= Appendix 3. Memory Map

This is Appendix 3 of the [[SD-8516 Programmer's Reference Guide]].

== Memory Map
=== BANK 0 - User RAM & System Variables ($00,0000–$00,FFFF)

^ Address Range ^ Size ^ Name / Area ^ Description / Notes ^
| $000000–$00FFFF | 61,184 B | User RAM | General purpose free RAM |
| $000100–$00FF00 | ~64 KB | BASIC Program Area | Main BASIC program storage (see int0x05h.sda) |

**Total free in Bank 0:** ≈65,280 bytes

=== BANK 1 - KERNAL ROM & HARDWARE ($010000–$01FFFF)

^ Address Range ^ Size ^ Name / Symbol ^ Description / Notes ^
| $010000–$0100FF | 256 bytes | Kernal Bootstrap | Reserved for boot code |
| $010100–$013FFF | ~16 KB | Kernal Code | Main KERNAL routines + limited expansion space |
| $014000–$01DBFF | 40,960 bytes | RESERVED | Reserved for future KERNAL expansion |
| $01DB00–$01DBFF | 256 bytes | PATB_TBUF | ROM BASIC tokenizer scratch space (currently underused?) |
| $01DC00–$01DFFF | 1,024 bytes | Stack Space | Hardware stack (grows down from $01DFFF; overflow if SP < $01DC00) |
| $01E000–$01E7FF | 2,048 bytes | VM1_CHAR_ROM | PETSCII font data (copied from character ROM at initialization) |
| $01E800–$01E8FF | 256 bytes | Kernal Workspace | Reserved for KERNAL internal use |
| $01E900–$01EBFF | 768 bytes | INT_VECTOR_TABLE | Interrupt vector table (256 vectors × 3 bytes = 24-bit addresses, little-endian) |
| $01EC00–$01ECFF | 256 bytes | SCRATCH_BUFFER | General-purpose scratch space (used by INPUT, expression eval, parsing, etc.) |
| $01ED00–$01EDFF | 256 bytes | INPUT_BUFFER | Input line buffer (also used as part of PATB system variables) |
| $01EE00–$01EEFF | 256 bytes | PATB_VARIABLES + stacks etc. | PATB_BASIC variables, expression stack, GOSUB/FOR stacks, program pointers… |
| $01EF00–$01EF0B | 12 bytes | Video System Registers | VIDEO_MODE, VIDEO_COLUMNS, VIDEO_ROWS, VIDEO_CHAR_WIDTH/HEIGHT, VIDEO_CLOCK… |
| $01EF0C–$01EF0F | 4 bytes | Cursor System | CURSOR_BLINK, CURSOR_STATE, CURSOR_X, CURSOR_Y |
| $01EF10–$01EF31 | 34 bytes | Keyboard System | KBD_STATUS_FLAGS, KEYBOARD_COUNT, KEYBOARD_BUFFER (32 bytes) |
| $01EF32–$01EF3A | 9 bytes | Input/Syscall System | INPUT_MODE, INPUT_LENGTH, SYSCALL_STATUS/ADDR, KBPC (BASIC program counter) |
| $01EF3B–$01EF42 | 8 bytes | FREE | Reserved for future use |
| $01EF43–$01EF49 | 7 bytes | Extended Video System | VIDEO_COLOR_MODE, VIDEO_TEXT_BASE, VIDEO_COLOR_BASE |
| $01EF4A–$01EF7F | 54 bytes | FREE | Reserved for hardware expansion |
| $01EF80–$01EFBF | 64 bytes | Sound System (4 voices) | see: [[Appendix 5 Sound System|SD-450 Sound System]] |
| $01EFC0–$01EFFF | 64 bytes | FREE | Reserved for sound system expansion |
| $01F000–$01F3E7 | 1,000 bytes | VM1_TEXT_BASE | Video Mode 1 – 40×25 text character map |
| $01F3E8–$01F7FF | 1,048 bytes | FREE (text area) | — |
| $01F800–$01FBE7 | 1,000 bytes | VM1_COLOR_BASE | Video Mode 1 – 40×25 color attribute map |
| $01FBE8–$01FFFF | 1,048 bytes | FREE (color area) | — |

=== BANK 2 – USER RAM ($020000–$02FFFF)

^ Address Range ^ Size ^ Name / Area ^ Description ^
| $020000–$02FFFF | 65,536 B | User RAM | Completely free |

=== BANK 3 – USER RAM ($030000–$03FFFF)

^ Address Range ^ Size ^ Name / Area ^ Description ^
| $030000–$03FFFF ^ 65,536 B | User RAM | Completely free |

=== Quick Free Space Summary

^ Bank ^ Free Bytes ^ Notes ^
| 0 | 65,280 | Mostly user RAM + small BASIC area |
| 1 | ~40,960 | Reserved for future KERNAL expansion |
| 2 | 65,536 | Completely free |
| 3 | 65,536 | Completely free |
| **Total** | **237,312** | Available for user programs & data |