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cleaned up memory maps and added a map for stage2

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Elaina Claus
2025-09-13 12:48:19 -04:00
parent 7cd6baa74d
commit a50af35abd
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docs/Stevia Notes.md
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@@ -207,24 +207,45 @@ Each GDT entry is 8 bytes:
## **5. Memory Layout Example**
### **Low Memory (First MiB)**
### **Low Memory/Upper Memory map (<= 1MiB)**
| Start | End | Size | Type | Description |
|-------------|-------------|-----------------|-----------------------|----------------------------------|
| 0x00000000 | 0x000003FF | 1 KiB | RAM (partially unusable) | Real Mode IVT (Interrupt Vector Table) |
| 0x00000400 | 0x000004FF | 256 bytes | RAM (partially unusable) | BDA (BIOS data area) |
| 0x00000500 | 0x00007BFF | almost 30 KiB | RAM - free for use | Conventional memory |
| 0x00007C00 | 0x00007DFF | 512 bytes | RAM (partially unusable) | OS BootSector |
| 0x00007E00 | 0x0007FFFF | 480.5 KiB | RAM - free for use | Conventional memory |
| 0x00080000 | 0x0009FFFF | 128 KiB | RAM (partially unusable) | EBDA (Extended BIOS Data Area) |
| 0x000A0000 | 0x000FFFFF | 384 KiB | various (unusable) | Video memory, ROM Area |
| Start | End | Size | Type | Description |
|-------------|-------------|-----------------|----------------------|--------------------------------|
| 0x00000000 | 0x000003FF | 1 KiB | RAM reclaimable~1~ | Real Mode IVT |
| 0x00000400 | 0x000004FF | 256 bytes | RAM reclaimable~1~ | BDA |
| 0x00000500 | 0x00007BFF | 29 KiB + 767b | RAM - free | Conventional memory |
| 0x00007C00 | 0x00007DFF | 512 bytes | RAM reclaimable~2~ | OS BootSector |
| 0x00007E00 | 0x0007FFFF | 480.5 KiB | RAM - free | Conventional memory |
| 0x00080000 | 0x0009FFFF | 128 KiB | RAM (unusable)~1~ | EBDA (Extended BIOS Data Area) |
| 0x000A0000 | 0x000FFFFF | 384 KiB | Upper RAM (unusable) | Video memory, ROM Area |
### **Extended Memory (Above 1 MiB)**
1. Reclaimable in the event that you *never* need the BIOS again & once the CPU is in protected mode.
2. Reclaimable after you are done with with the MBR/VBR stages.
| Start | End | Size | Description |
|-------------|-------------|-----------------|------------------------|
| 0x00100000 | 0x00EFFFFF | 14 MiB | RAM - free for use |
### **Extended Memory (> 1 MiB)**
This is only an example, you should always check the memory map.
| Start | End | Size | Description |
|-------------|-------------|-----------------|---------------------------------------|
| 0x00100000 | 0x00EFFFFF | 14 MiB | RAM(?) - free for use |
| 0x00F00000 | 0x00FFFFFF | 1 MiB | Possible memory-mapped hardware (ISA) |
| 0x01000000 | ? | ? | More extended memory |
| 0x01000000 | ? | ? | More extended memory |
| 0xC0000000 | 0xFFFFFFFF | 1 GiB | Memory mapped PCI devices, BIOS, etc. |
| 0x0000000100000000 | ? | ? | RAM - usable in PAE/64-bit mode |
| 0x0000000100000000 | ? | ? | RAM(?) - usable in PAE/64-bit mode |
## **6. Stage2 Memory Layout **
Overall, Tiny (64 KiB page) Code/Data, Flat 4GiB mapping in gs/fs after unreal switch
| Start | End | Size (Bytes) | Type | Description |
|-------------|-------------|--------------|--------------------|----------------------------|
| 0x00000000 | 0x000003FF | 0x400 | RAM - (BIOS) | Real Mode IVT |
| 0x00000400 | 0x000004FF | 0x100 | RAM - (BIOS) | BDA |
| 0x00000500 | 0x000042FF | 0x3E00 | RAM - .text/.data | Code and constants/strings |
| 0x00004300 | 0x000044FF | 0x100 | RAM - .sign | EOF marker/signature |
| 0x00004500 | 0x000074FF | 0x3000 | RAM - bss | Runtime data/stack |
| 0x00007500 | 0x00007FFF | 0xB00 | RAM - reserved | Reserved |
| 0x00008000 | 0x0000DFFF | 0x6000 | RAM - heap | Conventional memory |
| 0x0000F000 | 0x0000FFFF | 0x1000 | RAM - reserved | Reserved |