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A modern PC with a bus rate of around 1 GHz and a 32-bit bus might be 2000x or even 5000x faster, but might have many more gigabytes of memory. With boot times more of a concern now than in the 1980s, the 30- to 60-second memory test adds undesirable delay for a benefit of confidence that is not perceived to be worth that cost by most users.
Typically, the system firmware (UEFI or BIOS) will allow the user to configure a boot order. If the boot order is set to "first, the DVD drive; second, the hard disk drive", then the firmware will try to boot from the DVD drive, and if this fails (e.g. because there is no DVD in the drive), it will try to boot from the local hard disk drive.
On next boot, this image has to be made accessible before it can be loaded back into memory. To avoid having to hardcode handling for so many special cases into the kernel, an initial boot stage with a temporary root file-system – now dubbed early user space – is used. This root file-system can contain user-space helpers which do the ...
The BIOS uses the boot devices set in Nonvolatile BIOS memory , or, in the earliest PCs, DIP switches. The BIOS checks each device in order to see if it is bootable by attempting to load the first sector (boot sector). If the sector cannot be read, the BIOS proceeds to the next device.
The boot ROM of NXP systems on a chip (SOCs) support configuring the peripherals through specific pins of the system on a chip. On the i.MX6 family it also supports configuring the boot order through efuses. The boot ROM of several NXP SoCs have many ways to load the first stage bootloader (from eMMC, microSD, USB, etc.).
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.
The reset vector for MIPS32 processors is at virtual address 0xBFC00000, [11] which is located in the last 4 Mbytes of the KSEG1 non-cacheable region of memory. [12] The core enters kernel mode both at reset and when an exception is recognized, hence able to map the virtual address to physical address.
A modern PC is configured to attempt to boot from various devices in a certain order. If a computer is not booting from the device desired, such as the floppy drive, the user may have to enter the BIOS Setup function by pressing a special key when the computer is first turned on (such as Delete, F1, F2, F10 or F12), and then changing the boot order. [6]