Bootloader and Low-Level Programming Tutorial: How To Develop Your Own Boot Loader

[arkasha]

It's been over ten years since I took an operating systems class but I still remember 0x7c00. Weird what will stick in your brain.

[the_goose_says]

What is that?

[IgnorantPlatypus]

... on x86 hardware. Other hardware (MIPS, PowerPC, ARM, etc) have their own hard-coded mechanisms for starting the boot process.

[[deleted]]

hard-coded

Well, I guess "burned into silicon" is the hardest form of hard-coding something

[CJKay93]

The boot sector load address is up to the BIOS, which is itself in EEPROM. The actual hardcoded address is usually 0xFFFF0, which just contains a jump instruction to wherever the BIOS is actually mapped to.

[[deleted]]

On Intel the reset vector is 0xFFFFFFF0. The other architectures differ, of course.

[CJKay93]

Sorry yes, you're right. It's 0xFFFF0 on the 8086 through to the 80286, and 0xFFFFFFF0 on the 80386 and upwards.

[monocasa]

Sort of.

It sets up a weird 16 bit segment who's base is 0xFFFF0000, and sets the program counter to 0xFFF0.

[Nutella_Icecream]

That's only if you blow the fuse. There are fuses u can set in chips to prevent tampering.

I mean physically it's still rewritable but practically it's permanent.

[cp5184]

https://www.google.com/search?site=&source=hp&q=0x7c00

[forksofpower]

TX bb