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In computing, booting is the process of starting a computer as initiated via hardware such as a physical button on the computer or by a software command. After it is switched on, a computer's central processing unit (CPU) has no software in its main memory , so some process must load software into memory before it can be executed.
An initramfs-style boot is similar, but not identical to the described initrd boot. At this point, with interrupts enabled, the scheduler can take control of the overall management of the system, to provide pre-emptive multi-tasking, and the init process is left to continue booting the user environment in user space.
Once all the boot and system drivers have been loaded, the kernel starts the session manager (smss.exe), which begins the login process. After the user has successfully logged into the machine, winlogon applies User and Computer Group Policy setting and runs startup programs declared in the Windows Registry and in "Startup" folders. [5]
In x86 computers, a first-stage bootloader is a compact 512-byte program that resides in the master boot record (MBR) and executes when a computer starts. Running in 16-bit real mode at address 0x7C00, it performs minimal hardware initialization, sets up a basic execution environment, and locates the second-stage bootloader.
The boot ROM is either placed on the same die as the CPU or is an external ROM chip. On modern systems, the boot ROM (whether integrated into CPU or external ROM chip) is usually use NOR flash which supports execute in place. The boot ROM will then initialize the hardware busses and peripherals needed to boot.
When interrupt 19h is called, the BIOS attempts to locate boot loader software on a "boot device", such as a hard disk, a floppy disk, CD, or DVD. It loads and executes the first boot software it finds, giving it control of the PC. [28] The BIOS uses the boot devices set in Nonvolatile BIOS memory , or, in the earliest PCs, DIP switches.
This category is for articles about booting, the process of starting a computer from scratch and loading an operating system. The term booting is a shortened form of term bootstrapping . Subcategories
Cold start (or cold boot) may also refer to a booting process of a single computer (or virtual machine). [2] In this case services and other startup applications are executed after reboot. The system is typically made available to the user even though startup operations are still performed and slow down other operations.