Loading of Operating system from secondary storage (HDD or SSD) to the main memory (RAM) is known as Booting or Boot up of computer system. The instructions to load up the OS (MAC, Linux or Windows) is stored on ROM. The booting process also includes POST i.e Power ON Self TEST.  After the operating system is loaded user can run Application and perform various tasks. The instructions to load the OS are stored in ROM (BIOS).

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