Acorn Atom/System Memory Map
                         ============================

+-----------+-------------------------------+-------------------------------+
|           | Acorn Atom                    | Acorn System                  |
+-----------+-------------------------------+-------------------------------+
|0000-03FF  | Low RAM                                                       |
| 0000-00FF |  Zero page                                                    |
| 0100-01FF |  OSCLI buffer, input buffer and 6502 stack                    |
| 0200-021F |  Vectors                                                      |
| 0220-023F |  Unused                                                       |
| 0240-02FF |  Atom BASIC workspace                                         |
| 0300-03FF |  Atom BASIC workspace                                         |
+-----------+-------------------------------+-------------------------------+
|0400-0FFF  | I/O devices                                                   |
| 0400-07FF |  Teletext screen RAM                                          |
| 0800-08FF |  Teletext 6845 controller                                     |
| 0900-09FF |                                                               |
| 0A00-0AFF |  8271 floppy disk controller                                  |
| 0B00-0BFF |                                                               |
| 0C00-0CFF |  Universal Interface card - 6522 VIA, 6850 ACIA, 8255 PIO     |
| 0D00-0DFF |                                                               |
| 0E00-0EFF |  8154 PIO/RAM 1 (keyboard/LED control)                        |
| 0F00-0FFF |  8154 PIO/RAM 2                                               |
+-----------+-------------------------------+-------------------------------+
|1000-1FFF  | Peripherals                   | Peripherals                   |
| 1000-17FF |                               | 80x25 screen RAM (text)       |
| 1840-187F |                               | 80x25 6845 controller         |
| 1940-197F |                               | Econet                        |
|  1940     |                               |  6854 register 1              |
|  1941     |                               |  6854 register 2              |
|  1942     |                               |  6854 register 3              |
|  1943     |                               |  6854 Tx/Rx Data reg.         |
|  1944     |                               |  Station identification       |
+-----------+-------------------------------+-------------------------------+
|2000-7FFF  | Main system/user memory                                       |
| 2000-21FF |  DOS Catalogue buffer                                         |
| 2200-27FF |  DOS Sequential File buffers                                  |
| 2800-28FF |  Atom BASIC floating point variables                          |
| 2900-7FFF |  User memory                                                  |
+-----------+-------------------------------+-------------------------------+
|8000-9FFF  | Screen/user memory            | User memory                   |
| 8000-81FF |  Screen mode 0 (text)         |                               |
| 8000-83FF |  Screen mode 1 (1K graphics)  |                               |
| 8000-85FF |  Screen mode 2 (1.5K graphics)|                               |
| 8000-8BFF |  Screen mode 3 (3K graphics)  |                               |
| 8000-97FF |  Screen mode 4 (6K graphics)  |                               |
|           |                               |                               |
| xxxx-9FFF |  User memory                  |                               |
+-----------+-------------------------------+-------------------------------+
|A000-AFFF  | Econet/Extension ROM          | User memory                   |
+-----------+-------------------------------+-------------------------------+
|B000-BFFF  | I/O Devices                   | User memory                   |
| B000-B300 |  PPIA I/O (keyboard/CRTC/tape)|                               |
|  &B000    |  Keyboard                     |                               |
| B400-B7FF |  Econet controller            |                               |
|  B400     |   6854 register 1             |                               |
|  B401     |   6854 register 2             |                               |
|  B402     |   6854 register 3             |                               |
|  B403     |   6854 Tx/Rx Data reg.        |                               |
|  B404     |   Station identification      |                               |
| B800-BBFF |  6522 VIA for Printer         |                               |
| BCFF-BFFF |                               |                               |
+-----------+-------------------------------+-------------------------------+
|C000-CFFF  | Atom BASIC                                                    |
+-----------+-------------------------------+-------------------------------+
|D000-DFFF  | Floating Point                                                |
+-----------+-------------------------------+-------------------------------+
|E000-EFFF  | DOS/Econet ROM                                                |
+-----------+-------------------------------+-------------------------------+
|F000-FFFF  | VDU/COS/Monitor ROM                                           |
| F000-F7FF |  Graphics and assembler commands                              |
| F800-     |  COS/VDU/Monitor                                              |
| FFC0-FFFF |  MOS entry points                                             |
+-----------+-------------------------------+-------------------------------+