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boot/docs/mem_layout.md

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# Physical memory layout
## Low memory
| Type | Range | |
|----------|---------------------|-------------------------------------------------|
| Reserved | 0x000000 - 0x000400 | real-mode interrupt vector table |
| Reserved | 0x000400 - 0x000500 | bios data area |
| Usable | 0x000500 - 0x004000 | main stack |
| Usable | 0x004000 - 0x006a00 | globals |
| Usable | 0x006a00 - 0x007c00 | memory map |
| Usable | 0x007c00 - 0x007e00 | boot sector |
| Usable | 0x007e00 - 0x080000 | conventional usable memory |
| Reserved | 0x080000 - 0x0a0000 | extended bios data area (maximum possible size) |
| Reserved | 0x0a0000 - 0x0c0000 | video memory |
| Reserved | 0x0c0000 - 0x0c8000 | video bios |
| Reserved | 0x0c8000 - 0x0f0000 | bios expansions |
| Reserved | 0x0f0000 - 0x100000 | motherboard bios |
0x10000: stage 3
TODO: once we're in real mode, repurpose s2 and s3 for a stack
TODO: load s4 into a separate memory region