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On the original IBM PC and XT, if no bootable disk was found, the BIOS would try to start ROM BASIC with the interrupt call to interrupt 18h. Since few programs used BASIC in ROM, clone PC makers left it out; then a computer that failed to boot from a disk would display "No ROM BASIC" and halt (in response to interrupt 18h).
Following the release of Windows 8 in late 2012, it was discovered that certain Lenovo computer models with Secure Boot had firmware that was hardcoded to allow only executables named "Windows Boot Manager" or "Red Hat Enterprise Linux" to load, regardless of any other setting. [184]
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]
A bootable MBR device is defined as one that can be read from, and where the last two bytes of the first sector contain the little-endian word AA55h, [nb 6] found as byte sequence 55h, AAh on disk (also known as the MBR boot signature), or where it is otherwise established that the code inside the sector is executable on x86 PCs.
The computer first executes a relatively small program stored in the boot ROM, which is read-only memory (ROM, and later EEPROM, NOR flash) along with some needed data, to initialize hardware devices such as CPU, motherboard, memory, storage and other I/O devices, to access the nonvolatile device (usually block device, e.g., NAND flash) or ...
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.
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When a system on a chip (SoC) enters suspend to RAM mode, in many cases, the processor is completely off while the RAM is put in self refresh mode. At resume, the boot ROM is executed again and many boot ROMs are able to detect that the SoC was in suspend to RAM and can resume by jumping directly to the kernel which then takes care of powering on again the peripherals which were off and ...