Linux operating system For other uses, see Kernel (disambiguation). "Kernel (computing)" redirects here. For other uses, see Kernel (disambiguation). "Kernel (computer science)" redirects here. It is not to be confused with Compute kernel, Kernel method, or Kernel (image processing). The kernel is a computer program at the core of a computer's operating system with complete control over everything in the system.[1] It is the "portion of the operating system code that is always resident in memory".[2] It facilitates interactions between hardware and software components. On most systems, it is one of the first programs loaded on startup (after the bootloader). It handles the rest of startup as well as input/output requests from software, translating them into data-processing instructions for the central processing unit. It handles memory and peripherals like keyboards, monitors, printers, and speakers. A kernel connects the application software to the hardware of a computer. The critical code of the kernel is usually loaded into a separate area of memory, which is protected from access by application programs or other, less critical parts of the operating system. The kernel performs its tasks, such as running processes, managing hardware devices such as the hard disk, and handling interrupts, in this protected kernel space. In contrast, application programs like browsers, word processors, or audio or video players use a separate area of memory, user space. This separation prevents user data and kernel data from interfering with each other and causing instability and slowness,[1] as well as preventing malfunctioning application programs from crashing the entire operating system. The kernel's interface is a low-level abstraction layer. When a process makes requests of the kernel, it is called a system call. Kernel designs differ in how they manage these system calls and resources. A monolithic kernel runs all the operating system instructions in the same address space for speed. A microkernel runs most processes in user space,[3] for modularity.[4] This central component of a computer system is responsible for running or executing programs. The kernel takes responsibility for deciding at any time which of the many running programs should be allocated to the processor or processors. Random-access memory (RAM) Random-access memory is used to store both program instructions and data.[note 1] Typically, both need to be present in memory in order for a program to execute. Often multiple programs will want access to memory, frequently demanding more memory than the computer has available. The kernel is responsible for deciding which memory each process can use, and determining what to do when not enough memory is available. Input/output (I/O) devices I/O devices include such peripherals as keyboards, mice, disk drives, printers, USB devices, network adapters, and display devices. The kernel allocates requests from applications to perform I/O to an appropriate device and provides convenient methods for using the device (typically abstracted to the point where the application does not need to know implementation details of the device).