# 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                                |

### Allocations

- 0x00500 - 0x04000: stage 1/2 stack
- 0x04000 - 0x06a00: globals
- 0x07c00 - 0x07e00: stage 1 text
- 0x07e00 - 0x08000: gpt partition header
- 0x08000 - 0x08200: stage 2 partition table entry
- 0x08200 - 0x0c000: stage 2 text, stage 3 stack
- 0x0e000          : gdt
- 0x10000          : stage 3 text

0x10000: stage 3

TODO: once we're in real mode, repurpose s2 for a stack
TODO: load s3 into a separate memory region

TODO: use some fixed known memory address for the GDT, rather than putting it in stage 2.
      That way, we can safely overwrite stage 2 once we're done with it.