Each process is given a contiguous 32 or 64-bit address space, bound by the architecture and unique to that process. This abstracted view of memory is called virtual memory and is achieved by the kernel's memory manager in coordination with the CPU's MMU. Virtual address space creates an illusion that every process exclusively owns the whole memory while executing. Virtual address space is the process' view of memory it is how the running program views the memory. To address this issue, the kernel provides a level of abstraction between the process and the physical memory called virtual address space. With multiple processes contending and executing simultaneously ( multi-tasking), the operating system must ensure that the memory allocation of every process is protected from accidental access by another process. Operating systems thus must deal with allocating unique memory to all contending processes within the physical memory (often finite) and also ensure their reliable execution. Modern-day computing platforms are expected to handle a plethora of processes efficiently. The following figure represents the layout of processes in memory: For instance, for a web browser with multiple open tabs (running simultaneous browsing sessions), each tab is considered a process instance by the kernel, with unique memory allocations.

Multiple instances of the same program can exist with their respective memory allocations. Apart from code and data, a process is assigned additional memory regions called stack (for allocation of function call frames with auto variables and function arguments) and heap for dynamic allocations at runtime.

The transformation from a program to a process happens when the program (on disk) is fetched into memory for execution.Ī program’s binary image carries code (with all its binary instructions) and data (with all global data), which are mapped to distinct regions of memory with appropriate access permissions (read, write, and execute). Applications can run either as firmware in dedicated devices or as a 'process' in systems driven by system software (operating systems).Īt its core, a process is a running instance of a program in memory. In other words, computing systems exist to run diverse application programs. Every element that goes into a computing platform is intended to enable effective and efficient ways for running applications. Quintessentially, computing systems are designed, developed, and often tweaked for running user applications efficiently.

Linux thread kernel stack size