?

Originally Posted by shariefbe Hello, May i know what is the difference between systems calls and kernel threads. I googled for the answer but as a newbie i didnt get understand what the difference?

They are two fundamentally different things:

1) A system call is a function call made from a program to a "system function" - these are functions like open() and sched_yield() that are specific to *nix (i.e. Windows would have different system calls).

2) A kernel thread is like a normal thread (i.e. independent thread of execution) except that it was spawned by a process in kernel-space.

i understand what is system call is. But still i am confused about threads.

Originally Posted by shariefbe i understand what is system call is. But still i am confused about threads.

Threads allow two diferent functions to execute at the same time.
Threads should be avoided when not necceray but used when you have to.

the question is not what is different between the two, but what, if any, the SIMILARITY is - what made you think there is any?

A system call is a request of some application in user space, requesting the services of the kernel to carry out a given task it doesn't have the right or privilege to do. The system call comes from user space, signals a trap into kernel space and then if approved carries out the service for the user mode app. So as an example, lets say we have a non modern Linux kernel and want to read out memory. Newer kernels disable this by default, but it can be re-enabled. We can read from /dev/mem, and doing so takes many read system calls, as the user space doesn't have access to /dev/mem. To see the system calls you can do something like this

sudo strace cat /dev/mem > /dev/null

A thread is the line of execution of a process. So lets say we create an application in C which is just a for loop that continually increments a variable by 1 to 1 million. The assembled version of that C app, will be numerous add instructions allowing the system to count to 1 million. All of those instructions are held in the processes thread of execution, and are executed one at a time. In older systems there was one thread per process, though in modern systems, each process can have as many threads as resources available. A process is just a program in execution by the way.