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Improve structure of BIOS section

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Philipp Oppermann
2020-10-11 23:22:26 +02:00
parent 4ec30d4624
commit 75a1d19b93
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blog/content/edition-2/posts/02-minimal-rust-kernel/index.md
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@@ -35,10 +35,10 @@ On x86, there are two firmware standards: the “Basic Input/Output System“ (*
Currently, we only provide BIOS support, but support for UEFI is planned, too. If you'd like to help us with this, check out the [Github issue](https://github.com/phil-opp/blog_os/issues/349).
### BIOS Boot
### BIOS
Almost all x86 systems have support for BIOS booting, including newer UEFI-based machines that use an emulated BIOS. This is great, because you can use the same boot logic across all machines from the last centuries. But this wide compatibility is at the same time the biggest disadvantage of BIOS booting, because it means that the CPU is put into a 16-bit compatibility mode called [real mode] before booting so that archaic bootloaders from the 1980s would still work.
But let's start from the beginning:
#### BIOS Boot Process
When you turn on a computer, it loads the BIOS from some special flash memory located on the motherboard. The BIOS runs self test and initialization routines of the hardware, then it looks for bootable disks. If it finds one, the control is transferred to its _bootloader_, which is a 512-byte portion of executable code stored at the disk's beginning. Most bootloaders are larger than 512 bytes, so bootloaders are commonly split into a small first stage, which fits into 512 bytes, and a second stage, which is subsequently loaded by the first stage.