| Abbreviation | Definition |
|---|---|
| RB | Rotate Buffer |
| RBA | Relative Byte Address |
| RBC | Reduced Block Command |
| RBR | Rotate Bits Randomly |
| RC | Release Command |
| RC | Return Code |
| RC | Right Check |
| RC | Run Command |
| RCL | Rotate Content Left |
| RCL | Rotate through Carry Left |
| RCR | Rotate through Carry Right |
| RCRB | Read Card Read Binary |
| RD | Register Destination |
| RD | Register Dump |
| RD | Rewind Disk |
| RDA | Refuse to Disclose Answer |
| RDW | Reference Divider Word |
| RE | Real and Equal |
| REC | Rounding Error Correction |
| REG | REGister |