Registers
| Name | Alt Name | Usage |
| r0 | | Temporary accumulators |
| r1 | | Temporary accumulators |
| r2 | | |
| r3 | | |
| r4 | | |
| r5 | | Environment pointer |
| r6 | sp | Stack Pointer |
| r7 | pc | Program counter |
Memory Management
Page size: 128K (64 bytes)
Registers
| Name | Address | Usage |
| MMR0 | 0177572 | Memory Management Register #0 |
| MMR1 | 0177574 | Memory Management Register #1 (⚠️ PDP-11/44 and 11/70) |
| MMR2 | 0177576 | Fault virtual address |
| MMR3 | | Memory Management Register #3 (⚠️ PDP-11/44 and 11/70) |
MMR0
| Bits | Usage |
| 15 | Abort-Non Resident |
| 14 | Abort-Page / Length Error |
| 13 | Abort-Read Only / Access Violation |
| 12 | Trap-Memory Management (⚠️ PDP-11/70 only) |
| 11-10 | Reserved |
| 9 | Enable Memory Management Traps (⚠️ PDP-11/70 only) |
| 8 | Maintenance Mode (⚠️ Not used by PDP-11/24) |
| 7 | Instruction Completed (⚠️ PDP-11/70 only) |
| 6-5 | Page Mode |
| 4 | Page Address Space I/D (⚠️ PDP-11/44 and 11/70) |
| 3-1 | Page Number |
| 0 | Enable Relocation |
MMR1
| Bits | Usage |
| 15-11 | Amount changed |
| 10-8 | Register Number |
| 7-3 | Amount Changed |
| 2-0 | Register Number |
MMR3
| Bits | Usage |
| 15-6 | Reserved |
| 5 | Enable Unibus Map |
| 4 | Enable 22bit Mapping |
| 3 | Reserved |
| 2-0 | Mode |
| Value | Mode |
| 0b100 | Kernel |
| 0b010 | Supervisor |
| 0b001 | User |
1.9.1