Step 1: When you turn on the computer or mobile device, the power supply or battery sends an electrical current to circuitry in the computer or mobile device. Step 2: The charge of electricity causes the processor chip to reset itself and finds the firmware that contains start-up instructions. Step 3: The start-up process executes a series of tests to check the various components. These tests vary depending on the type of computer or devices and can include checking the buses, system clock, adapter cards, RAM chips, mouse, keyboard, and drives. It also includes making sure that any peripheral devices are connected properly and operating correctly. If any problems are identified, the computer or device may beep, display error messages, or cease operating — depending on the severity of the problem. Step 4: If the tests are successful, the kernel of the operating system and other frequently used instructions load from the computer or mobile device's internal storage media to its memory (RAM). The kernel is the core of an operating system that manages memory and devices, maintains the internal clock, runs programs, and assigns the resources, such as devices, programs, apps, data, and information. The kernel is memory resident, which means it remains in memory while the computer or mobile device is running. Other parts of the operating system are nonresident; that is, nonresident instructions remain on a storage medium until they are needed, at which time they transfer into memory (RAM). Step 5: The operating system in memory takes control of the computer or mobile device and loads system configuration information. The operating system may verify that the person attempting to use the computer or mobile device is a legitimate user. Finally, the user interface appears on the screen, and any start-up applications, such as antivirus software, run.